F-1

(Address, Including Zip Code, and Telephone Number, Including Area Code, of Registrant’s Principal Executive Offices)

(Name, address, including zip code, and telephone number, including area code, of agent for service)

Approximate date of commencement of proposed sale to the public: As soon as practicable after the effective date of this registration statement.

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, check the following box. ¨

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ¨

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ¨

If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ¨

The Registrant hereby amends this registration statement on such date or dates as may be necessary to delay its effective date until the Registrant shall file a further amendment which specifically states that this registration statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933, as amended, or until the registration statement shall become effective on such date as the Commission, acting pursuant to such Section 8(a), may determine.

The information in this prospectus is not complete and may be changed. We may not sell these securities until the registration statement filed with the Securities and Exchange Commission is effective. This prospectus is not an offer to sell these securities, and we are not soliciting an offer to buy these securities in any state where the offer or sale is not permitted.

This is an initial public offering of ordinary shares by Prosensa Holding B.V. We are selling of our ordinary shares. The estimated initial public offering price is between $ and $ per share.

We intend to apply to have our ordinary shares listed on the Nasdaq Global Market under the symbol “RNA.”

We are an “emerging growth company” as that term is used in the Jumpstart Our Business Startups Act of 2012 and, as such, have elected to comply with certain reduced public company reporting requirements for future filings.

We have granted the underwriters an option for a period of 30 days to purchase up to an additional of our ordinary shares to cover over-allotments.

Investing in our ordinary shares involves a high degree of risk. See “Risk factors” beginning on page 9.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed on the adequacy or accuracy of this prospectus. Any representation to the contrary is a criminal offense.

Unless otherwise indicated or the context otherwise requires, all references in this prospectus to “Prosensa Holding B.V.,” “Prosensa Holding N.V.” or “Prosensa,” the “Company,” “we,” “our,” “ours,” “us” or similar terms refer to (i) Prosensa Holding B.V., together with its subsidiaries prior to the conversion of Prosensa Holding B.V. into Prosensa Holding N.V. and (ii) Prosensa Holding N.V., together with its subsidiaries, after giving effect to the conversion of Prosensa Holding B.V. into Prosensa Holding N.V., which is expected to occur immediately prior to the consummation of this offering. The trademarks, trade names and service marks appearing in this prospectus are the property of their respective owners.

We have not authorized anyone to provide any information other than that contained in this prospectus or in any free writing prospectus prepared by or on behalf of us or to which we may have referred you. We take no responsibility for, and can provide no assurance as to the reliability of, any other information that others may give you. We and the underwriters have not authorized any other person to provide you with different or additional information. Neither we nor the underwriters are making an offer to sell the ordinary shares in any jurisdiction where the offer or sale is not permitted. This offering is being made in the United States and elsewhere solely on the basis of the information contained in this prospectus. You should assume that the information appearing in this prospectus is accurate only as of the date on the front cover of this prospectus, regardless of the time of delivery of this prospectus or any sale of the ordinary shares. Our business, financial condition, results of operations and prospects may have changed since the date on the front cover of this prospectus.

Prospectus summary

This summary highlights information contained elsewhere in this prospectus. This summary may not contain all the information that may be important to you, and we urge you to read this entire prospectus carefully, including the “Risk factors,” “Business” and “Management’s discussion and analysis of financial condition and results of operations” sections and our consolidated audited and condensed consolidated unaudited financial statements, including the notes thereto, included in this prospectus, before deciding to invest in our ordinary shares.

Our company

We are an innovative biotechnology company engaged in the discovery and development of ribonucleic acid-modulating, or RNA-modulating, therapeutics for the treatment of genetic disorders. Our primary focus is on rare neuromuscular and neurodegenerative disorders with a large unmet medical need, including Duchenne muscular dystrophy, myotonic dystrophy and Huntington’s disease. Our clinical portfolio of RNA-based product candidates is focused on the treatment of Duchenne muscular dystrophy, or DMD. Each of our DMD compounds has been granted orphan drug status in the United States and the European Union.

DMD is one of the most prevalent rare genetic diseases globally affecting up to 1 in 3,500 boys and is invariably fatal. There is currently no approved disease-modifying therapy for DMD. The progressive muscle-wasting that characterizes this disease is caused by inadequate production of dystrophin, a protein necessary for muscle function, as a result of mutations in the dystrophin gene. The different mutations, which are mostly deletions of one or more exons, found in the dystrophin gene result in distinct sub-populations of DMD patients. We are designing product candidates to address several sub-populations using our platform technology. Our first product candidate, drisapersen, can address a variety of mutations in the dystrophin gene, such as a deletion of exon 50 or exons 48 to 50.

We started operations in 2002 and are located in Leiden, the Netherlands. We work closely with Leiden University Medical Center, or LUMC, with whom we entered into an exclusive licensing agreement in 2003 for LUMC’s proprietary RNA modulation exon-skipping technology to develop treatments for DMD, other neuromuscular disorders and indications outside the field of neuromuscular disorders. Since 2002, we have raised €56.4 million from private placements of equity securities, including to a number of venture capital firms. In addition, we have received grants and loans from several DMD-focused patient advocacy organizations to support our research of therapies for DMD. As of March 31, 2013, we had €36.1 million in cash and cash equivalents.

Clinical development of our lead product candidate, drisapersen, in DMD

Drisapersen is being developed in collaboration with GlaxoSmithKline, or GSK. Drisapersen aims to restore dystrophin expression and improve muscle condition and function in the largest known sub-population of DMD patients. In clinical trials, drisapersen has been shown to produce dystrophin expression and have a beneficial therapeutic effect on DMD patients. A Phase II placebo-controlled study of drisapersen in 53 DMD patients was completed and demonstrated a statistically significant and clinically important difference in the primary endpoint, which was the

distance walked in the six minute walk test, or 6MWD, between the placebo group and the continuous active-treatment group at a dose of 6 mg/kg/week after 24 weeks. This clinically meaningful benefit was maintained after 48 weeks of treatment, and drisapersen was well tolerated throughout the duration of this study.

Drisapersen successfully completed a twelve-patient Phase I/II study, and all patients were enrolled in an open-label extension study which has been ongoing since August 2009. The results indicate that drisapersen may lead to stabilization of the disease, as evidenced by an improvement or a slower than expected decline in the 6MWD, and the ongoing study continues to provide safety and tolerability data.

A pivotal Phase III study of drisapersen was initiated in December 2010, and results are expected in the fourth quarter of 2013. This study is a randomized, double-blind and placebo-controlled trial, assessing drisapersen at a dose of 6 mg/kg/week in 186 boys. The primary endpoint is the 6MWD at 48 weeks.

To date, over 300 patients have participated in clinical studies of drisapersen at more than 50 trial sites in 25 countries, and patient retention rates through March 2013 averaged 96% across all drisapersen clinical studies.

Our follow-on DMD compounds

PRO044, our next most advanced product candidate, addresses a separate sub-population of DMD patients. We developed PRO044 using our exon-skipping technology to generate a product candidate with the same mechanism of action that is used by drisapersen. PRO044 is currently in a Phase I/II study in Europe, which we expect to complete in mid-2013. We have four additional earlier-stage compounds that address other distinct sub-populations of DMD patients. Of these, PRO045 entered clinical trials in the first quarter of 2013, and we anticipate that PRO053 will enter clinical trials in mid-2013. PRO052 and PRO055 are in advanced preclinical development. We have also started a research program, PROSPECT, which includes a new and innovative application of our exon-skipping technology platform to specifically target rarer mutations in the dystrophin gene.

Our collaboration with GlaxoSmithKline

In 2009, we entered into an exclusive worldwide collaboration with GSK for the development and commercialization of RNA-based therapeutics for DMD, with GSK exclusively licensing worldwide rights to develop and commercialize drisapersen and obtaining an option to exclusively license PRO044.

above, we will retain the option to certain commercial rights in a selected European territory. All of our other DMD compounds fall outside of the scope of this agreement, and we intend to develop and commercialize them ourselves or consider partnerships.

Upon entering into the agreement with GSK, we received a £16 million (€17.2 million) nonrefundable upfront payment from GSK and have received £41.5 million (€47.4 million) in total under the agreement. Including amounts already paid, we are eligible for up to £428 million (€505 million) in total milestone payments under the agreement. We are also entitled to receive percentage royalties in the low tens on future global sales of drisapersen and each of the other compounds that GSK licenses and successfully commercializes.

Our RNA modulation technology platform

Our DMD programs are part of our broader RNA modulation platform technology, which in addition to exon skipping, is focused on reducing mutant RNA associated with trinucleotide repeat expansion diseases. Our current programs in this area are PRO135 for myotonic dystrophy (DM1) and PRO289 for Huntington’s disease (HD). Both DM1 and HD are rare diseases with a severe impact on patients, and currently no disease-modifying therapies exist for either.

Our business strategy

Our goal is to become a leader in the rare genetic disease field, with a particular focus on DMD. Over time, we intend to mature into a fully integrated biopharmaceutical company focused on the discovery, development and commercialization of our products.

The key components of our business objectives are:

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Collaborate with our partner, GSK, to rapidly advance drisapersen, our lead DMD candidate;

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Leverage our know-how from drisapersen to accelerate and reduce development risk of our earlier-stage DMD products;

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Independently commercialize our proprietary products in DMD;

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Leverage our proprietary RNA modulation and exon-skipping drug discovery platform; and

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Continue to invest in and strengthen our intellectual property portfolio.

We may also enter into strategic collaborations that deliver additional expertise and enhance implementation of our strategy.

Corporate information

We are a Dutch private company with limited liability, and prior to the consummation of this offering we intend to convert to a Dutch public company with limited liability. Our principal executive offices are located at J.H. Oortweg 21, 2333 CH Leiden, the Netherlands. Our telephone number at this address is +31 (0)71 33 22 100.

Investors should contact us for any inquiries at the address and telephone number of our principal executive office. Our principal website is www.prosensa.com. The information contained on our website is not a part of this prospectus.

Risks associated with our business

Our business is subject to a number of risks of which you should be aware before making an investment decision. These risks are discussed more fully in the “Risk factors” section of this prospectus immediately following this prospectus summary. These risks include the following:

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We currently have no commercial products, and we have not received regulatory approval for, nor have we generated commercial revenue from, any of our product candidates.

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We depend heavily on the success of drisapersen. Our ability to generate royalty and product revenues will depend heavily on the successful development of drisapersen and our other product candidates, which may not occur for several years, if ever.

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Our financial prospects for the next several years are substantially dependent on the development and marketing efforts of our partner GSK for drisapersen and the other product candidates that it may license under our collaboration.

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Drisapersen and our other product candidates are in clinical and preclinical development, and clinical trials of these product candidates may not be successful. If GSK or we are unable to obtain marketing approvals for, or successfully commercialize, drisapersen or our other product candidates, our ability to generate revenue may be materially impaired.

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We have a history of operating losses and anticipate that we will continue to incur losses for the foreseeable future. As of March 31, 2013, we had an accumulated deficit of €44.2 million. We may need additional funding, and such funding may cause substantial dilution to our shareholders.

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We may be unable to maintain and protect our intellectual property assets, which could harm our ability to compete and impair our business.

Implications of being an emerging growth company

We qualify as an “emerging growth company” as defined in the Jumpstart our Business Startups Act of 2012, or the JOBS Act. An emerging growth company may take advantage of specified reduced reporting and other burdens that are otherwise applicable generally to public companies. These provisions include:

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the ability to include only two years of audited financial statements and only two years of related management’s discussion and analysis of financial condition and results of operations disclosure; and

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an exemption from the auditor attestation requirement in the assessment of our internal control over financial reporting pursuant to the Sarbanes-Oxley Act of 2002.

We may take advantage of these provisions for up to five years or such earlier time that we are no longer an emerging growth company. We would cease to be an emerging growth company if we have more than $1.0 billion in annual revenue, have more than $700 million in market value of our ordinary shares held by non-affiliates or issue more than $1.0 billion of non-convertible debt over a three-year period.

The offering



Ordinary shares offered by us		ordinary shares.

Ordinary shares to be outstanding after this offering		ordinary shares.

Over-allotment option		We have granted the underwriters the right to purchase up to an additional ordinary shares from us within 30 days of the date of this prospectus, to cover over-allotments, if any, in connection with the offering.

Use of proceeds		We estimate that the net proceeds to us from the offering will be approximately $ (€ ). We currently expect that we will use the net proceeds from this offering, together with our cash and cash equivalents on hand, as follows: • approximately € million to fund our current DMD development portfolio for which we bear expenses (PRO045, PRO053, PRO052 and PRO055), PROSPECT and DMD-support projects, including our DMD natural history study; • approximately € million to fund non-DMD projects, including DM1 and HD; and • the remainder for working capital and other general corporate purposes. See “Use of proceeds.”

Dividend policy		We have never paid or declared any cash dividends on our ordinary shares, and we do not anticipate paying any cash dividends on our ordinary shares in the foreseeable future.

Risk factors		See “Risk factors” and the other information included in this prospectus for a discussion of factors you should consider before deciding to invest in our ordinary shares.

Listing		We intend to apply to list our ordinary shares on the Nasdaq Global Market, or Nasdaq, under the symbol “RNA.”

The number of our ordinary shares to be outstanding after this offering is based on 3,491,058 of our ordinary shares outstanding as of March 31, 2013 and 25,511,240 additional ordinary shares issuable upon the automatic conversion of all of our outstanding preferred shares into ordinary shares

immediately prior to the consummation of this offering (the Share Conversion) pursuant to our shareholders’ agreement, as described under “Related party transactions—Shareholders’ agreement.”

The number of our ordinary shares to be outstanding after this offering excludes:

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2,207,707 of our ordinary shares issuable upon the exercise of options outstanding as of March 31, 2013 at a weighted average exercise price of €0.34 per share; and

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352,370 additional options for depositary receipts in respect of our ordinary shares, restricted shares and restricted share units for depositary receipts in respect of our ordinary shares available for future issuance as of March 31, 2013 under our 2010 equity incentive plan.

Unless otherwise indicated, all information contained in this prospectus:

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gives effect to the conversion of all of our outstanding preferred shares into an aggregate of 25,511,240 ordinary shares immediately prior to the consummation of this offering, which we refer to as the Share Conversion;

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gives effect to the amendment of our articles of association as adopted by our general meeting of shareholders in connection with the consummation of this offering; and

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assumes no exercise of the option granted to the underwriters to purchase up to additional ordinary shares to cover over-allotments, if any, in connection with the offering.

Summary financial information

The summary income statement and balance sheet data for the years ended and as of December 31, 2012 and 2011 of Prosensa Holding B.V. are derived from the consolidated financial statements included in this prospectus. The summary income statement and balance sheet data for the three months ended and as of March 31, 2013 and 2012 are derived from the unaudited condensed consolidated financial statements included in this prospectus. We maintain our books and records in euros (€), and we prepare our financial statements under International Financial Reporting Standards, or IFRS, as issued by the International Accounting Standards Board, or the IASB.

This financial information should be read in conjunction with “Presentation of financial and other information,” “Management’s discussion and analysis of financial condition and results of operations” and our consolidated audited and unaudited financial statements, including the notes thereto, included in this prospectus.

Consolidated statement of comprehensive income data


	Year ended December 31,						Three months ended March 31,
(€ in thousands)	2011			2012			2012			2013

License revenue	€	6,510		€	5,726		€	1,385		€	1,407
Collaboration revenue		2,179			2,127			589			993

Total revenue		8,689			7,853			1,974			2,400

Other income		36			174			0			1
Research and development expense		(15,348	)		(14,393	)		(3,781	)		(4,060	)
General and administrative expense		(5,203	)		(4,023	)		(1,061	)		(1,795	)
Other gains/(losses)—net		22			49			3			1

Operating loss		(11,804	)		(10,340	)		(2,865	)		(3,453	)

Finance income		434			796			212			192
Finance costs		(209	)		(348	)		(82	)		(188	)

Finance income—net		225			448			130			4

Other comprehensive income		0			0			0			0

Total comprehensive loss	€	(11,579	)	€	(9,892	)	€	(2,735	)	€	(3,449	)


Net loss per share
Basic and diluted(1)		(0.60	)		(0.37	)		(0.12	)		(0.12	)

Weighted-average shares outstanding(2)
Basic		19,240,137			26,574,570			23,145,096			29,002,298
Diluted		20,656,759			28,110,543			24,562,830			31,210,005
Pro forma net loss per share (unaudited)(3)				€	(0.37	)	€	(0.12	)	€	(0.12	)

(1)

Basic and diluted net loss per share are the same in these periods because outstanding options and restricted shares would be anti-dilutive due to our net loss in these periods.

(2)

Includes preferred shares.

(3)

The unaudited pro forma net loss per share data give effect to the automatic conversion of all of our preferred shares into an aggregate of 25,511,240 shares of our ordinary shares immediately prior to the consummation of this offering (the Share Conversion as described under “Related party transactions—Shareholders’ agreement”). The pro forma information is presented for informational purposes only and is not necessarily indicative of what our results would have been had the Share Conversion actually occurred on such date nor is it indicative of our future performance.

Consolidated balance sheet data


	As of December 31, 2012			As of March 31, 2013
(€ in thousands)	Actual			Actual			Pro forma(1)


Cash and cash equivalents		40,738			36,115
Working capital (deficit)(2)		(2,353	)		(2,349	)
Total assets		47,329			43,360
Long-term debt, including current portion		6,541			6,682
Accumulated (deficit)		(40,834	)		(44,225	)
Total shareholders’ equity		15,574			12,183

(1)

The unaudited pro forma balance sheet data give effect to the Share Conversion upon the consummation of this offering and to the issuance and sale of ordinary shares in this offering by us at an assumed initial public offering price of $ per share, the midpoint of the range set forth on the cover page of this prospectus, and the application of the net proceeds of the offering, after deducting estimated underwriting discounts and commissions and offering expenses payable by us, as set forth under “Use of proceeds.” Because the conversion of our preferred shares into ordinary shares will occur on a one-to-one basis, the Share Conversion will have no impact on total shareholders’ equity. See “Use of proceeds” and “Capitalization.” The pro forma information is presented for informational purposes only and is not necessarily indicative of what our results would have been had these transactions actually occurred on such date nor is it indicative of our future performance.

(2)

Working capital (deficit) is calculated as current assets excluding cash and cash equivalents less trade and other payables.

You should carefully consider the risks and uncertainties described below and the other information in this prospectus before making an investment in our ordinary shares. Our business, financial condition or results of operations could be materially and adversely affected if any of these risks occurs, and as a result, the market price of our ordinary shares could decline and you could lose all or part of your investment. This prospectus also contains forward-looking statements that involve risks and uncertainties. See “Cautionary statement regarding forward-looking statements.” Our actual results could differ materially and adversely from those anticipated in these forward-looking statements as a result of certain factors.

We depend heavily on the success of drisapersen. Drisapersen and all of our other product candidates are still in preclinical and clinical development. Clinical trials of our product candidates may not be successful. If we and GlaxoSmithKline are unable to commercialize drisapersen and our other product candidates, or experience significant delays in doing so, our business, financial condition and results of operations will be materially adversely affected.

We have invested a significant portion of our efforts and financial resources in the development of drisapersen and our other five product candidates, all targeting patients with Duchenne muscular dystrophy, or DMD. All of our product candidates are still in preclinical and clinical development. Our ability to generate royalty and product revenues, which we do not expect will occur for at least the next several years, if ever, will depend heavily on the successful development and eventual commercialization of these product candidates, particularly drisapersen. The success of drisapersen and our product candidates will depend on several factors, including the following:

If we or GSK, as applicable, do not achieve one or more of these factors in a timely manner or at all, we could experience significant delays or an inability to successfully commercialize drisapersen and our other product candidates, which would materially adversely affect our business, financial condition and results of operations.

Because we are developing product candidates for the treatment of diseases in which there is little clinical experience and, in some cases, using new endpoints or methodologies, there is more risk that the outcome of our clinical trials will not be favorable.

There is currently no approved disease-modifying therapy for DMD. In addition, there has been limited historical clinical trial experience generally for the development of drugs to treat the underlying cause of DMD. As a result, the design and conduct of clinical trials for this disease, particularly for drugs to address the underlying cause of this disease, is subject to increased risk. In particular, regulatory authorities in the United States and European Union have not issued definitive guidance as to how to measure and achieve efficacy.

In the last several years, the six minute walk test, or 6MWT, has been used in several trials of product candidates for patients with DMD, and is accepted by U.S. and European regulators to be an appropriate primary outcome measure for DMD trials. We may nonetheless experience setbacks with the Phase III clinical trial or any other clinical trial for drisapersen or the clinical trials for our other product candidates because of the limited clinical experience in this indication. For example, regulators have not yet established what difference in the distance walked in the 6MWT, or 6MWD, is required to be demonstrated in a clinical trial of a DMD therapy in order to signify a clinically meaningful result and/or obtain regulatory approvals. As a result, we may not achieve the pre-specified endpoint with statistical significance in the trials of drisapersen or of our other product candidates, which would decrease the chance of obtaining marketing approval for drisapersen or our other product candidates for DMD. We could also face similar challenges in designing clinical trials and obtaining regulatory approval for future product candidates, including any that we may develop for myotonic dystrophy (DM1) or Huntington’s disease (HD) because there is also limited historical clinical trial experience for the development of drugs to treat these diseases.

Our financial prospects for the next several years are substantially dependent upon the development and marketing efforts of GSK for our lead candidate drisapersen and the other DMD product candidates that it may license under our collaboration, and our continuing strategic relationship with GSK. GSK may act in its best interest rather than in our best interest, which could materially adversely affect our business, financial condition and results of operations.

We rely on GSK to fund and conduct the clinical development and commercialization of drisapersen and the other product candidates GSK may license under our collaboration, and GSK has complete control over such activities. Our ability to generate revenue in the near term will depend primarily on the successful development, regulatory approval, marketing and commercialization of drisapersen by GSK. Such success is subject to significant uncertainty, and we have limited control over the resources, time and effort that GSK may devote to drisapersen. Any of several events or factors could have a material adverse effect on our ability to generate revenue from GSK’s potential commercialization of drisapersen. For example, GSK:

Pursuant to our collaboration with GSK, GSK will fund all our costs and expenses associated with the further clinical development of, and has sole decision-making authority and is responsible for all research, development, regulatory, manufacturing, marketing, advertising, promotional, launch and sales and other commercial activities in connection with drisapersen and each other compound that it receives a license for under the collaboration. In return, we are to receive milestone payments upon successful compound development and percentage royalties in the low tens on product sales. The milestones generally relate to development and regulatory achievements, and a portion of the milestone payments relate to drisapersen. If we fail to maintain this relationship with GSK, or GSK fails to honor its agreements under the collaboration, our business and results of operations could be materially and adversely affected.

In addition, GSK has the right to make decisions regarding the development and commercialization of product candidates under the collaboration without consulting us and may make decisions with which we do not agree. Conflicts between GSK and us may arise if there is a dispute about the progress of the clinical development of a product candidate, the achievement and payment of a milestone amount or the ownership of intellectual property developed during the course of our collaboration agreement. It may be necessary for us to assume responsibility at our own expense for the development of drisapersen or our other product candidates subject to the GSK collaboration. In that event, we would likely be required to limit the size and scope of one or more of our programs or increase our expenditures and seek additional funding, which may not be available on acceptable terms or at all, which would materially adversely affect our business, financial condition and results of operations.

We do not and will not have access to all information regarding the product candidates we license to GSK. Consequently, our ability to inform our shareholders about the status of such product candidates, and to make informed operational and investment decisions about the product candidates to which we have retained development and commercialization rights, may be limited.

We do not and will not have access to all information regarding the products being developed and potentially commercialized by GSK, including potentially material information about clinical trial design and execution, safety reports from clinical trials, spontaneous safety reports if the product is later approved and marketed, regulatory affairs, process development, manufacturing, marketing and other areas known by GSK. In addition, we have confidentiality obligations under our agreement with GSK. Thus, our ability to keep our shareholders informed about the status of product candidates under our collaboration will be limited by the degree to which GSK keeps us informed and allows us to disclose such information to the public. If GSK fails to keep us informed about the clinical development and regulatory approval of our collaboration and product candidates licensed to it, we may make operational and investment decisions that we would not have made had we been fully informed, which may materially and adversely affect our business and operations.

We have a history of operating losses, and we may not achieve or sustain profitability. We anticipate that we will continue to incur losses for the foreseeable future. If we fail to obtain additional funding to conduct our planned research and development effort, we could be forced to delay, reduce or eliminate our product development programs or commercial development efforts.

We incurred net losses of €9.9 million and €11.6 million for the years ended December 31, 2012 and 2011, respectively, and net losses of €3.4 million and €2.7 million for the three months ended March 31, 2013 and 2012, respectively. As of March 31, 2013, we had an accumulated deficit of €44.2 million. Our losses have resulted principally from expenses incurred in research and development of our product candidates and from general and administrative expenses that we have incurred while building our business infrastructure. We expect to continue to incur significant operating losses in the future as we continue our research and development efforts and seek to obtain regulatory approval and commercialization of our product candidates. In our fiscal year ending December 31, 2013, we expect to incur in the range of €20-25 million of costs associated with research and development, which amount is exclusive of costs incurred by GSK in developing our licensed product candidate drisapersen and other amounts received from GSK under the collaboration in connection with the development of our other DMD product candidates.

To date, we have financed our operations through private placements of equity securities, upfront, milestone and expense reimbursement payments received from GSK under our collaboration and funding from patient organizations, governmental bodies and bank loans. To date we have not generated any revenues from product sales. Based on our current plans, we do not expect to generate significant royalty or product revenues unless and until GSK or we obtain marketing approval for, and commercialize, drisapersen or any of our product candidates for which we have retained commercialization rights. We believe that the net proceeds of this offering, together with our existing cash and cash equivalents and anticipated milestone payments under the GSK Agreement, will enable us to fund our operating expenses and capital expenditure requirements for at least the next months. We have based this estimate on

assumptions that may prove to be wrong, and we could use our capital resources sooner than we currently expect.

We may have to seek additional funding. Additional funds may not be available on a timely basis, on favorable terms, or at all, and such funds, if raised, may not be sufficient to enable us to continue to implement our long-term business strategy. In addition, we may not be able to obtain further funding from patient organizations or governmental bodies.

Even if we do generate product royalties or product sales, we may never achieve or sustain profitability on a quarterly or annual basis. Our failure to sustain profitability would depress the market price of our ordinary shares and could impair our ability to raise capital, expand our business, diversify our product offerings or continue our operations. A decline in the market price of our ordinary shares also could cause you to lose all or a part of your investment.

Raising additional capital may cause dilution to our shareholders, including purchasers of ordinary shares in this offering, restrict our operations or require us to relinquish rights to our technologies or product candidates.

Until such time, if ever, as we can generate substantial product revenues, we expect to finance our cash needs through a combination of the net proceeds of this offering, together with our existing cash and cash equivalents and anticipated milestone payments under our collaboration with GSK. In the event we need to seek additional funds, however, we may raise additional capital through the sale of equity or convertible debt securities. In such an event, your ownership interest will be diluted, and the terms of these securities may include liquidation or other preferences that adversely affect your rights as a holder of our ordinary shares. Debt financing, if available, may involve agreements that include covenants limiting or restricting our ability to take specific actions, such as incurring additional debt, making capital expenditures or declaring dividends.

If we raise additional funds through collaborations, strategic alliances or marketing, distribution or licensing arrangements with third parties, we may have to relinquish valuable rights to our technologies, future revenue streams or product candidates or to grant licenses on terms that may not be favorable to us. If we are unable to raise additional funds when needed, we may be required to delay, limit, reduce or terminate our product development or future commercialization efforts or grant rights to develop and market product candidates that we would otherwise prefer to develop and market ourselves.

Exchange rate fluctuations or abandonment of the euro currency may materially affect our results of operations and financial condition.

Due to the international scope of our operations, fluctuations in exchange rates, particularly between the euro, the British pound and the U.S. dollar, may adversely affect us. Although we are based in the Netherlands, we source research and development, manufacturing, consulting and other services from several countries. In addition, our arrangements with GSK are denominated in British pounds. Further, potential future revenue may be derived from abroad, particularly from the United States. As a result, our business and share price may be affected by fluctuations in foreign exchange rates between the euro and these other currencies, which may also have a significant impact on our reported results of operations and cash flows from period to period. Currently, we do not have any exchange rate hedging arrangements in place.

In addition, the possible abandonment of the euro by one or more members of the European Union could materially affect our business in the future. Despite measures taken by the European Union to provide funding to certain E.U. member states in financial difficulties and by a number of European countries to stabilize their economies and reduce their debt burdens, it is possible that the euro could be abandoned in the future as a currency by countries that have adopted its use. This could lead to the re-introduction of individual currencies in one or more E.U. member states, or in more extreme circumstances, the dissolution of the European Union. The effects on our business of a potential dissolution of the European Union, the exit of one or more E.U. member states from the European Union or the abandonment of the euro as a currency, are impossible to predict with certainty, and any such events could have a material adverse effect on our business, financial condition and results of operations.

Risks related to the development and clinical testing of our product candidates

Clinical drug development involves a lengthy and expensive process with uncertain timelines and uncertain outcomes. If clinical trials of our product candidates are prolonged or delayed, we or our collaborator may be unable to obtain required regulatory approvals, and therefore be unable to commercialize our product candidates on a timely basis or at all.

To obtain the requisite regulatory approvals to market and sell any of our product candidates, we or our collaborator for such candidate must demonstrate through extensive preclinical and clinical trials that our products are safe and effective in humans. The process for obtaining governmental approval to market our products is rigorous, time-consuming and costly. It is impossible to predict the extent to which this process may be affected by legislative and regulatory developments. Due to these and other factors, such as the fact that no product using antisense oligonucleotides, or AONs, for systemic use has been approved for sale in the European Union and only one AON is approved for systemic use in the United States, our current product candidates or any of our other future product candidates could take a significantly longer time to gain regulatory approval than expected or may never gain regulatory approval. This could delay or eliminate any potential product revenue by delaying or terminating the potential commercialization of our product candidates.

Clinical trials must be conducted in accordance with EMA, FDA and other applicable regulatory authorities’ legal requirements, regulations or guidelines, and are subject to oversight by these governmental agencies and Institutional Review Boards, or IRBs, at the medical institutions where the clinical trials are conducted. In addition, clinical trials must be conducted with supplies of our product candidates produced under current good manufacturing practices, or cGMP, and other requirements. We depend on GSK (for drisapersen and other licensed product candidates) and on medical institutions and clinical research organizations, or CROs (for our other compounds), to conduct our clinical trials in compliance with Good Clinical Practice, or GCP. To the extent GSK and or the CROs fail to enroll participants for our clinical trials, fail to conduct the study to GCP standards or are delayed for a significant time in the execution of trials, including achieving full enrollment, we may be affected by increased costs, program delays or both, which may harm our business. In addition, clinical trials are conducted in countries outside the European Union and the United States, which may subject us to further delays and expenses as a result of increased shipment costs, additional regulatory requirements and the engagement of non-E.U. and non-U.S. CROs, as well as expose us to risks associated with clinical investigators who are unknown to the EMA or the FDA, and different standards of diagnosis, screening and medical care.

To date, we have not completed all clinical trials required for the approval of any of our product candidates. Our lead compound drisapersen is in Phase III trials. The trials of our other compounds are less advanced or have not yet started. The commencement and completion of clinical trials for our products may be delayed, suspended or terminated as a result of many factors, including but not limited to:

Since we have adopted a platform technology approach and all of our current clinical development candidates use similar process technology and are similarly applied to DMD, any of the above unforeseen difficulties that arises with one of our clinical development candidates may negatively affect all of our product candidates.

Positive or timely results from preclinical trials do not ensure positive or timely results in late stage clinical trials or product approval by the EMA, the FDA or other regulatory authorities.

Products that show positive preclinical or early clinical results may not show sufficient safety or efficacy to obtain regulatory approvals and therefore fail in later stage clinical trials. The EMA, the FDA and other regulatory authorities have substantial discretion in the approval process, and determining when or whether regulatory approval will be obtained for any of our product candidates. Even if we believe the data collected from clinical trials of our product candidates are promising, such data may not be sufficient to support approval by the EMA, the FDA or any other regulatory authority.

Any delay in commencing or completing clinical trials for our products could increase our product development costs and delay marketing approval and commercialization of our products. For instance, in 2009 we held a pre-IND meeting with the FDA to discuss PRO044 clinical studies, and the FDA determined that we had insufficient data at that time to support the initiation of a clinical trial of PRO044 in the United States. PRO044 continues to be on clinical hold in the United States pending the results of long-term preclinical safety studies that we anticipate will be completed in the fourth quarter of 2013. In addition, in 2010, the FDA determined that inadequate data had been presented to support long-term studies of drisapersen and requested additional safety data. Upon submission of additional data, the FDA lifted the clinical hold on drisapersen in 2011.

In addition, it is possible that the FDA may not consider the results of GSK’s Phase III clinical trial of drisapersen, once completed, to be sufficient for the approval of drisapersen for DMD patients. In general, the FDA has usually suggested two adequately designed and powered and well-controlled trials to demonstrate effectiveness. Even if favorable results are achieved in the Phase III trial of drisapersen, the FDA may nonetheless require that GSK conduct additional clinical trials, possibly using a different design.

It is also possible that none of our products will complete clinical trials in any of the markets in which we intend to sell those products. If this were to happen, we would not receive the regulatory approvals needed and neither we nor our collaborator would be able to market our products. Significant clinical trial delays could also allow our competitors to bring products to market before we do or shorten any periods during which we have the exclusive right to commercialize our product candidates and impair our ability to commercialize our product candidates and may harm our business and results of operations.

Failure to obtain marketing authorization for our product candidates will result in our being unable to market and sell such products, which would materially adversely affect our business, financial conditional and results of operation. Approval by one regulatory authority does not ensure approval by regulatory authorities in other jurisdictions. If we fail to obtain approval in any jurisdiction, the geographic market for our product candidates could be limited. Similarly, regulatory agencies may not approve the labeling claims that are necessary or desirable for the successful commercialization of our product candidates.

If serious adverse, undesirable or unacceptable side effects are identified during the development of our product candidates, we may need to abandon our development of such product candidates.

If our product candidates are associated with serious adverse, undesirable or unacceptable side effects, we may need to abandon their development or limit development to certain uses or sub-populations in which such side effects are less prevalent, less severe or more acceptable from a risk-benefit perspective. Many compounds that initially showed promise in early-stage or clinical

testing have later been found to cause side effects that prevented further development of the compound.

Transient proteinuria (protein in the urine) was observed in all twelve patients in our Phase I/II study of drisapersen, and eleven patients demonstrated signs of proteinuria at week twelve of the extension phase of this trial. Other reported adverse events from this study included injection site reactions, which were seen to varying degrees of severity in all subjects, raised cystatin C (a protein indicative of kidney function), decreased C3 (a protein indicating immunological activity), low platelet counts and raised liver enzymes, including GLDH and gamma GT, which may indicate abnormal liver function. In addition, clinical trial experience to date with drisapersen in trials that GSK is conducting indicates adverse events that include proteinuria, local injection site reactions (pain, bruising, erythema, induration, pigmentation), thrombocytopenia (decrease in the amount of platelets in the blood) and increases in certain liver enzymes. In addition to the adverse events noted above, single reports have been received of the following clinical conditions: intracranial venous sinus thrombosis (blood clot), extramembranous glomerulonephritis (inflammation affecting part of the kidney) and nephrotic-linked proteinuria. Such side effects could be raised by the FDA, the EMA and other regulatory authorities and could be an impediment to receipt of marketing approval or physician or patient acceptance of drisapersen or our other product candidates because of concerns related to safety.

We depend on enrollment of patients in our clinical trials for our product candidates. If we are unable to enroll patients in our clinical trials, our research and development efforts and business, financial condition and results of operations could be materially adversely affected.

Successful and timely completion of clinical trials will require that we enroll a sufficient number of patient candidates. Trials may be subject to delays as a result of patient enrollment taking longer than anticipated or patient withdrawal. Patient enrollment depends on many factors, including the size of the patient population, eligibility criteria for the trial, the proximity of patients to clinical sites, the nature of the trial protocol, competing clinical trials and the availability of new drugs approved for the indication the clinical trial is investigating.

The successful completion of our clinical trials for our DMD product candidates is dependent upon our ability to enroll a sufficient number of patients in the sub-populations of DMD patients that our particular product candidates target. Our product candidates focus on the treatment of DMD, which is a rare disease with a small patient population. As our products target sub-populations of DMD patients and trial enrollment is limited to boys in a certain age range only, the number of patients eligible for our trials is even smaller. Further, there are only a limited number of specialist physicians and major clinical centers are concentrated in a few geographic regions. In addition, other companies are conducting clinical trials and have announced plans for future clinical trials that are seeking, or are likely to seek, to enroll patients with the same conditions that we are studying and patients are generally only able to enroll in one single trial at a time. The small population of patients, competition for these patients and the limited trial sites may make it difficult for us to enroll enough patients to complete our clinical trials in a timely and cost-effective manner.

We may become exposed to costly and damaging liability claims, either when testing our product candidates in the clinic or at the commercial stage; and our product liability insurance may not cover all damages from such claims.

We are exposed to potential product liability and professional indemnity risks that are inherent in the research, development, manufacturing, marketing and use of pharmaceutical products. Currently we have no products that have been approved for commercial sale; however, the current and future use of product candidates by us and our corporate collaborators in clinical trials, and the sale of any approved products in the future, may expose us to liability claims. These claims might be made by patients that use the product, healthcare providers, pharmaceutical companies, our corporate collaborators or others selling such products. Any claims against us, regardless of their merit, could be difficult and costly to defend and could materially adversely affect the market for our product candidates or any prospects for commercialization of our product candidates.

Although the clinical trial process is designed to identify and assess potential side effects, it is always possible that a drug, even after regulatory approval, may exhibit unforeseen side effects. If any of our product candidates were to cause adverse side effects during clinical trials or after approval of the product candidate, we may be exposed to substantial liabilities. Physicians and patients may not comply with any warnings that identify known potential adverse effects and patients who should not use our product candidates.

Although we maintain limited product liability insurance for our product candidates, it is possible that our liabilities could exceed our insurance coverage. We intend to expand our insurance coverage to include the sale of commercial products if we obtain marketing approval for any of our product candidates. However, we may not be able to maintain insurance coverage at a reasonable cost or obtain insurance coverage that will be adequate to satisfy any liability that may arise. If a successful product liability claim or series of claims is brought against us for uninsured liabilities or in excess of insured liabilities, our assets may not be sufficient to cover such claims and our business operations could be impaired.

Should any of the events described above occur, this could have a material adverse effect on our business, financial condition and results of operations.

Even if our product candidates obtain regulatory approval, they will be subject to continual regulatory review.

If marketing authorization is obtained for any of our product candidates, the product will remain subject to continual review and therefore authorization could be subsequently withdrawn or restricted. We will be subject to ongoing obligations and oversight by regulatory authorities, including adverse event reporting requirements, marketing restrictions and, potentially, other post-marketing obligations, all of which may result in significant expense and limit our ability to commercialize such products.

If there are changes in the application of legislation or regulatory policies, or if problems are discovered with a product or our manufacture of a product, or if we or one of our distributors, licensees or co-marketers fails to comply with regulatory requirements, the regulators could take various actions. These include imposing fines on us, imposing restrictions on the product or its manufacture and requiring us to recall or remove the product from the market. The regulators could also suspend or withdraw our marketing authorizations, requiring us to conduct additional

clinical trials, change our product labeling or submit additional applications for marketing authorization. If any of these events occurs, our ability to sell such product may be impaired, and we may incur substantial additional expense to comply with regulatory requirements, which could materially adversely affect our business, financial condition and results of operations.

Due to our limited resources and access to capital, we must and have in the past decided to prioritize development of certain product candidates; these decisions may prove to have been wrong and may adversely affect our revenues.

Because we have limited resources and access to capital to fund our operations, we must decide which product candidates to pursue and the amount of resources to allocate to each. Our decisions concerning the allocation of research, collaboration, management and financial resources toward particular compounds, product candidates or therapeutic areas may not lead to the development of viable commercial products and may divert resources away from better opportunities. Similarly, our decisions to delay, terminate or collaborate with third parties in respect of certain product development programs may also prove not to be optimal and could cause us to miss valuable opportunities. If we make incorrect determinations regarding the market potential of our product candidates or misread trends in the biopharmaceutical industry, in particular for DMD therapies, our business, financial condition and results of operations could be materially adversely affected.

Because we are subject to environmental, health and safety laws and regulations, we may become exposed to liability and substantial expenses in connection with environmental compliance or remediation activities which may adversely affect our business and financial condition.

Our operations, including our research, development, testing and manufacturing activities, are subject to numerous environmental, health and safety laws and regulations. These laws and regulations govern, among other things, the controlled use, handling, release and disposal of, and the maintenance of a registry for, hazardous materials and biological materials, such as chemical solvents, human cells, carcinogenic compounds, mutagenic compounds and compounds that have a toxic effect on reproduction, laboratory procedures and exposure to blood-borne pathogens. If we fail to comply with such laws and regulations, we could be subject to fines or other sanctions.

As with other companies engaged in activities similar to ours, we face a risk of environmental liability inherent in our current and historical activities, including liability relating to releases of or exposure to hazardous or biological materials. Environmental, health and safety laws and regulations are becoming more stringent. We may be required to incur substantial expenses in connection with future environmental compliance or remediation activities, in which case, our production and development efforts may be interrupted or delayed and our financial condition and results of operations may be materially adversely affected.

Our research and development activities could be affected or delayed as a result of possible restrictions on animal testing.

Certain laws and regulations require us to test our product candidates on animals before initiating clinical trials involving humans. Animal testing activities have been the subject of controversy and adverse publicity. Animal rights groups and other organizations and individuals

have attempted to stop animal testing activities by pressing for legislation and regulation in these areas and by disrupting these activities through protests and other means. To the extent the activities of these groups are successful, our research and development activities may be interrupted, delayed or become more expensive.

Our ability to obtain marketing approval for the product candidates to which we have retained commercialization rights depends on GSK obtaining marketing approval for drisapersen and the success of our regulatory strategy for our candidates that target ultra-orphan sub-populations of DMD patients. If either is not successful, we may not obtain marketing approvals for our product candidates.

GSK controls the regulatory approval application process for drisapersen, including how it communicates with regulators and makes the case for marketing approval. If GSK is not successful in obtaining marketing approval for drisapersen, or does so in a way that is limiting with respect to our other DMD product candidates, our ability to obtain regulatory approval for such product candidates, and consequently our business and results of operations, could be adversely affected.

Our regulatory strategy for obtaining approval for the product candidates to which we have retained commercialization rights depends on the acceptance of our proposed extrapolation principle that if exon skipping works for one AON compound that is shown to be safe and effective, then the principle should to a certain extent also apply to subsequent compounds for rarer sub-populations. Because DMD is a rare disease and our product candidates after drisapersen target smaller sub-populations for which it is less feasible to conduct placebo-controlled studies, our ability to obtain marketing approval may be dependent on regulators’ acceptance of this extrapolation principle. If regulators do not accept this principle, we may be delayed in or prevented from obtaining marketing approval.

No exon-skipping therapies using AONs for systemic use have yet been approved or marketed in the European Union, and only one AON for systemic use has been approved in the United States.

Our exon-skipping therapy using AONs is intended to correct genetic defects that cause disease in humans, and our current product candidates target DMD. Our compounds have not yet been incorporated into a commercial product and are still in development. To date, no product using AONs for systemic use has been approved for sale in the European Union. In the United States currently only one AON is approved by the FDA for systemic use. Therefore, we are not certain that our technology will meet the applicable safety and efficacy standards of the regulatory authorities. In addition, any regulatory setbacks faced by third parties developing similar compounds could affect the receptiveness of regulators to our compounds.

Any failures or setbacks involving our therapy, including adverse effects resulting from the use of this therapy in humans, could have a detrimental impact on our internal product candidate pipeline and our ability to maintain and/or enter into new corporate collaborations regarding these technologies, which would materially adversely affect our business, financial position and results of operations.

Enacted and future legislation may increase the difficulty and cost for us to obtain marketing approval of and commercialize our product candidates and may affect the prices we may set.

In the United States, the European Union and some other foreign jurisdictions, there have been a number of legislative and regulatory changes and proposed changes regarding the healthcare system. These changes could prevent or delay marketing approval of our product candidates, restrict or regulate post-approval activities and affect our ability to profitably sell any products for which we obtain marketing approval.

In the United States, the Medicare Prescription Drug, Improvement, and Modernization Act of 2003, or the Medicare Modernization Act, changed the way Medicare covers and pays for pharmaceutical products. The legislation expanded Medicare coverage for drug purchases by the elderly and introduced a new reimbursement methodology based on average sale prices for physician-administered drugs. In addition, this legislation provided authority for limiting the number of drugs that will be covered in any therapeutic class. Cost-reduction initiatives and other provisions of this legislation could decrease the coverage and price that we receive for any approved products. While the Medicare Modernization Act applies only to drug benefits for Medicare beneficiaries, private payors often follow Medicare coverage policy and payment limitations in setting their own reimbursement rates. Therefore, any reduction in reimbursement that results from the Medicare Modernization Act may result in a similar reduction in payments from private payors.

More recently, in March 2010, President Obama signed into law the Health Care Reform Law, a sweeping law intended to broaden access to health insurance, reduce or constrain the growth of healthcare spending, enhance remedies against fraud and abuse, add new transparency requirements for health care and health insurance industries, impose new taxes and fees on the health industry and impose additional health policy reforms. Effective October 1, 2010, the Health Care Reform Law revises the definition of “average manufacturer price” for reporting purposes, which could increase the amount of Medicaid drug rebates to states. Further, the new law imposes a significant annual fee on companies that manufacture or import branded prescription drug products. Substantial new provisions affecting compliance have also been enacted, which may affect our business practices with health care practitioners. We will not know the full effects of the Health Care Reform Law until applicable federal and state agencies issue regulations or guidance under the new law. Although it is too early to determine the effect of the Health Care Reform Law, the new law appears likely to continue the pressure on pharmaceutical pricing, especially under the Medicare program, and may also increase our regulatory burdens and operating costs.

Both in the US and in the EU, legislative and regulatory proposals have been made to expand post-approval requirements and restrict sales and promotional activities for pharmaceutical products. We are not sure whether additional legislative changes will be enacted, or whether the regulations, guidance or interpretations will be changed, or what the impact of such changes on the marketing approvals of our product candidates, if any, may be.

In the area of companion diagnostics, FDA officials indicated in 2010 that the agency planned to issue two guidances in this area. The FDA issued one draft guidance in July 2011, and the FDA plans to finalize this guidance in 2013. The FDA has yet to issue a second draft guidance and may decide not to issue a second draft guidance or finalize the existing draft guidance. The FDA’s issuance of a final guidance, or issuance of additional draft guidance, could affect our development of in vitro companion diagnostics and the applicable regulatory requirements. In

addition, increased scrutiny by the U.S. Congress of the FDA’s approval process may significantly delay or prevent marketing approval, as well as subject us to more stringent product labeling and post-marketing testing and other requirements.

In the EU, Regulation (EC) 1901/2006, the so called Paediatric Regulation, came into force in January 2007 and introduced considerable changes into the regulatory environment for pediatric medicines. The effects of this regulation are still not fully known. Additionally, an official guideline is being developed which addresses the development of medicinal products for the treatment of Duchenne and Becker muscular dystrophy. This guideline is planned to be adopted during the development of our compounds and may have an effect on the regulatory process for gaining market access in the EU.

Our relationships with customers and payors will be subject to applicable anti-kickback, fraud and abuse and other healthcare laws and regulations, which could expose us to criminal sanctions, civil penalties, contractual damages, reputational harm and diminished profits and future earnings.

Healthcare providers, physicians and others play a primary role in the recommendation and prescription of any products for which we obtain marketing approval. Our future arrangements with third-party payors and customers may expose us to broadly applicable fraud and abuse and other healthcare laws and regulations, primarily in the United States, that may constrain the business or financial arrangements and relationships through which we market, sell and distribute our products for which we obtain marketing approval. Restrictions under applicable healthcare laws and regulations, include the following:

Efforts to ensure that our business arrangements with third parties will comply with applicable healthcare laws and regulations will involve substantial costs. It is possible that governmental authorities will conclude that our business practices may not comply with current or future statutes, regulations or case law involving applicable fraud and abuse or other healthcare laws and regulations. If our operations are found to be in violation of any of these laws or any other governmental regulations that may apply to us, we may be subject to significant civil, criminal and administrative penalties, damages, fines, exclusion from U.S. government funded healthcare programs, such as Medicare and Medicaid, and the curtailment or restructuring of our operations. If any of the physicians or other providers or entities with whom we expect to do business with are found to be not in compliance with applicable laws, they may be subject to criminal, civil or administrative sanctions, including exclusions from government funded healthcare programs.

We operate in highly competitive and rapidly changing industries, which may result in others discovering, developing or commercializing competing products before or more successfully than we do.

The biopharmaceutical and pharmaceutical industries are highly competitive and subject to significant and rapid technological change. Our success is highly dependent on our ability to discover, develop and obtain marketing approval for new and innovative products on a cost-effective basis and to market them successfully. In doing so, we face and will continue to face intense competition from a variety of businesses, including large, fully integrated pharmaceutical companies, specialty pharmaceutical companies and biopharmaceutical companies, academic institutions, government agencies and other private and public research institutions in Europe, the United States and other jurisdictions. These organizations may have significantly greater resources than we do and conduct similar research, seek patent protection and establish collaborative arrangements for research, development, manufacturing and marketing of products that compete with our product candidates.

We believe that our key competitor in DMD is Sarepta Therapeutics, Inc., or Sarepta, a U.S. company focused on the development of their lead product candidate eteplirsen. Eteplirsen is currently in Phase II trials in DMD and employs the same exon 51 skipping approach as drisapersen. Sarepta may be in discussions with the FDA for accelerated approval of eteplirsen, which if granted, could place us at a competitive disadvantage. Even without accelerated approval, depending on the overall clinical profile, efficacy and commercialization of eteplirsen, Sarepta may render our development and discovery efforts in the area of DMD uncompetitive. Other companies are also developing alternative therapeutic approaches to the treatment of DMD. These approaches may be used as complementary to our products targeting DMD, but they could also be competitive.

In addition, GSK may decide to market and sell products that compete with the product candidates that we have agreed to license to it, and any competition by GSK could also have a material adverse effect on our future business, financial condition and results of operations.

The highly competitive nature of and rapid technological changes in the biotechnology and pharmaceutical industries could render our product candidates or our technology obsolete or non-competitive. Our competitors may, among other things:

Should any of these factors occur, our business, financial condition and results of operations could be materially adversely affected.

We rely on obtaining and maintaining orphan drug status for market exclusivity. Orphan drug status may not ensure that we have market exclusivity in a particular market, and we could lose orphan market exclusivity if another drug is approved first using the same method of action or demonstrates clinical superiority.

All of our DMD compounds have been granted orphan drug status by the FDA and EMA. If drisapersen or our other product candidates were to lose orphan drug status or the marketing exclusivity that it provides, our business and results of operations could be materially adversely affected. In the United States, a product candidate with orphan drug status qualifies for market exclusivity for seven years after FDA approval, unless a chemically identical competing product for the same indication is proved to be “clinically superior,” that is, safer, more effective or significantly more convenient. Thus, if drisapersen is granted regulatory approval in the United States, the FDA may not approve a competing generic product during the market exclusivity period; however, a chemically dissimilar product such as Sarepta’s eteplirsen would not be affected by drisapersen’s U.S. market exclusivity and could similarly obtain market exclusivity in the United States if it were to receive FDA approval.

In Europe, EMA regulations provide ten-year marketing exclusivity in Europe for orphan drugs, subject to certain exceptions, including the demonstration of “clinically relevant superiority” by a similar medicinal product. EMA orphan marketing exclusivity applies to drug products for the same indication that use the same method of action but can be chemically dissimilar. Eteplirsen has been granted orphan drug designation in the European Union. If Sarepta were to obtain marketing approval from the EMA for eteplirsen before drisapersen is approved by the EMA, Sarepta could have the benefit of orphan drug marketing exclusivity to our detriment because both products use the same method of action (exon skipping) for patients with DMD. Drisapersen would have to demonstrate a clinically relevant advantage over eteplirsen (in efficacy, safety and/or pharmacokinetics) in order to defeat such market exclusivity in Europe. If drisapersen is approved by the EMA before eteplirsen, eteplirsen could defeat drisapersen’s market exclusivity in Europe by demonstrating a clinically relevant advantage.

The successful commercialization of our product candidates will depend in part on the extent to which governmental authorities and health insurers establish adequate reimbursement levels and pricing policies.

The successful commercialization of our product candidates will depend, in part, on the extent to which third-party coverage and reimbursement for our products will be available from government and health administration authorities, private health insurers and other third-party payors.

These bodies may deny or revoke the reimbursement status of a given drug product or establish prices for new or existing marketed products at levels that are too low to enable us to realize an appropriate return on our investment in product development. Obtaining and maintaining reimbursement status is time-consuming and costly. Significant uncertainty exists as to the reimbursement status of newly approved medical products. Furthermore, rules and regulations regarding reimbursement change frequently, in some cases at short notice, and we believe that changes in these rules and regulations are likely. In addition, many governments and health insurers are increasingly attempting to manage healthcare costs by limiting both coverage and the level of reimbursement of new products. As a result, they may not cover or provide adequate payment for our future products.

The unavailability or inadequacy of third-party coverage and reimbursement could have a material adverse effect on the market acceptance of our product candidates and the future revenues we may expect to receive from those products. In addition, we are unable to predict what additional legislation or regulation relating to the healthcare industry or third-party coverage and reimbursement may be enacted in the future, or what effect such legislation or regulation would have on our business.

Our products may not gain market acceptance, in which case we may not be able to generate product revenues, which will materially adversely affect our business, financial condition and results of operations.

Even if the EMA, the FDA or any other regulatory authority approves the marketing of any product candidates that we develop on our own or with a collaboration partner, physicians, healthcare providers, patients or the medical community may not accept or use them. If these products do not achieve an adequate level of acceptance, we may not generate significant product revenues or any profits from operations. The degree of market acceptance of any of our product candidates will depend on a variety of factors, including:

If our product candidates fail to gain market acceptance, this will have a material adverse impact on our ability to generate revenues to provide a satisfactory, or any, return on our investments. Even if some products achieve market acceptance, the market may prove not to be large enough to allow us to generate significant revenues.

Adverse events in the field of RNA modulation therapy could damage public perception of our product candidates and negatively affect our business.

The commercial success of our products will depend in part on public acceptance of the use of RNA modulation therapy for the treatment of human diseases. Adverse events in clinical trials of our product candidates or in clinical trials of others developing RNA-modulating products and the resulting publicity, as well as any other adverse events in the field of RNA modulation therapy that may occur in the future, could result in a decrease in demand for any products that we may develop. For example, a recent case report described a case of renal damage in a healthy volunteer enrolled in a clinical trial of a different AON compound developed by a different company. If public perception is influenced by claims that RNA modulation therapy is unsafe, our products may not be accepted by the general public or the medical community.

Future adverse events in RNA modulation therapy or the biopharmaceutical industry could also result in greater governmental regulation, stricter labeling requirements and potential regulatory delays in the testing or approvals of our products. Any increased scrutiny could delay or increase the costs of obtaining regulatory approval for our product candidates.

We have never commercialized a product candidate before and may lack the necessary expertise, personnel and resources to successfully commercialize our products on our own or together with suitable partners.

We have never commercialized a product candidate, and we currently have no sales force, marketing or distribution capabilities. To achieve commercial success for drisapersen and other product candidates that GSK licenses under our collaboration, we will rely on GSK. For product candidates for which we retain commercialization rights, we will have to develop our own sales, marketing and supply organization or outsource these activities to a third party.

Factors that may affect our ability to commercialize our product candidates on our own include recruiting and retaining adequate numbers of effective sales and marketing personnel, obtaining access to or persuading adequate numbers of physicians to prescribe our drug candidates and other unforeseen costs associated with creating an independent sales and marketing organization. Developing a sales and marketing organization will be expensive and time-consuming and could delay the launch of our product candidates. We may not be able to build an effective sales and marketing organization. If we are unable to build our own distribution and marketing capabilities or to find suitable partners for the commercialization of our product candidates, we may not generate revenues from them or be able to reach or sustain profitability.

We may become liable for claims under the collaboration agreement with GSK or be unable to successfully enforce claims against counterparties.

Our collaboration agreement with GSK contains a liability and indemnification provision under which we may claim damages from GSK and under which GSK may claim damages from us, in each case in connection with the other party’s performance of its obligations under the collaboration. In the event we need to claim damages from any of our counterparties to any agreement, we may not receive payments covering our damages in full, because the applicable provision limits the payment to a certain amount, is unenforceable for any reason or the counterparty is unable to pay (due to insolvency or otherwise). Although in many cases we try to limit our liability, such limitations may not be effective in the event that we need to pay damages, and we nevertheless could become liable to make substantial payments, which would have a material adverse effect on our business, financial condition and results of operations.

If we fail to maintain our current strategic relationship with LUMC our business, commercialization prospects and financial condition may be materially adversely affected.

We have an exclusive worldwide license from Leiden University Medical Center, or LUMC, for the application of LUMC’s proprietary RNA modulation exon-skipping technology to develop treatments for DMD, other neuromuscular disorders and indications outside the field of neuromuscular disorders. These intellectual property rights have been the basis of our research so far and the development of treatments targeting DMD. The continuation of a good relationship with LUMC is essential for our business prospects. If our relationship with LUMC were to deteriorate or LUMC were to challenge our use of its intellectual property or our calculations of the payments we owe under our agreement, our business, financial condition, commercialization prospects and results of operations could be materially adversely affected.

If we fail to enter into new strategic relationships our business, financial condition, commercialization prospects and results of operations may be materially adversely affected.

Our product development programs and the potential commercialization of our product candidates will require substantial additional cash to fund expenses. Therefore, in addition to our relationships with GSK and LUMC, for some of our product candidates, we may decide to enter into new collaborations with pharmaceutical or biopharmaceutical companies for the development and potential commercialization of those product candidates.

We face significant competition in seeking appropriate collaborators. Collaborations are complex and time-consuming to negotiate and document. We may also be restricted under existing and future collaboration agreements from entering into agreements on certain terms with other potential collaborators. We may not be able to negotiate collaborations on acceptable terms, or at all. If that were to occur, we may have to curtail the development of a particular product candidate, reduce or delay its development program or one or more of our other development programs, delay its potential commercialization or reduce the scope of our sales or marketing activities, or increase our expenditures and undertake development or commercialization activities at our own expense. If we elect to increase our expenditures to fund development or commercialization activities on our own, we may need to obtain additional capital, which may not be available to us on acceptable terms or at all. If we do not have sufficient funds, we will not be able to bring our product candidates to market and generate product revenue. If we do

enter into a new collaboration agreement, we could be subject to the following risks, each of which may materially harm our business, commercialization prospects and financial condition:

We rely on third parties to provide services in connection with our preclinical and clinical development programs. The inadequate performance by or loss of any of these service providers could affect our product candidate development.

We rely on GSK to conduct clinical trials for the DMD compounds it has licensed from us under our collaboration; and we rely on other third parties, including CROs, medical institutions, clinical investigators and contract laboratories, to conduct significant portions of our preclinical and clinical trials. Although we oversee these activities to ensure compliance with our quality standards, budgets and timelines, we have had and will continue to have less control over the conduct of the clinical trials, the timing and completion of the trials, the required reporting of adverse events and the management of data developed through the trials than potentially would be the case if we relied entirely upon our own staff. Such third parties may have staffing difficulties, may undergo changes in priorities or may become financially distressed, adversely affecting the management of the clinical trials.

Problems with the timeliness or quality of the work of third parties may lead us to seek to terminate the relationship and use an alternative service provider. However, making this change may be costly and may delay the trials, and contractual restrictions may make such a change difficult or even impossible. In addition, it may be very challenging, and in some cases impossible, to find a replacement service provider that can conduct our trials in an acceptable manner and at an acceptable cost. In addition, if such third parties fail to comply with regulations regarding clinical trials and laboratory practices and other regulations of the EMA, FDA or other regulatory authorities, we may experience serious delays to our clinical trials, have to suspend clinical trials or lose the regulatory approval for a specific product. Any such failure could give rise to a material interruption in the development of the product and have a material adverse effect on our commercial potential.

We currently rely on third-party suppliers and other third parties for production of our product candidates and our dependence on these third parties may impair the advancement of our research and development programs and the development of our product candidates.

Currently, we develop and manufacture the drug product for our initial preclinical studies using standardized manufacturing processes in our own laboratories. We currently rely on and expect to continue to rely on third parties for the supply of raw materials and to manufacture drug

supplies for clinical trials and commercial quantities of our products and drug candidates. GSK is responsible for the production of product candidates that it licenses under our collaboration; and we are responsible for production of product candidates for which GSK has not exercised its option under our collaboration, to which we have retained rights or that are outside of the GSK collaboration. For the foreseeable future, we expect to continue to rely on such third parties.

Reliance on third-party providers may expose us to more risk than if we were to manufacture product candidates ourselves. We are obliged to work with manufacturing companies and third party suppliers that are licensed by the EMA, the FDA or other regulatory authorities and that comply with EMA, FDA or other regulatory authorities’ laws and regulations on an ongoing basis. We do not have control over a third-party manufacturer’s compliance with these laws, regulations and applicable cGMP standards and other laws and regulations, such as those related to environmental health and safety matters. Any failure to achieve and maintain compliance with these laws, regulations and standards could subject us to the risk that we may have to suspend the manufacturing of our product candidates or that obtained approvals could be revoked, which would adversely affect our business and reputation. Furthermore, third-party providers may breach existing agreements they have with us because of factors beyond our control. They may also terminate or refuse to renew their agreement because of their own financial difficulties or business priorities, at a time that is costly or otherwise inconvenient for us. If we were unable to find adequate replacement or another acceptable solution in time, our clinical trials could be delayed or our commercial activities could be harmed.

While we generally contract with multiple suppliers of raw materials, drug substances, drug product formulation and filling, for each specific AON there is only one contractor for drug substance manufacture and one contractor for drug product manufacture. In addition, we have only a single contractor for the packaging and distribution of product for clinical trials. While we believe we have limited the risk of interruption of production delays because our manufacturing process is highly standardized and therefore we believe that a contractor for one AON product candidate could be brought online to manufacture another AON product candidate, we may incur delays in qualifying an alternative manufacturer for a new compound. Any such delay could delay our clinical trials or have an adverse impact on any commercial activities.

In addition, the fact that we are dependent on GSK, our suppliers and other third parties for the manufacture, filling, storage and distribution of our product candidates means that we are subject to the risk that the products may have manufacturing defects that we have limited ability to prevent or control. The sale of products containing such defects could adversely affect our business, financial condition and results of operations.

Growth in the costs and expenses of components or raw materials may also adversely influence our business, financial condition and results of operations. Supply sources could be interrupted from time to time and, if interrupted, that supplies could be resumed (whether in part or in whole) within a reasonable timeframe and at an acceptable cost or at all.

Our business will be adversely affected if we are unable to gain access to relevant intellectual property rights of third parties, or if our licensing partners terminate our rights to license in relevant intellectual property rights.

We currently rely, and may in the future rely, on certain intellectual property rights licensed from third parties to protect our technology. In particular, we have entered into a collaboration

arrangement with LUMC for the reciprocal licensing of our and LUMC’s individual and joint intellectual property rights in relation to certain patent rights and know-how rights, which have been the basis of our research and development of treatment targeting DMD. Pursuant to this agreement with LUMC, we have an exclusive worldwide license for the exploitation of key intellectual property rights in this respect. Our intellectual property portfolio for DMD consists of patents and patent applications licensed from LUMC, patents and patent applications for which we and LUMC are joint owners and patents and patent applications that we own. LUMC retains full ownership of certain patents and patent applications which we have licensed under the agreement.

We have the responsibility to maintain and control the intellectual property portfolio licensed from LUMC, however, the licensed rights may not be adequately maintained by LUMC. In addition, our licensed rights may be suspended, terminated or otherwise lost in consequence of a breach of the agreement with LUMC or due to other relevant facts and circumstances such as insolvency of the licensor. Our ability to comply with our contractual obligations towards LUMC may be affected by factors that we can only partially influence or control.

If LUMC were to terminate the license, we would be prevented from continuing our use of this technology in clinical trials or, if our products are approved for marketing, from using this technology in products that could be sold commercially. The loss of rights under this license could preclude us from further developing, commercializing and marketing our products, which would have a material adverse effect on our business, financial condition, results of operations and prospects.

We rely on patents and other intellectual property rights to protect our product candidates and technologies, the enforcement, defense and maintenance of which may be challenging and costly. Failure to enforce or protect these rights adequately could harm our ability to compete and impair our business.

Our commercial success depends in part on obtaining and maintaining patents and other forms of intellectual property rights for our product candidates, methods used to manufacture those products and the methods for treating patients using those products, or on licensing in such rights. Failure to protect or to obtain, maintain or extend adequate patent and other intellectual property rights could materially adversely affect our ability to develop and market our products and product candidates.

Issued patents covering one or more of our products could be found invalid or unenforceable if challenged in court.

To protect our competitive position, we may from time to time need to resort to litigation in order to enforce or defend any patents or other intellectual property rights owned by or licensed to us, or to determine or challenge the scope or validity of patents or other intellectual property rights of third parties. For example, in 2009, AVI Biopharma Inc. (now Sarepta) filed an opposition against EP ’249, one of our patents, with the European Patent Office, or EPO, requesting revocation of the patent as granted, alleging, among other things, lack of novelty, inventive step and sufficiency of disclosure. The EPO Opposition Division, presiding in oral proceedings on November 16, 2011 in Munich, Germany, maintained the EP ’249 patent in an amended form. We believe that the patent as maintained in amended form by the EPO Opposition Division still provides protection for our lead product candidate drisapersen. We and

Sarepta both have the right to appeal the written decision of the EPO until June 15, 2013. We intend to appeal the written decision of the EPO. For additional information please see “Business—Intellectual property—Opposition proceedings against EP ’249.” As enforcement of intellectual property rights is difficult, unpredictable and expensive, we may fail in enforcing our rights—in which case our competitors may be permitted to use our technology without being required to pay us any license fees. In addition, however, litigation involving our patents carries the risk that one or more of our patents will be held invalid (in whole or in part, on a claim-by-claim basis) or held unenforceable. Such an adverse court ruling could allow third parties to commercialize our products or our platform technology, and then compete directly with us, without payment to us.

If we were to initiate legal proceedings against a third party to enforce a patent covering one of our products, the defendant could counterclaim that our patent is invalid and/or unenforceable. In patent litigation in the United States or in Europe, defendant counterclaims alleging invalidity and/or unenforceability are commonplace. Grounds for a validity challenge could be an alleged failure to meet any of several statutory requirements, for example, lack of novelty, obviousness or non-enablement. Grounds for an unenforceability assertion could be an allegation that someone connected with prosecution of the patent withheld relevant information from the U.S. Patent and Trademark Office, or made a misleading statement, during prosecution. The outcome following legal assertions of invalidity and unenforceability during patent litigation is unpredictable. With respect to the validity question, for example, we cannot be certain that there is no invalidating prior art, of which we and the patent examiner were unaware during prosecution. If a defendant were to prevail on a legal assertion of invalidity and/or unenforceability, we would lose at least part, and perhaps all, of the patent protection on one or more of our products or certain aspects of our platform technology. Such a loss of patent protection could have a material adverse impact on our business. Patents and other intellectual property rights also will not protect our technology if competitors design around our protected technology without infringing our patents or other intellectual property rights.

Intellectual property rights of third parties could adversely affect our ability to commercialize our product candidates, such that we could be required to litigate or obtain licenses from third parties in order to develop or market our product candidates. Such litigation or licenses could be costly or not available on commercially reasonable terms.

Our competitive position may suffer if patents issued to third parties or other third party intellectual property rights cover our products or elements thereof, our manufacture or uses relevant to our development plans. In such cases, we may not be in a position to develop or commercialize products or drug candidates unless we successfully pursue litigation to nullify or invalidate the third party intellectual property right concerned, or enter into a license agreement with the intellectual property right holder, if available on commercially reasonable terms. In addition, we are aware of issued patents and pending patent applications held by third parties that may be construed as covering some of our product candidates, in particular with respect to PRO045 or PRO053. We believe that if such patents or patent applications (if issued as currently pending) were asserted against us, we would have defenses against such claims, including defenses of patent invalidity and unenforceability. However, if such defenses were not successful and such patents were successfully asserted against us such that they are found to be valid and enforceable, and infringed by our product candidates, unless we obtain a license to such patents, which may not be available on commercially reasonable terms or at all, we could be prevented

from continuing to develop or commercialize our products. We could also be required to pay substantial damages.

It is also possible that we failed to identify relevant patents or applications. For example, U.S. applications filed before November 29, 2000 and certain U.S. applications filed after that date that will not be filed outside the United States remain confidential until patents issue. Patent applications in the United States and elsewhere are published approximately 18 months after the earliest filing for which priority is claimed, with such earliest filing date being commonly referred to as the priority date. Therefore, patent applications covering our products or platform technology could have been filed by others without our knowledge. Additionally, pending patent applications which have been published can, subject to certain limitations, be later amended in a manner that could cover our platform technologies, our products or the use of our products.

Third party intellectual property right holders, including our competitors, may actively bring infringement claims against us. The granting of orphan drug status in respect of any of our product candidates does not guarantee our freedom to operate and is separate from our risk of possible infringement of third parties’ intellectual property rights. We may not be able to successfully settle or otherwise resolve such infringement claims. If we are unable to successfully settle future claims on terms acceptable to us, we may be required to engage or continue costly, unpredictable and time-consuming litigation and may be prevented from or experience substantial delays in marketing our products.

If we fail in any such dispute, in addition to being forced to pay damages, we or our licensees may be temporarily or permanently prohibited from commercializing any of our product candidates that are held to be infringing. We might, if possible, also be forced to redesign drug candidates so that we no longer infringe the third party intellectual property rights. Any of these events, even if we were ultimately to prevail, could require us to divert substantial financial and management resources that we would otherwise be able to devote to our business.

Intellectual property litigation could cause us to spend substantial resources and distract our personnel from their normal responsibilities.

Even if resolved in our favor, litigation or other legal proceedings relating to intellectual property claims may cause us to incur significant expenses and could distract our technical and management personnel from their normal responsibilities. In addition, there could be public announcements of the results of hearings, motions or other interim proceedings or developments and if securities analysts or investors perceive these results to be negative, we could have a substantial adverse effect on the price of our ordinary shares. Such litigation or proceedings could substantially increase our operating losses and reduce our resources available for development activities. We may not have sufficient financial or other resources to adequately conduct such litigation or proceedings. Some of our competitors may be able to sustain the costs of such litigation or proceedings more effectively than we can because of their substantially greater financial resources. Uncertainties resulting from the initiation and continuation of patent litigation or other proceedings could have a material adverse effect on our ability to compete in the marketplace.

We enjoy only limited geographical protection with respect to certain patents and may face difficulties in certain jurisdictions, which may diminish the value of intellectual property rights in those jurisdictions.

We generally file our first patent application (i.e. priority filing) at the European Patent Office (EPO). International applications under the Patent Cooperation Treaty, or PCT, are usually filed within twelve months after the priority filing. Based on the PCT filing, national and regional patent applications may be filed in the United States, Australia, New Zealand, Japan, and Canada and all European Patent Convention, or EPC, member states by filing at the EPO and, depending on the individual case, also in any or all of, inter alia, China, India, Singapore and Israel. We have so far not filed for patent protection in all national and regional jurisdictions where such protection may be available. In addition, we may decide to abandon national and regional patent applications before grant. Finally, the grant proceeding of each national/regional patent is an independent proceeding which may lead to situations in which applications might in some jurisdictions be refused by the relevant registration authorities, while granted by others. It is also quite common that depending on the country, the scope of patent protection may vary for the same drug candidate and/or technology.

The laws of some jurisdictions do not protect intellectual property rights to the same extent as the laws in the United States and the European Union, and many companies have encountered significant difficulties in protecting and defending such rights in such jurisdictions. If we or our licensors encounter difficulties in protecting, or are otherwise precluded from effectively protecting, the intellectual property rights important for our business in such jurisdictions, the value of these rights may be diminished and we may face additional competition from others in those jurisdictions.

Many countries have compulsory licensing laws under which a patent owner may be compelled to grant licenses to third parties. In addition, many countries limit the enforceability of patents against government agencies or government contractors. In these countries, the patent owner may have limited remedies, which could materially diminish the value of such patent. If we or any of our licensors is forced to grant a license to third parties with respect to any patents relevant to our business, our competitive position may be impaired and our business and results of operations may be adversely affected.

Intellectual property rights do not necessarily address all potential threats to our competitive advantage.

The degree of future protection afforded by our intellectual property rights is uncertain because intellectual property rights have limitations, and may not adequately protect our business, or permit us to maintain our competitive advantage. The following examples are illustrative:

Changes in patent laws or patent jurisprudence could diminish the value of patents in general, thereby impairing our ability to protect our products.

As is the case with other biopharmaceutical companies, our success is heavily dependent on intellectual property, particularly patents. Obtaining and enforcing patents in the biopharmaceutical industry involve both technological complexity and legal complexity. Therefore, obtaining and enforcing biopharmaceutical patents is costly, time-consuming and inherently uncertain. In addition, the America Invents Act (AIA) has been recently enacted in the United States, resulting in significant changes to the U.S. patent system. The U.S. Supreme Court has ruled on several patent cases in recent years, either narrowing the scope of patent protection available in certain circumstances or weakening the rights of patent owners in certain situations. In addition to increasing uncertainty with regard to our ability to obtain patents in the future, this combination of events has created uncertainty with respect to the value of patents, once obtained. Depending on decisions by the U.S. Congress, the federal courts, and the U.S. Patent and Trademark Office, the laws and regulations governing patents could change in unpredictable ways that could weaken our ability to obtain new patents or to enforce our existing patents and patents that we might obtain in the future. Similarly, the complexity and uncertainty of European patent laws has also increased in recent years. For example, the EPC was amended in April 2010 by limiting the time permitted for filing divisional applications. In addition, the EP patent system is relatively stringent in the type of amendments that are allowed during prosecution. These changes could limit our ability to obtain new patents in the future that may be important for our business.

Confidentiality agreements with employees and others may not adequately prevent disclosure of trade secrets and protect other proprietary information.

We consider proprietary trade secrets and/or confidential know-how and unpatented know-how to be important to our business. We may rely on trade secrets and/or confidential know-how to protect our technology, especially where patent protection is believed to be of limited value. However, trade secrets and/or confidential know-how are difficult to maintain as confidential.

To protect this type of information against disclosure or appropriation by competitors, our policy is to require our employees, consultants, contractors and advisors to enter into confidentiality

agreements with us. However, current or former employees, consultants, contractors and advisers may unintentionally or willfully disclose our confidential information to competitors, and confidentiality agreements may not provide an adequate remedy in the event of unauthorized disclosure of confidential information. Enforcing a claim that a third party obtained illegally and is using trade secrets and/or confidential know-how is expensive, time consuming and unpredictable. The enforceability of confidentiality agreements may vary from jurisdiction to jurisdiction.

Failure to obtain or maintain trade secrets and/or confidential know-how trade protection could adversely affect our competitive position. Moreover, our competitors may independently develop substantially equivalent proprietary information and may even apply for patent protection in respect of the same. If successful in obtaining such patent protection, our competitors could limit our use of our trade secrets and/or confidential know-how.

Under certain circumstances and to guarantee our freedom to operate, we may also decide to publish some know-how to prevent others from obtaining patent rights covering such know-how.

Our information technology systems could face serious disruptions that could adversely affect our business.

Our information technology and other internal infrastructure systems, including corporate firewalls, servers, leased lines and connection to the Internet, face the risk of systemic failure that could disrupt our operations. A significant disruption in the availability of our information technology and other internal infrastructure systems could cause interruptions in our collaborations with our partners and delays in our research and development work.

Our future growth and ability to compete depends on retaining our key personnel and recruiting additional qualified personnel.

Our success depends upon the continued contributions of our key management, scientific and technical personnel, many of whom have substantial experience with or been instrumental for us and our unique RNA modulation therapy and related technologies. These key management individuals include the members of our management board consisting of Hans Schikan, our Chief Executive Officer; Berndt Modig, our Chief Financial Officer; Giles Campion, our Chief Medical Officer and Senior Vice President Research and Development; and Luc Dochez, our Chief Business Officer and Senior Vice President Business Development. The key members of our management team include Larry Bell, our Vice President of Regulatory Affairs; Judith van Deutekom, our Vice President Drug Discovery; Tina Flatau, our Vice President Alliances and Project Management; Paul van Hagen, our Senior Director Finance and Control; Richard Holslag, our Vice President Manufacturing; Sjef de Kimpe, our Vice President Early Drug Development; and Allison Morgan, our Vice President Clinical Development.

The loss of key managers and senior scientists could delay our research and development activities. In addition, the competition for qualified personnel in the biopharmaceutical and pharmaceutical field is intense, and our future success depends upon our ability to attract, retain and motivate highly-skilled scientific, technical and managerial employees. We face competition for personnel from other companies, universities, public and private research institutions and

other organizations. If our recruitment and retention efforts are unsuccessful in the future, it may be difficult for us to implement business strategy, which could have a material adverse effect on our business.

We expect to expand our development, regulatory and sales and marketing capabilities, and as a result, we may encounter difficulties in managing our growth, which could disrupt our operations.

We expect to experience significant growth in the number of our employees and the scope of our operations, particularly in the areas of drug development, regulatory affairs and sales and marketing. To manage our anticipated future growth, we must continue to implement and improve our managerial, operational and financial systems, expand our facilities and continue to recruit and train additional qualified personnel. Due to our limited financial resources and the limited experience of our management team in managing a company with such anticipated growth, we may not be able to effectively manage the expansion of our operations or recruit and train additional qualified personnel. The expansion of our operations may lead to significant costs and may divert our management and business development resources. Any inability to manage growth could delay the execution of our business plans or disrupt our operations.

The price of our ordinary shares may be volatile and may fluctuate due to factors beyond our control.

The share price of publicly traded emerging biopharmaceutical and drug discovery and development companies has been highly volatile and is likely to remain highly volatile in the future. The market price of our ordinary shares may fluctuate significantly due to a variety of factors, including:

In addition, the stock market in general has recently experienced extreme price and volume fluctuations that have often been unrelated or disproportionate to the operating performance of individual companies. Broad market and industry factors may materially affect the market price of companies’ stock, including our, regardless of actual operating performance.

There has been no public market for our ordinary shares prior to this offering, and an active market in the shares may not develop in which investors can resell our ordinary shares.

Prior to this offering there has been no public market for our ordinary shares. We cannot predict the extent to which an active market for our ordinary shares will develop or be sustained after this offering, or how the development of such a market might affect the market price for our ordinary shares. The initial public offering price of our ordinary shares in this offering will be agreed between us and the underwriters based on a number of factors, including market conditions in effect at the time of the offering, which may not be indicative of the price at which our shares will trade following completion of the offering. Investors may not be able to sell their shares at or above the initial public offering price.

Certain of our existing shareholders and members of our management board will continue to own a majority of our ordinary shares and as a result will be able to exercise significant control over us, and your interests may conflict with the interests of our existing shareholders.

Following completion of this offering, our existing shareholders are expected to own approximately % of our ordinary shares. Depending on the level of attendance at our general meetings of shareholders, these shareholders may be in a position to determine the outcome of decisions taken at any such general meeting. Any shareholder or group of shareholders controlling more than 50% of the capital present and voting at our general meetings of shareholders may control any shareholder resolution requiring a simple majority, including the appointment of supervisory board members, certain decisions relating to our capital structure, the approval of certain significant corporate transactions and amendments to our Articles of Association. Among other consequences, this concentration of ownership may have the effect of delaying or preventing a change in control and might therefore negatively affect the market price of our ordinary shares.

Future sales, or the possibility of future sales, of a substantial number of our ordinary shares could adversely affect the price of the shares and dilute shareholders.

Future sales of a substantial number of our ordinary shares, or the perception that such sales will occur, could cause a decline in the market price of our ordinary shares. Following the completion of this offering, we will have ordinary shares outstanding (assuming no exercise of the over-allotment option) based on ordinary shares outstanding as of , 2013. This includes the shares in this offering, which may be resold in the public market immediately without restriction, unless purchased by our affiliates. Approximately % of the shares outstanding will be held by existing shareholders. These shares will be subject to the lock-up agreements described in the “Underwriting” section of this prospectus. If, after the end of such lock-up agreements, these shareholders sell substantial amounts of shares in the public market, or the market perceives that such sales may occur, the market price of our ordinary shares and our ability to raise capital through an issue of equity securities in the future could be adversely affected. We also intend to enter into a registration rights agreement upon consummation of this offering pursuant to which we will agree under certain circumstances to file a registration statement to register the resale of the shares held by certain of our existing shareholders, as well as to cooperate in certain public offerings of such shares. In addition, we intend to register all ordinary shares that we may issue under our equity compensation plans. Once we register these ordinary shares, they can be freely sold in the public market upon issuance, subject to volume limitations applicable to affiliates and the lock-up agreements described in the “Underwriting” section of this prospectus.

Provisions of our Articles of Association or Dutch corporate law might deter acquisition bids for us that might be considered favorable and prevent or frustrate any attempt to replace or remove the then management board and supervisory board.

Certain provisions of our Articles of Association may make it more difficult for a third party to acquire control of us or effect a change in our management board or supervisory board. These provisions include: the authorization of a class of preference shares that may be issued to a friendly party; staggered four-year terms of our supervisory board members; a provision that our management board and supervisory board members may only be removed by the general meeting of shareholders by a two-thirds majority of votes cast representing more than 50% of our outstanding share capital (unless the removal was proposed by the supervisory board); and a requirement that certain matters, including an amendment of our Articles of Association, may only be brought to our shareholders for a vote upon a proposal by our management board that has been approved by our supervisory board.

We have adopted an anti-takeover measure pursuant to which our management board may, subject to supervisory board approval but without shareholder approval, issue (or grant the right to acquire) cumulative preferred shares. We may issue an amount of cumulative preferred shares up to 100% of our issued capital immediately prior to the issuance of such cumulative preferred shares. In such event, the cumulative preferred shares (or right to acquire cumulative preferred shares) will be issued to a separate, newly established foundation.

The cumulative preferred shares will be issued to the foundation for their nominal value, of which only 25% will be due upon issuance. The voting rights of our shares are based on nominal value and as we expect our shares to trade substantially in excess of nominal value, cumulative preferred shares issued at nominal value can obtain significant voting power for a substantially reduced price and thus be used as a defensive measure. These cumulative preferred shares will have both a liquidation and dividend preference over our ordinary shares and will accrue cash dividends at a fixed rate. The management board may issue these cumulative preferred shares to protect us from influences that do not serve our best interests and threaten to undermine our continuity, independence and identity. These influences may include a third-party acquiring a significant percentage of our ordinary shares, the announcement of a public offer for our ordinary shares, other concentration of control over our ordinary shares or any other form of pressure on us to alter our strategic policies. If the management board determines to issue the cumulative preferred shares to such a foundation, the foundation’s articles of association will provide that it will act to serve the best interests of us, our associated business and all parties connected to us, by opposing any influences that conflict with these interests and threaten to undermine our continuity, independence and identity. This foundation will be structured to operate independently of us.

If you purchase ordinary shares in this offering, you will suffer immediate dilution of your investment.

The initial public offering price of our ordinary shares is substantially higher than the pro forma net tangible book value per ordinary share. Therefore, if you purchase ordinary shares in this offering, you will pay a price per share that substantially exceeds our pro forma net tangible book value per ordinary share after this offering. To the extent outstanding options are

exercised, you will incur further dilution. Based on the initial public offering price of $ per share, you will experience immediate dilution of $ per share, representing the difference between our pro forma net tangible book value per share after giving effect to this offering and the initial public offering price. In addition, purchasers of ordinary shares in this offering will have contributed approximately % of the aggregate price paid by all purchasers of our ordinary shares but will own only approximately % of our ordinary shares outstanding after this offering. See “Dilution.”

We have broad discretion in the use of the net proceeds from this offering and may not use them effectively.

Our management will have broad discretion in the application of the net proceeds from this offering and could spend the proceeds in ways that do not improve our results of operations or enhance the value of our ordinary shares. The failure by our management to apply these funds effectively could result in financial losses that could have a material adverse effect on our business, cause the price of our ordinary shares to decline and delay the development of our product candidates. Pending their use, we may invest the net proceeds from this offering in a manner that does not produce income or that loses value.

We have not paid any dividends since our incorporation. Even if future operations lead to significant levels of distributable profits, we currently intend that any earnings will be reinvested in our business and that dividends will not be paid until we have an established revenue stream to support continuing dividends. Payment of future dividends to shareholders will in addition effectively be at the discretion of the management board, subject to the approval of the supervisory board after taking into account various factors including our business prospects, cash requirements, financial performance and new product development. In addition, payment of future dividends may be made only if our shareholders’ equity exceeds the sum of our paid-in and called-up share capital plus the reserves required to be maintained by Dutch law or by our Articles of Association. Accordingly, investors cannot rely on dividend income from our ordinary shares and any returns on an investment in our ordinary shares will likely depend entirely upon any future appreciation in the price of our ordinary shares.

Holders of our ordinary shares outside the Netherlands may not be able to exercise preemptive rights.

In the event of an increase in our share capital, holders of our ordinary shares are generally entitled under Dutch law to full preemptive rights, unless these rights are excluded either by a resolution of the general meeting of shareholders, or by a resolution of the management board (if the management board has been designated by the general meeting of shareholders for this purpose). See “Description of capital stock and Articles of Association—Comparison of Dutch corporate law and our Articles of Association and U.S. corporate law—Preemptive rights.” Certain holders of our ordinary shares outside the Netherlands, in particular U.S. holders of our ordinary shares, may not be able to exercise preemptive rights unless a registration statement under the Securities Act of 1933, as amended (Securities Act) is declared effective with respect to our ordinary shares issuable upon exercise of such rights or an exemption from the registration requirements is available.

Upon the consummation of this offering, we will be a Dutch public company with limited liability. The rights of our shareholders may be different from the rights of shareholders in companies governed by the laws of U.S. jurisdictions.

Upon the consummation of this offering, we will be a Dutch public company with limited liability (naamloze vennootschap). Our corporate affairs are governed by our Articles of Association and by the laws governing companies incorporated in the Netherlands. The rights of shareholders and the responsibilities of members of our management board and supervisory board may be different from the rights and obligations of shareholders in companies governed by the laws of U.S. jurisdictions. In the performance of its duties, our management board and supervisory board are required by Dutch law to consider the interests of our company, its shareholders, its employees and other stakeholders, in all cases with due observation of the principles of reasonableness and fairness. It is possible that some of these parties will have interests that are different from, or in addition to, your interests as a shareholder. See “Description of capital stock and Articles of Association—Corporate governance.”

We are not obligated to and do not comply with all the best practice provisions of the Dutch Corporate Governance Code. This may affect your rights as a shareholder.

As a Dutch company we are subject to the Dutch Corporate Governance Code, or DCGC. The DCGC contains both principles and best practice provisions for management boards, supervisory boards, shareholders and general meetings of shareholders, financial reporting, auditors, disclosure, compliance and enforcement standards. The DCGC applies to all Dutch companies listed on a government-recognized stock exchange, whether in the Netherlands or elsewhere, including the Nasdaq Global Stock Market, or Nasdaq. The principles and best practice provisions apply to our management board and our supervisory board (in relation to role and composition, conflicts of interest and independency requirements, board committees and remuneration), shareholders and the general meeting of shareholders (for example, regarding anti-takeover protection and our obligations to provide information to its shareholders) and financial reporting (such as external auditor and internal audit requirements). We do not comply with all the best practice provisions of the DCGC. See “Description of capital stock and Articles of Association—Dutch corporate governance.” This may affect your rights as a shareholder and you may not have the same level of protection as a shareholder in a Dutch company that fully complies with the DCGC.

We are incorporated under the laws of the Netherlands. Substantially all of our assets are located outside the United States. The majority of our directors reside outside the United States. As a result, it may not be possible for investors to effect service of process within the United States upon such persons or to enforce against them or us in U.S. courts, including judgments predicated upon the civil liability provisions of the federal securities laws of the United States.

rendered will be required to file its claim with a court of competent jurisdiction in the Netherlands. Such party may submit to the Dutch court the final judgment rendered by the U.S. court. If and to the extent that the Dutch court finds that the jurisdiction of the U.S. court has been based on grounds which are internationally acceptable and that proper legal procedures have been observed, the court of the Netherlands will, in principle, give binding effect to the judgment of the U.S. court, unless such judgment contravenes principles of public policy of the Netherlands. Dutch courts may deny the recognition and enforcement of punitive damages or other awards. Moreover, a Dutch court may reduce the amount of damages granted by a U.S. court and recognize damages only to the extent that they are necessary to compensate actual losses or damages. Enforcement and recognition of judgments of U.S. courts in the Netherlands are solely governed by the provisions of the Dutch Civil Procedure Code.

Based on the lack of a treaty as described above, U.S. investors may not be able to enforce against us or members of our management board or supervisory board, officers or certain experts named herein who are residents of the Netherlands or countries other than the United States any judgments obtained in U.S. courts in civil and commercial matters, including judgments under the U.S. federal securities laws.

We will be a foreign private issuer and, as a result, we will not be subject to U.S. proxy rules and will be subject to Exchange Act reporting obligations that, to some extent, are more lenient and less frequent than those of a U.S. domestic public company.

Upon consummation of this offering, we will report under the Securities Exchange Act of 1934, as amended, or the Exchange Act, as a non-U.S. company with foreign private issuer status. Because we qualify as a foreign private issuer under the Exchange Act and although we are subject to Dutch laws and regulations with regard to such matters and intend to furnish quarterly financial information to the SEC, we are exempt from certain provisions of the Exchange Act that are applicable to U.S. domestic public companies, including (i) the sections of the Exchange Act regulating the solicitation of proxies, consents or authorizations in respect of a security registered under the Exchange Act; (ii) the sections of the Exchange Act requiring insiders to file public reports of their stock ownership and trading activities and liability for insiders who profit from trades made in a short period of time; and (iii) the rules under the Exchange Act requiring the filing with the Securities and Exchange Commission (SEC) of quarterly reports on Form 10-Q containing unaudited financial and other specified information, or current reports on Form 8-K, upon the occurrence of specified significant events. In addition, foreign private issuers are not be required to file their annual report on Form 20-F until 120 days after the end of each fiscal year, while U.S. domestic issuers that are accelerated filers are required to file their annual report on Form 10-K within 75 days after the end of each fiscal year. Foreign private issuers are also exempt from the Regulation Fair Disclosure, aimed at preventing issuers from making selective disclosures of material information. As a result of the above, you may not have the same protections afforded to shareholders of companies that are not foreign private issuers.

As a foreign private issuer and as permitted by the listing requirements of Nasdaq, we will rely on certain home country governance practices rather than the corporate governance requirements of Nasdaq.

We will be a foreign private issuer. As a result, in accordance with the listing requirements of Nasdaq, we will rely on home country governance requirements and certain exemptions thereunder rather than relying on the corporate governance requirements of Nasdaq. In

accordance with Dutch law and generally accepted business practices, our articles of association do not provide quorum requirements generally applicable to general meetings of shareholders. To this extent, our practice varies from the requirement of Nasdaq Listing Rule 5620(c), which requires an issuer to provide in its bylaws for a generally applicable quorum, and that such quorum may not be less than one-third of the outstanding voting stock. Although we must provide shareholders with an agenda and other relevant documents for the general meeting of shareholders, Dutch law does not have a regulatory regime for the solicitation of proxies and the solicitation of proxies is not a generally accepted business practice in the Netherlands. For an overview of our corporate governance principles, see “Description of capital stock and Articles of Association—Corporate governance,” including the section describing the differences between the corporate governance requirements applicable to our ordinary shares to be listed on Nasdaq and the Dutch corporate governance requirements. Accordingly, you may not have the same protections afforded to shareholders of companies that are not foreign private issuers.

We may lose our foreign private issuer status which would then require us to comply with the Exchange Act’s domestic reporting regime and cause us to incur significant legal, accounting and other expenses.

We are a foreign private issuer and therefore we are not required to comply with all of the periodic disclosure and current reporting requirements of the Exchange Act applicable to U.S. domestic issuers. We may no longer be a foreign private issuer as of June 30, 2014 (the end of our second fiscal quarter in the fiscal year after this offering), which would require us to comply with all of the periodic disclosure and current reporting requirements of the Exchange Act applicable to U.S. domestic issuers as of January 1, 2015. In order to maintain our current status as a foreign private issuer, either (a) a majority of our ordinary shares must be either directly or indirectly owned of record by non-residents of the United States or (b)(i) a majority of our executive officers or directors may not be United States citizens or residents, (ii) more than 50 percent of our assets cannot be located in the United States and (iii) our business must be administered principally outside the United States. If we lost this status, we would be required to comply with the Exchange Act reporting and other requirements applicable to U.S. domestic issuers, which are more detailed and extensive than the requirements for foreign private issuers. We may also be required to make changes in our corporate governance practices in accordance with various SEC and Nasdaq rules. The regulatory and compliance costs to us under U.S. securities laws if we are required to comply with the reporting requirements applicable to a U.S. domestic issuer may be significantly higher than the cost we would incur as a foreign private issuer. As a result, we expect that a loss of foreign private issuer status would increase our legal and financial compliance costs and would make some activities highly time consuming and costly. We also expect that if we were required to comply with the rules and regulations applicable to U.S. domestic issuers, it would make it more difficult and expensive for us to obtain director and officer liability insurance, and we may be required to accept reduced coverage or incur substantially higher costs to obtain coverage. These rules and regulations could also make it more difficult for us to attract and retain qualified members of our supervisory board.

We are an “emerging growth company,” and we cannot be certain if the reduced reporting requirements applicable to “emerging growth companies” will make our ordinary shares less attractive to investors.

We are an “emerging growth company,” as defined in the JOBS Act. For as long as we continue to be an “emerging growth company,” we may take advantage of exemptions from various

reporting requirements that are applicable to other public companies that are not “emerging growth companies,” including not being required to comply with the auditor attestation requirements of Section 404 of the Sarbanes-Oxley Act of 2002, exemptions from the requirements of holding a nonbinding advisory vote on executive compensation and shareholder approval of any golden parachute payments not previously approved. As an “emerging growth company” we are required to report only two years of financial results and selected financial data compared to three and five years, respectively, for comparable data reported by other public companies. We may take advantage of these exemptions until we are no longer an “emerging growth company.” We could be an “emerging growth company” for up to five years, although circumstances could cause us to lose that status earlier, including if the market value of our ordinary shares held by non-affiliates exceeds $700 million as of any June 30 (the end of our second fiscal quarter) before that time, in which case we would no longer be an “emerging growth company” as of the following December 31 (our fiscal year end). We cannot predict if investors will find our ordinary shares less attractive because we may rely on these exemptions. If some investors find our ordinary shares less attractive as a result, there may be a less active trading market for our ordinary shares and the price of our ordinary shares may be more volatile.

If we fail to maintain an effective system of internal control over financial reporting, we may not be able to accurately report our financial results or prevent fraud. As a result, shareholders could lose confidence in our financial and other public reporting, which would harm our business and the trading price of our ordinary shares.

Effective internal controls over financial reporting are necessary for us to provide reliable financial reports and, together with adequate disclosure controls and procedures, are designed to prevent fraud. Any failure to implement required new or improved controls, or difficulties encountered in their implementation could cause us to fail to meet our reporting obligations. In addition, any testing by us conducted in connection with Section 404 of the Sarbanes-Oxley Act of 2002, or any subsequent testing by our independent registered public accounting firm, may reveal deficiencies in our internal controls over financial reporting that are deemed to be material weaknesses or that may require prospective or retroactive changes to our financial statements or identify other areas for further attention or improvement. Inferior internal controls could also cause investors to lose confidence in our reported financial information, which could have a negative effect on the trading price of our ordinary shares.

We will be required to disclose changes made in our internal controls and procedures on a quarterly basis and our management will be required to assess the effectiveness of these controls annually. However, for as long as we are an “emerging growth company” under the JOBS Act, our independent registered public accounting firm will not be required to attest to the effectiveness of our internal controls over financial reporting pursuant to Section 404. We could be an “emerging growth company” for up to five years. An independent assessment of the effectiveness of our internal controls could detect problems that our management’s assessment might not. Undetected material weaknesses in our internal controls could lead to financial statement restatements and require us to incur the expense of remediation.

If securities or industry analysts do not publish research, or publish inaccurate or unfavorable research, about our business, the price of our ordinary shares and our trading volume could decline.

The trading market for our ordinary shares will depend in part on the research and reports that securities or industry analysts publish about us or our business. Securities and industry analysts do not currently, and may never, publish research on our company. If no or too few securities or industry analysts commence coverage of our company, the trading price for our ordinary shares would likely be negatively affected. In the event securities or industry analysts initiate coverage, if one or more of the analysts who cover us downgrade our ordinary shares or publish inaccurate or unfavorable research about our business, the price of our ordinary shares would likely decline. If one or more of these analysts cease coverage of our company or fail to publish reports on us regularly, demand for our ordinary shares could decrease, which might cause the price of our ordinary shares and trading volume to decline.

We may be classified as a passive foreign investment company (a “PFIC”) in 2013 or any future years. If we are a PFIC for any taxable year, this could result in adverse U.S. federal income tax consequences to U.S. investors.

Under the Internal Revenue Code of 1986, as amended (the Code), we will be a PFIC for any taxable year in which, after the application of certain “look-through” rules with respect to subsidiaries, either (i) 75% or more of our gross income consists of “passive income,” or (ii) 50% or more of the average quarterly value of our assets consist of assets that produce, or are held for the production of, “passive income.” Passive income generally includes interest, dividends, rents, certain non-active royalties and capital gains. Whether we will be a PFIC in any year depends on the composition of our income and assets, and the relative fair market value of our assets from time to time, which we expect may vary substantially over time. Because (i) we currently own, and will own after the completion of this offering, a substantial amount of passive assets, including cash, and (ii) the values of our assets, including our intangible assets, that generate non-passive income for PFIC purposes, is uncertain and may vary substantially over time, it is uncertain whether we will be or will not be a PFIC in 2013 or any future years.

If we are a PFIC for any taxable year during which a U.S. investor holds ordinary shares, the U.S. investor may be subject to adverse tax consequences, including (i) the treatment of all or a portion of any gain on disposition as ordinary income, (ii) the application of a deferred interest charge on such gain and the receipt of certain dividends and (iii) compliance with certain reporting requirements.

For further discussion of the adverse U.S. federal income tax consequences of our classification as a PFIC, see “Taxation—U.S. federal income tax considerations for U.S. holders.”

This prospectus contains statements that constitute forward-looking statements. Many of the forward-looking statements contained in this prospectus can be identified by the use of forward-looking words such as “anticipate,” “believe,” “could,” “expect,” “should,” “plan,” “intend,” “estimate” and “potential,” among others.

Forward-looking statements appear in a number of places in this prospectus and include, but are not limited to, statements regarding our intent, belief or current expectations. Forward-looking statements are based on our management’s beliefs and assumptions and on information currently available to our management. Such statements are subject to risks and uncertainties, and actual results may differ materially from those expressed or implied in the forward-looking statements due to of various factors, including, but not limited to, those identified under the section entitled “Risk factors” in this prospectus. These risks and uncertainties include factors relating to:

Forward-looking statements speak only as of the date they are made, and we do not undertake any obligation to update them in light of new information or future developments or to release publicly any revisions to these statements in order to reflect later events or circumstances or to reflect the occurrence of unanticipated events.

We prepare our financial statements under IFRS as issued by the IASB. None of the financial statements included in this prospectus were prepared in accordance with generally accepted accounting principles in the United States. We maintain our books and records in euros. In this prospectus, translations from euros to U.S. dollars were made at the rate of €0.781 to $1.00, the official exchange rate quoted as of March 31, 2013 by the European Central Bank.

All amounts paid to us under our agreement with GSK are paid in British pounds. In this prospectus, translations from British pounds to euros

Pursuant to the Shareholders’ Agreement, all of our outstanding preferred shares will convert into our ordinary shares upon the consummation of this offering. The conversion rate for the preferred shares is calculated by reference to the original issue price of relevant preferred shares, adjusted for any stock splits, share distributions and, in the case of holders of Class A and Class B preferred shares, certain anti-dilution protections. The conversion rate immediately prior to the consummation of this offering will be one-to-one, and therefore all of our outstanding preferred shares will convert into an aggregate of 25,511,240 ordinary shares, which will result in us having ordinary shares outstanding after this offering. We refer to this as the Share Conversion. See “Related party transactions—Shareholders’ agreement.”

Prior to the consummation of this offering, we intend to convert from a private company with limited liability, Prosensa Holding B.V., to a public company with limited liability, Prosensa Holding N.V. The audited financial statements for the years ended and as of December 31, 2012 and 2011 and the unaudited financial statements for the three months ended and as of March 31, 2013 and 2012 are the financial statements for Prosensa Holding B.V.

The term “$” refers to U.S. dollars, the terms “£,” “GBP” and “British pounds” refer to the legal currency of the United Kingdom and the terms “€” or “euro” refer to the currency introduced at the start of the third stage of European economic and monetary union pursuant to the treaty establishing the European Community, as amended.

We expect to receive total estimated net proceeds of approximately $ (€ ), based on the midpoint of the range set forth on the cover page of this prospectus after deducting estimated underwriting discounts and commissions and expenses of the offering that are payable by us. Each $1.00 increase (decrease) in the public offering price per ordinary share would increase (decrease) our net proceeds, after deducting estimated underwriting discounts and commissions and expenses, by $ (€ ), assuming that the number of shares offered by us, as set forth on the cover of this prospectus, remains the same.

As of March 31, 2013, we had cash and cash equivalents of €36.1 million. We currently expect that we will use the net proceeds from this offering, together with our cash and cash equivalents on hand, as follows:

Our expected use of net proceeds from this offering represents our current intentions based upon our present plans and business condition. As of the date of this prospectus, we cannot predict with certainty all of the particular uses for the net proceeds to be received upon the completion of this offering or the amounts that we will actually spend on the uses set forth above. The amounts and timing of our actual use of net proceeds will vary depending on numerous factors, including our ability to obtain additional financing, the relative success and cost of our research, preclinical and clinical development programs, the amount and timing of additional revenues, if any, received from our collaboration with GSK and whether we enter into future collaborations. As a result, management will have broad discretion in the application of the net proceeds, and investors will be relying on our judgment regarding the application of the net proceeds of this offering. In addition, we might decide to postpone or not pursue other clinical trials or preclinical activities if the net proceeds from this offering and our other sources of cash are less than expected.

Based on our planned use of the net proceeds of this offering and our current cash and cash equivalents described above, we estimate that such funds will be sufficient to enable us to fund our operating expenses and capital expenditure requirements for at least the next months. We have based this estimate on assumptions that may prove to be incorrect, and we could use our available capital resources sooner than we currently expect.

Pending their use, we plan to invest the net proceeds from this offering in short- and intermediate-term interest-bearing obligations and certificates of deposit.

We have never paid or declared any cash dividends on our ordinary shares, and we do not anticipate paying any cash dividends on our ordinary shares in the foreseeable future. We intend to retain all available funds and any future earnings to fund the development and expansion of our business. Any future determination to pay dividends will be at the discretion of our supervisory board and will depend upon a number of factors, including our results of operations, financial condition, future prospects, contractual restrictions, restrictions imposed by applicable law and other factors our supervisory board deems relevant.

The table below sets forth our capitalization (defined as long-term debt and shareholders’ equity) as of March 31, 2013 derived from our unaudited consolidated financial statements included in this prospectus:

Investors should read this table in conjunction with our consolidated audited and condensed consolidated unaudited financial statements included in this prospectus as well as “Use of proceeds,” “Selected financial information” and “Management’s discussion and analysis of financial condition and results of operations.”

If you invest in our ordinary shares, your interest will be diluted to the extent of the difference between the initial public offering price per share and the net tangible book value per share after this offering.

At March 31, 2013, we had a net tangible book value of $14.5 million (€11.3 million), corresponding to a net tangible book value of $0.50 per share (€0.39 per share). Net tangible book value per share represents the amount of our total assets less our total liabilities, excluding goodwill and other intangible assets, divided by 29,002,298, the total number of our ordinary shares and preferred shares outstanding at March 31, 2013. Because the conversion of our preferred shares into ordinary shares will occur on a one-to-one basis, the Share Conversion will not result in additional dilution.

After giving effect to the sale by us of the ordinary shares offered by us in the offering, and assuming an offering price of $ per share (€ share), the midpoint of the range set forth on the cover of this prospectus), after deducting the estimated underwriting discounts and commissions and estimated offering expenses payable by us, our pro forma net tangible book value estimated at March 31, 2013 would have been approximately $ million (€ million), representing $ per share (€ per share). This represents an immediate increase in net tangible book value of $ per share (€ per share) to existing shareholders and an immediate dilution in net tangible book value of $ per share (€ per share) to new investors purchasing shares in this offering. Dilution for this purpose represents the difference between the price per share paid by these purchasers and net tangible book value per share immediately after the completion of the offering.

The following table illustrates this dilution to new investors purchasing shares in the offering.

Each $1.00 increase (decrease) in the offering price per share, respectively, would increase (decrease) the pro forma net tangible book value after this offering by $ per share (€ per share) and the dilution to investors in the offering by $ per share (€ per share).

The following table sets forth, on a pro forma basis as of March 31, 2013, giving effect to this offering, the total number of shares owned by existing shareholders and to be owned by new investors, the total consideration paid and the average price per share paid by our existing shareholders and to be paid by new investors purchasing shares in this offering. The calculation below is based on an assumed initial public offering price of $ per share (€ per share), the midpoint of the estimated price range set forth on the cover page of this prospectus, before deducting estimated underwriting discounts and commissions and estimated offering expenses payable by us:

Each $1.00 increase (decrease) in the offering price per share, respectively, would increase (decrease) the total consideration paid by new investors by $ million (€ million) and increase (decrease) the percentage of total consideration paid by new investors by approximately %, assuming that the number of shares offered by us, as set forth on the cover page of this prospectus, remains the same.

The table above is based on actual our ordinary shares outstanding as of March 31, 2013 and additional shares of our ordinary shares issuable upon the automatic conversion of all of our outstanding preferred shares upon the consummation of this offering pursuant to the Share Conversion. The table above does not include:

If the underwriters exercise their over-allotment option in full, the following will occur:

The summary income statement and balance sheet data for the years ended and as of December 31, 2012 and 2011 of Prosensa Holding B.V. are derived from the consolidated financial statements included in this prospectus. The summary income statement and balance sheet data for the three months ended and as of March 31, 2013 and 2012 are derived from the unaudited consolidated financial statements included in this prospectus. We maintain our books and records in euros, and we prepare our financial statements under IFRS as issued by the IASB.

This financial information should be read in conjunction with “Presentation of financial and other information,” “Management’s discussion and analysis of financial condition and results of operations” and our consolidated audited and condensed consolidated unaudited financial statements, including the notes thereto, included in this prospectus.

Our business is primarily conducted in the European Union, and we maintain our books and records in euros. We have presented results of operations in euros. On May 15, 2013, the exchange rate was €0.777 to $1.00. In this prospectus, translations from euros to U.S. dollars were made at the rate of €0.781 to $1.00, the official exchange rate quoted as of March 31, 2013 by the European Central Bank. Such U.S. dollar amounts are not necessarily indicative of the amounts of U.S. dollars that could actually have been purchased upon exchange of euros at the dates indicated. All amounts paid to us under our agreement with GSK are paid in British pounds. In this prospectus, translations from British pounds to euros (a) relating to payments made on or before March 31, 2013 were made at the rate in effect at the time of the relevant payment and (b) relating to future payments were made at a rate of £1.00 to €1.183, the official exchange rate quoted as of March 31, 2013 by the European Central Bank.

The following table presents information on the exchange rates between the euro and the U.S. dollar for the periods indicated:

Management’s discussion and analysis of financial condition and results of operations

You should read the following discussion and analysis of our financial condition and results of operations together with the information under “Selected financial information” and our consolidated audited and condensed consolidated unaudited financial statements, including the notes thereto, included in this prospectus. The following discussion is based on our financial information prepared in accordance with IFRS as issued by the IASB, which might differ in material respects from generally accepted accounting principles in other jurisdictions. The following discussion includes forward-looking statements that involve risks, uncertainties and assumptions. Our actual results may differ materially from those anticipated in these forward-looking statements as a result of many factors, including but not limited to those described under “Risk factors” and elsewhere in this prospectus.

To date, we have financed our operations through private placements of equity securities, upfront, milestone and expense reimbursement payments received from GlaxoSmithKline, or GSK, under our research and development collaboration and license agreement, or the GSK Agreement, as well as funding from patient organizations, governmental bodies and bank loans. From January 1, 2002 until March 31, 2013, we raised gross proceeds of €56.4 million from private placements of equity securities and received £41.5 million (€47.4 million) in payments from GSK and €5.5 million in loans from patient organizations and governmental bodies. As of March 31, 2013, we had cash and cash equivalents of €36.1 million. To date, we have not generated any revenues from royalties or product sales. Based on our current plans, we do not expect to generate royalty or product revenues unless and until GSK obtains marketing approval for, and commercializes, drisapersen or any of the product candidates it licenses from us or we obtain marketing approval for, and commercialize, any of our product candidates for which we have retained commercialization rights.

We have generated losses since we began our drug development operations in 2002. For the years ended December 31, 2012 and 2011, we incurred net losses of €9.9 million and €11.6 million, respectively, and for the three months ended March 31, 2013 and 2012, we incurred net losses of €3.4 million and €2.7 million, respectively. As of March 31, 2013, we had an accumulated deficit of €44.2 million. We expect to continue incurring losses as we continue our clinical and preclinical development programs, apply for marketing approval for our product candidates, and subject to obtaining regulatory approval of our product candidates, build a sales and marketing force in preparation for the potential commercialization of our product candidates.

In 2009, we entered into the GSK Agreement for the development and commercialization of RNA-based therapeutics for DMD. Under this agreement, we granted GSK an exclusive worldwide license to develop and commercialize our lead compound, drisapersen. We have also granted GSK an exclusive option to obtain an exclusive worldwide license for our next most advanced compound, PRO044. In addition, GSK has an exclusive option to obtain an exclusive worldwide license for either PRO045 or PRO053, and an exclusive option to obtain an exclusive worldwide license for either PRO052 or PRO055. PRO045 is paired with PRO053, and PRO052 is paired with PRO055, because each of the product candidates in the respective pairings addresses a patient sub-population of a similar size and is at a comparable stage of development. Including amounts already paid and potential payments related to compounds to which GSK has not yet exercised its option, we are eligible for up to £428 million (€505 million) in total milestone payments upon successful compound development and commercialization and percentage royalties in the low tens on product sales. Of the £428 million in milestone payments, £104 million (€120 million) relate to development activities including option exercise payments; £195 million (€232 million) relate to regulatory achievements, such as gaining regulatory approval; and £129 million (€153 million) relate to commercial sales activities, such as achieving threshold worldwide net sales levels. A substantial portion of the milestone payments is related to drisapersen.

We will retain the full rights to the product candidates that are not licensed by GSK, and for each product candidate licensed by GSK from each of the pairings of product candidates described above, we will retain an option, which may be exercised following certain events, to certain commercial rights in a selected European territory. All of our other DMD compounds fall outside of the scope of this agreement, and we intend to develop and commercialize them ourselves or consider partnerships. Under the agreement, we are prohibited from separately developing any compound intended to directly induce single exon skipping in the dystrophin gene for the treatment of DMD targeting the same exon that is the subject of a program under the agreement. See “Business—Collaboration, license and funding arrangements—GlaxoSmithKline.”

In 2009, we received a £16 million (€17.2 million) nonrefundable upfront payment, and in total we have received £41.5 million (€47.4 million), under the GSK Agreement. Since 2009, we have recognized €28.7 million of this revenue, and €18.7 million is currently recorded as deferred revenue and is expected to be recognized over the coming two years. All payments by GSK to us are made in British pounds.

We have entered into an exclusive worldwide license agreement with Leiden University Medical Center, or LUMC, for the rights to apply LUMC’s proprietary RNA modulation exon-skipping technology to develop treatments for DMD, other neuromuscular disorders and indications outside the field of neuromuscular disorders. We are obligated to make milestone payments upon the occurrence of events with respect to each subfield in which we pursue a drug indication using the LUMC patent rights, including commencing the first toxicity study, successfully completing the first Phase I study, filing for regulatory approval and satisfying certain sales thresholds. The aggregate milestone payments could total approximately €1.4 million, if we achieve such milestones in relation to an initial orphan drug indication. If we achieve such milestones in relation to a non-orphan drug indication, the aggregate milestone payments could

total €5.5 million. We may also be obligated to pay LUMC additional milestone payments of €1.25 million per product in relation to products approved for additional orphan drug indications. In addition, we are obligated to pay LUMC a mid-single digit percentage royalty on net sales on a country-by-country basis if and when any of our products is brought to market. If we sublicense our rights under the LUMC agreement to a third party, as we have to GSK, we are obligated to pay LUMC a tiered royalty percentage (ranging from the low-to-mid-twenties) on the net licensing income and a low single-digit percentage royalty on the net sales generated by the sublicensee. See “Business—Collaboration, license and funding arrangements—Leiden University Medical Center.”

To date, we have paid LUMC €3.6 million in milestone payments under the agreement.

Our revenues to date have consisted principally of license revenue and collaboration revenue. For 2011 and 2012 and the first quarter of 2013, all of our license revenue and collaboration revenue was generated under the GSK Agreement.

The timing of our operating cash flows may vary significantly from the recognition of the related cash flows, as the revenue from some upfront or initiation payments is deferred and recognized as revenue when earned, while other revenue is earned when received, such as milestone payments or service fees. Our revenue has varied substantially, and is expected to continue to vary, from quarter to quarter and year to year, depending upon, among other things, the structure and timing of milestone events, the number of milestones achieved, the level of revenues earned for ongoing development efforts, any new collaboration arrangements we may enter into and the terms we are able to negotiate with our partners. We therefore believe that period to period comparisons should not be relied upon as indicative of our future revenues.

We receive research grant funding from various institutions and governmental bodies.

To fund our research and development activities, we have also obtained loans from patient organizations and governmental bodies that generally bear interest at below-market interest rates. The difference between fair value and the notional amount at inception is treated as a donation received for research we performed and classified as other income.

We are obligated to make payments to LUMC upon the achievement of specified milestones, if any of our product candidates become successfully commercialized and if we generate certain revenues from sublicensing to a third party our rights under the agreement, as we have to GSK. For the three months ended March 31, 2013 and 2012 and for the years ended December 31, 2012 and 2011, we did not incur any costs associated with license revenue because we did not generate any applicable revenue.

We expect that our total research and development expense in 2013 will be in the range of €20-25 million. Our research and development expense mainly relates to the following key programs:

Since January 1, 2009, we cumulatively spent €56.1 million on research and development. Our research and development expense may vary substantially from period to period based on the timing of our research and development activities, including timing due to regulatory approvals and enrollment of patients in clinical trials. Research and development expense is expected to increase as we advance the clinical development of our DMD product candidates and to further advance the research and development of our non-DMD product candidates. The successful development of our product candidates is highly uncertain. At this time we cannot reasonably estimate the nature, timing and estimated costs of the efforts that will be necessary to complete the development of, or the period, if any, in which material net cash inflows may commence from, any of our product candidates. This is due to numerous risks and uncertainties associated with developing drugs, including the uncertainty of:

A change in the outcome of any of these variables with respect to the development of drisapersen or any other product candidate that we may develop could mean a significant change in the costs and timing associated with the development of drisapersen or such product candidate. For example, if the FDA or other regulatory authority were to require us to conduct preclinical and clinical studies beyond those which we currently anticipate will be required for the completion of clinical development or if we experience significant delays in enrollment in any clinical trials, we could be required to expend significant additional financial resources and time on the completion of the clinical development.

We expect that our general and administrative expense will increase in the future as our business expands and we incur additional costs associated with operating as a public company. These public company-related increases will likely include costs of additional personnel, additional legal fees, accounting and audit fees, directors’ and officers’ liability insurance premiums and costs related to investor relations. In addition, we may grant share-based compensation awards to key management personnel and other employees in connection with this offering.

Our cash and cash equivalents have been deposited primarily in saving and deposit accounts with original maturities of 3 months or less. Saving and deposit accounts generate a small amount of interest income. We expect to continue this investment philosophy.

License revenue remained stable at €1.4 million for each of the three month periods ended March 31, 2012 and 2013. In 2009, we received a £16 million (€17.2 million) nonrefundable upfront payment from GSK in connection with our entry into the GSK Agreement. We are recognizing this payment ratably over five years, and in the three month periods ended March 31 in each of 2013 and 2012, we recognized revenue of €0.9 million. In addition, we recognized revenue of €0.5 million related to unconditional milestone payments for the PRO045/PRO053 program and the PRO052/PRO055 program received under the GSK Agreement in the three month periods ended March 31 in each of 2012 and 2013.

Collaboration revenue increased from €0.6 million in the three month period ended March 31, 2012 to €1.0 million in the three month period ended March 31, 2013. This revenue was generated mainly from services provided under the GSK Agreement related to the research and development of drisapersen and PRO044.

Other income is incidental by nature and was insignificant in the three months ended March 31, 2012 and 2013.

Research and development expense for the three months ended March 31, 2012 and 2013

Research and development expense increased 7.4% from €3.8 million in the three months ended March 31, 2012 to € 4.1 million in the three months ended March 31, 2013. Our research and development expense is highly dependent on the development phases of our projects and therefore fluctuates highly from year to year. We expect that our total research and development costs in 2013 will be in the range of €20-25 million.

The variances in expense between the three months ended March 31, 2012 and the corresponding period in 2013 are mainly due to the following projects:

General and administrative expense increased from €1.1 million in 2012 to €1.8 million in the three months ended March 31, 2013 over the prior year period due to additional audit fees and professional advisory expense of €0.7 million related to a potential capital markets transaction. We expect that general and administrative expense will increase in the future as our business expands and we incur additional costs associated with operating as a public company.

Other gains/(losses) were insignificant in the three months ended March 31, 2012 and 2013.

Finance income decreased 9% in the three months ended March 31, 2013 compared to the three months ended March 31, 2012 due to lower interest rates.

Finance cost increased 129% from €0.1 million in the three months ended March 31, 2012 to €0.2 million in the three months ended March 31, 2013. Higher finance costs were mainly due to new borrowings from patient organizations and governmental bodies of €2.3 million in the twelve month period ended March 31, 2013.

License revenue decreased 12.0% from €6.5 million in 2011 to €5.7 million in 2012. In 2009, we received a £16 million (€17.2 million) nonrefundable upfront payment from GSK in connection with our entry into the GSK Agreement. We are recognizing this payment ratably over five years, and in each of 2012 and 2011, we recognized revenue of €3.4 million. In addition, we recognized revenue of €2.3 million and €3.1 million related to unconditional milestone payments received under the GSK Agreement in the years 2012 and 2011, respectively. With respect to the year ended December 31, 2012, the unconditional payments received under the GSK Agreement related to the clinical candidate selection of PRO052 and PRO055, as well as an advanced option payment for PRO044. With respect to the year ended December 31, 2011, the unconditional milestone payments received under the GSK Agreement related to PRO045 and PRO053.

Collaboration revenue decreased slightly from €2.2 million in 2011 to €2.1 million in 2012. This revenue was generated mainly from services provided under the GSK Agreement related to the research and development of drisapersen and PRO044.

Other income is incidental by nature. In 2012, we received a loan from a patient organization bearing an interest rate below the market interest rate. The difference between fair value and the notional amount at inception is considered a donation and recorded as other income. In 2011, we received a grant that was recorded as other income.

Research and development expense decreased 6.2% from €15.3 million in 2011 to € 14.4 million in 2012. Our research and development expense is highly dependent on the development phases of our research projects and therefore fluctuates highly from year to year. We expect that our total research and development costs in 2013 will be in the range of €20-25 million.

The variances in expense between 2011 and 2012 are mainly due to the following projects:

General and administrative expense decreased 22.7% from €5.2 million in 2011 to €4.0 million in 2012. The decrease was primarily related to legal fees related to financing activities, non-cash share-based compensation and the move to larger facilities in Leiden during 2011.

We expect that general and administrative expense will increase in the future as our business expands and we incur additional costs associated with operating as a public company.

Finance income increased 83.4% from €0.4 million in 2011 to €0.8 million in 2012. Finance income in these periods consisted primarily of interest income recognized on short-term deposits. Finance income increased in 2012 as a result of an increase in average cash and cash equivalents following our private placement of preferred equity securities to new and existing investors with total net proceeds of €22.7 million in January 2012.

Finance cost increased 66.5% from €0.2 million in 2011 to €0.3 million in 2012. Higher finance costs are mainly due to new borrowings from patient organizations and governmental bodies of €3.9 million in 2012.

To date, we have financed our operations through private placements of equity securities, upfront, milestone and expense reimbursement payments from GSK and funding from patient organizations, governmental bodies and bank loans.

Our cash and cash equivalents as of March 31, 2013 were €36.1 million. The table below summarizes our consolidated unaudited statement of cash flows for each of the three month periods ended March 31, 2012 and 2013:

The net cash used in operating activities decreased slightly from €4.6 million in the three months ended March 31, 2012 to €4.3 million in the three months ended March 31, 2013 due to higher amounts of interest received in the three month period ended March 31, 2013 in the amount of €0.1 million, changes in the working capital balances of €0.8 million in the three month period ended March 31, 2013 as compared to the three month period ended March 31, 2012, offset by higher operating loss of €0.6 million. For an explanation of the higher operating loss of €0.6 million, please see “—Results of operations”.

The net cash used in investing activities increased slightly from €0.1 million in the three month period ended March 31, 2012 to €0.2 million in the three month period ended March 31, 2013 due to higher investments in tangible fixed assets.

The decrease in net cash generated from financing activities from €11.7 million in the three month period ended March 31, 2012 to approximately nil in the three month period ended March 31, 2013 is due to minimal financing activities in the three month period ended March 31, 2013 compared to the three month period ended March 31, 2012, which included proceeds of the first half of our private placement of 9,107,144 preferred (Class B) shares to new and existing investors for total net proceeds of €22.7 million agreed to in January 2012 and €0.2 million of new borrowings.

The table below summarizes our consolidated audited statement of cash flows for the years ended December 31, 2012 and 2011:

The decrease in net cash used in operating activities by 49.9% from €7.3 million in 2011 to €3.7 million in 2012 was mainly due to a lower operating loss of €1.5 million and the receipt of milestone payments that were €6.6 million higher in 2012 compared to 2011, offset by changes in the working capital balances in 2012 as compared to 2011 in the amount of €5.1 million. For an explanation of the lower operating loss of €1.5 million, please see “—Results of operations.”

The decrease in net cash used in investing activities by 82.9% from €2.2 million in 2011 to €0.4 million in 2012 was due to our move to a larger facility in Leiden in 2011, which resulted in relatively higher investments in laboratory and office equipment in that year.

The increase in net cash generated from financing activities from €0.5 million in 2011 to €26.0 million in 2012 is mainly due to our private placements of 9,107,144 preferred (Class B) shares to new and existing investors for total net proceeds of €22.7 million in January 2012. In addition, in 2012 we received funding from patient organizations and governmental bodies totalling €3.9 million, offset by the repayment of finance leases in the amount of €0.4 million.

During the three months ended March 31, 2013 we did not obtain new financing. As such, the table below only summarizes our sources of financing for the years ended December 31, 2012 and 2011.

Our sources of financing in 2012 were private placements of equity securities providing total net proceeds of €22.7 million and funding from patient organizations and governmental bodies

totally €3.9 million, offset by the repayment of finance leases in an amount of €0.4 million. Our sources from financing in 2011 were government grants and finance leases for laboratory equipment.

As of March 31, 2013, we had long-term debt of €6.4 million, which was comprised of bank loans in the amount of €0.4 million, other loans in the amount of €5.9 million and finance lease liabilities in the amount of €0.1 million.

We have no ongoing material financial commitments, such as lines of credit or guarantees, that are expected to affect our liquidity over the next five years, other than leases.

We believe that the net proceeds of this offering, together with our existing cash and cash equivalents and anticipated milestone payments under the GSK Agreement will enable us to fund our operating expenses and capital expenditure requirements for at least the next months. We have based this estimate on assumptions that may prove to be wrong, and we could use our capital resources sooner than we currently expect.

Our present and future funding requirements will depend on many factors, including, among other things:

For more information as to the risks associated with our future funding needs, see “Risk factors.”

The following table sets forth our capital expenditures for the years ended December 31, 2012 and 2011, and for the three months ended March 31, 2013 and 2012.

During 2011, we moved to larger facilities, which resulted in additional investments in laboratory and office equipment. We plan to make investments in 2013 to enhance our research and development capacity, for example, the purchase of an automated system to stain and detect proteins. For the three month period ended March 31, 2013, we invested €0.3 million in tangible and intangible fixed assets. Our budgeted capital expenditures for the full year 2013 are approximately €0.6 million, and we anticipate that they will be funded from existing cash balances.

The table below sets forth our contractual obligations and commercial commitments as of December 31, 2012 that are expected to have an impact on liquidity and cash flow in future periods.

In 2006, we received a bank loan of €900,000 from ABN Amro N.V. that matures in 2017. The loan bears interest equal to Euribor plus 1.75% per year. We repay an amount of €25,000 per quarter, and €475,000 was outstanding under this agreement as of March 31, 2013. We also have an

undrawn revolving facility with €243,000 of availability as of March 31, 2013. The amount available to us under the credit facility decreases by €46,000 per year. The security for the loan and the credit facility consists of all cash and cash equivalents that are deposited with ABN Amro, including a minimum of €500,000 that must be maintained at all times in an ABN Amro bank account.

As of the date of this prospectus, we do not have any, and during the periods presented we did not have any, off-balance sheet arrangements.

We are exposed to a variety of financial risks: market risk (including foreign exchange risk and interest rate risk), credit risk and liquidity risk. Our overall risk management program focuses on the unpredictability of financial markets.

We are exposed to foreign exchange risk arising from various currency exposures, primarily with respect to the British pound and the U.S. dollar. Our functional currency is the euro, but we receive payments from our main business partner GSK in British pounds and acquire materials in U.S. dollars. No formal practice has been established to manage the foreign exchange risk against our functional currency. As of March 31, 2013, there was outstanding a net amount of trade receivables denominated in British pounds of €1.8 million and trade payables denominated in US dollars of €0.2 million.

Proceeds from the offering in U.S. dollars will be converted to our functional currency, the euro.

Our interest rate risk arises from long-term borrowings that are issued at variable rates. This risk is partially offset by cash held at variable rates. Borrowings issued at fixed rates expose us to interest rate risk. During 2012 and 2011, our borrowings were denominated in euros. We manage our cash flow interest rate risk by using floating-to-fixed interest rate swaps. As of December 31, 2012, if interest rates on borrowings had been 0.1% higher/lower with all other variables held constant, after-tax total comprehensive loss for the year ended December 31, 2012 would have been €6,000 lower/higher as a result of changes in the fair value of the borrowings. As of December 31, 2011, if interest rates on borrowings had been 0.1% higher/lower with all other variables held constant, after-tax total comprehensive loss for the year ended December 31, 2011 would have been €4,000 lower/higher as a result of changes in the fair value of the borrowings. The effect of a change in interest rates of 0.1% on borrowings would have had an insignificant effect on after-tax total comprehensive loss for the year as a result of changes in the fair value of the floating to fixed interest rate swap.

Over the coming years, GSK funding (milestone payments, collaboration revenue and reimbursable research expenses) remains critical for our product development programs and is considered the main credit risk. We have a limited group of external counterparties of which the most significant is GSK. We manage credit risk on a group basis.

Our cash and cash equivalents are invested primarily in saving and deposit accounts with original maturities of three months or less. Saving and deposit accounts generate a small amount of interest income. For banks and financial institutions, only independently rated parties with a minimum rating of ‘A’ are accepted at the beginning of the term.

We do business with a limited group of external parties, of which the most significant is GSK. If external parties are independently rated, these ratings are used. If there is no independent rating, the credit quality of these parties is assessed, taking into account their financial position, past experience and other factors. As of March 31, 2013 no credit limits had been exceeded since the beginning of 2011. We have not incurred any losses over the reporting period, and management does not expect losses from non-performance by counterparties (for example, GSK).

Our management’s discussion and analysis of our financial condition and results of operations is based on our financial statements, which we have prepared in accordance with IFRS as issued by the IASB. The preparation of these financial statements requires us to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements, as well as the reported revenues and expenses during the reporting periods. Actual results may differ from these estimates under different assumptions or conditions.

While our significant accounting policies are more fully described in the notes to our consolidated financial statements appearing elsewhere in this prospectus, we believe that the following accounting policies are the most critical to aid you in fully understanding and evaluating our financial condition and results of operations.

Nonrefundable upfront licensing fees and certain guaranteed, time-based payments that require continuing involvement in the form of research and development, manufacturing or other efforts are recognized in the period of expected performance. Other upfront payments are recognized by reference to the stage of completion of the underlying agreement at the balance sheet date when the rendering of services can be estimated reliably. The rendering of services can be estimated reliably when the stage of completion of the transaction at the balance sheet date can be measured reliably and costs incurred for the transaction and the costs to complete the transaction can be measured reliably. When these criteria are not met, revenue arising from the rendering of services is recognized only to the extent of the expenses recognized that are recoverable. Milestone payments are recognized when substantive services have been performed in relation to the payment and contractual milestones having been fully achieved.

Collaboration revenue, which may or may not be related to a licensing agreement, is recognized on the basis of labor hours delivered at the contractual full-time employee rates.

The related cost of license revenue is based on the determination of net license revenue as defined in our license agreements after deducting allocable expenses and is subject to a certain amount of judgment.

Research expenses are recognized as expenses when incurred. Costs incurred on development projects are recognized as intangible assets as of the date as of which it can be established that it is probable that future economic benefits attributable to the asset will flow to us considering its technological and commercial feasibility. This is generally the case when regulatory approval for commercialization is achieved and costs can be measured reliably. Given the current stage of the development of our products, no development expenditures have yet been capitalized. Intellectual property-related costs for patents are part of the expenditure for the research and development projects. Therefore, registration costs for patents are expensed when incurred as long as the research and development project concerned does not meet the criteria for capitalization.

As part of the process of preparing our financial statements we are required to estimate our accrued expenses. This process involves reviewing quotations and contracts, identifying services that have been performed on our behalf, estimating the level of service performed and the associated cost incurred for the service when we have not yet been invoiced or otherwise notified of the actual cost. The majority of our service providers invoice us monthly in arrears for services performed or when contractual milestones are met. We make estimates of our accrued expenses as of each balance sheet date in our financial statements based on facts and circumstances known to us at that time. We periodically confirm the accuracy of our estimates with the service providers and make adjustments if necessary. The significant estimates in our accrued research and development expenses are related to fees paid to clinical research organizations, or CROs, in connection with research and development activities for which we have not yet been invoiced. We base our expenses related to CROs on our estimates of the services received and efforts expended pursuant to quotes and contracts with CROs that conduct research and development on our behalf.

The financial terms of these agreements are subject to negotiation, vary from contract to contract and may result in uneven payment flows. There may be instances in which payments made to our vendors will exceed the level of services provided and result in a prepayment of the research and development expense. In accruing service fees, we estimate the time period over which services will be performed and the level of effort to be expended in each period. If the actual timing of the performance of services or the level of effort varies from our estimate, we adjust the accrual or prepayment expense accordingly. Although we do not expect our estimates to be materially different from amounts actually incurred, our understanding of the status and timing of services performed relative to the actual status and timing of services performed may vary and could result in us reporting amounts that are too high or too low in any particular period.

We have adopted share-based compensation plans pursuant to which our directors and selected employees are granted the right to acquire (non-voting) depository receipts (“Depositary

Receipts”) issued in respect of our ordinary shares. We refer to these rights as “options.” Upon the exercise of an option, ordinary shares are issued to a Dutch foundation called Stichting Administratiekantoor Prosensa Holding (the “Foundation”), whose purpose is to facilitate administration of options and pool the voting interests of the underlying shares. The Foundation thereupon grants a Depository Receipt for each issued ordinary share to the person exercising his or her option. Legal title to the shares issued under the share-based compensation plan is held by the Foundation, and the voting rights attached to the shares are exercised by the Foundation.

The vesting of options is generally conditional on the employee completing a four year period of service. Each option grant vests based on the following schedule: (a) 25% on the first anniversary of the date of the grant, provided that on that date the relevant officer or employee is still employed by us, and (b) the remaining 75% in 36 equal monthly installments over a three year period following the first anniversary of the date of grant subject to continued employment of the relevant employee. The company may decide to accelerate the vesting of the options as a result of a change of control.

On December 5, 2012, we granted options to members of our management board that vest only upon a liquidity event such as a change of control or an initial public offering and are subject to continued employment until the date such an event occurs. The number of options that vest will depend on the value of our shares in the change of control transaction or our share price following an initial public offering, as applicable.

The outstanding options granted can be exercised up to 10 years after the grant date and then expire.

The methodology we have used to date in measuring share-based compensation expense is described below. Following the completion of this offering, option pricing and values will be determined based on the quoted market price of our ordinary shares.

We value options granted to employees and directors at fair value on the date of grant and recognize the corresponding compensation expense of those grants, net of estimated forfeitures, over the requisite service period, which is generally the vesting period of the respective grant. Market performance conditions attached to option grants are included when determining the grant date fair value of such options. We issue options with only service-based vesting conditions or with service-based vesting conditions combined with vesting conditions subject to a liquidity event and record the expense for these options using the straight-line method for each separate vesting tranche.

The fair value of options under the various grants is based on a Monte-Carlo simulation using the following assumptions:

We have historically been a private company and lack company-specific historical and implied volatility information. Therefore, we estimate our expected volatility based on the historical volatility of publicly traded peer companies and expect to continue to do so until such time as we have adequate historical data regarding the volatility of our traded share price. The publicly traded peer companies we use for this analysis include companies active in the development of drugs for unmet medical needs, including DMD, and/or applying RNA-modulating or genetics-based technology and therapies and include our main competitor. Most of the selected guideline companies only have a pipeline with compounds in development and have not yet commercialized any products. Volatility is estimated based on the observed daily share price returns of publicly traded peer companies over a historic period equal to the period for which expected volatility is estimated. Volatility is defined as the annualized standard deviation of share price returns.

We expect all vested options to be exercised. Therefore we consider the expected life of the options to be in line with the vesting period of the options.

As of March 31, 2013, the outstanding options had the following exercise prices:

During 2011, the exercise price of 519,350 options was changed to €0.01 to align the exercise price of the options granted under our 2007 Employee Stock Option Plan and our 2010 Stock Option Plan. The incremental fair value granted amounted to €410,000 and was the difference between the fair value of the options with revised exercise price (€0.01) and the fair value of the options with the original exercise price, both estimated as of the date of the modification. From

the modification date this incremental fair value is recognized as an expense over the remainder of the applicable vesting period, in addition to the expense recognized for the original fair value of the options.

These assumptions represent our best estimates, but the estimates involve inherent uncertainties and the application of our judgment. As a result, if factors change and we use significantly different assumptions or estimates, our share-based compensation expense could be materially different. We recognize compensation expense for only the portion of equity instruments that are expected to vest. In developing a forfeiture rate estimate, we have considered our historical experience to estimate pre-vesting forfeitures. If our actual forfeiture rate is materially different from the estimate, our share-based compensation expense could be different from what we have recorded in the current period.

The following table summarizes by grant date the number of shares subject to options granted between January 1, 2011 and December 31, 2012:

On December 5, 2012, we granted to the members of our management board 1.0 million options that vest only upon a liquidity event such as a change of control or our initial public offering, subject to the continued employment of the members of the management board. In the event of our initial public offering, the number of options eligible to vest is automatically reduced from 1.0 million to 800,000, of which Giles Campion, Luc Dochez and Berndt Modig are each eligible to vest in up to 133,333 options and Hans Schikan is eligible to vest in up to 400,000 options. The vesting of the threshold number of 12.5% of the total number of options granted is subject to the sustained closing market price for our ordinary shares exceeding €8.90 per share during any 20 consecutive trading days outside a lock-up or blackout period. The number of options subject to vesting increases for every €1.00 increment in the sustained closing market price for our ordinary shares, with 12.5% of the total number of the options granted subject to vesting on the day immediately following a sustained closing market price of at least €8.90 per share and 100% subject to vesting on the day immediately following a sustained closing market price of at least €15.90 per share. Upon each subsequent achievement of a sustained, higher closing market price (in €1.00 increments), an additional number of options will be eligible to vest. Upon achievement of such sustained closing market price levels, 25% of the options vest on the day immediately following attainment of such pricing levels, and an additional 2.083% will vest at the end of each successive one-month period following the initial vesting date until the third anniversary of the initial vesting date. The options may not be exercised unless the grantee continues to be an employee, officer or director of, or consultant or advisor to, us as of the date of exercise. As of December 31, 2012 and March 31, 2013, the requirements to vest were deemed not probable,

and therefore no expenses have been recognized. Until the date a liquidity event is considered to be probable, no expense will be recognized for these grants.

We have made, as part of our share-based compensation plan, awards entitling recipients to acquire Depositary Receipts (“Restricted Shares”) against payment of the nominal value of the underlying ordinary shares (the “Purchase Price”), subject to our right to repurchase all or part of such Depositary Receipts at the lower of the Purchase Price and the fair value of the ordinary shares during the four year vesting period if the participant ceases to perform services to us. We have the right to repurchase 100% of the Restricted Shares awarded, and this right to repurchase shares will be reduced based on the following schedule: (a) 25% on a date of the year following the vesting commencement date no later than the anniversary of the grant, and (b) the remaining 75% in 36 equal monthly installments over a three year period following the first anniversary of the first vesting date.

The following table summarizes by grant date the number of shares subject to Restricted Shares awarded between January 1, 2011 and December 31, 2012:

The fair value of the Restricted Share awards was measured based on the estimated fair value of the ordinary shares at the moment of purchase the Depository Receipts, which was €0.70 in 2012 and €1.00 in 2011, in line with the valuations of our ordinary shares. We recognize the corresponding compensation expense of those awards, net of estimated forfeitures, similar to the approach taken for option grants as indicated above, over the requisite service period, which is generally the vesting period of the respective award. We do not plan to pay dividends in the foreseeable future; therefore, dividend payments have not been considered in the valuation of the Restricted Share awards.

The fair value of our ordinary shares is determined by our management board and supervisory board, and takes into account our most recently available valuation of ordinary shares performed by an independent valuation firm and our assessment of additional objective and subjective factors we believe are relevant and which may have changed from the date of the most recent valuation through the date of the grant.

Our management board and supervisory board consider numerous objective and subjective factors to determine their best estimate of the fair value of our ordinary shares as of each grant date, including the following:

In determining the fair values of our ordinary shares as of each award grant date, three generally accepted approaches were considered: income approach, market approach and cost approach. Based on our stage of development and information available, we have determined that the income approach is the most appropriate method, and when applicable, we have also employed the prior sale of company stock method to estimate our aggregate enterprise value. In addition, we have taken into consideration the guidance prescribed by the American Institute of Certified Public Accounts (AICPA) Audit and Accounting Practice Aid, Valuation of Privately-Held-Company Equity Securities Issued as Compensation.

Discounted cash flow (DCF), a form of the income approach, is an estimate of the present value of the future monetary benefits expected to flow to the owners of a business. It requires a projection of the cash flows that the business is expected to generate. These cash flows are converted to present value by means of discounting, using a rate of return that accounts for the time value of money and the appropriate degree of risks inherent in the business. The discount rate in the DCF analysis is based upon a weighted average cost of capital (WACC) calculated at each valuation date. The WACC is a method that market participants commonly used to price securities and is derived by using the Capital Asset Pricing Model and inputs such as the risk-free rate, beta coefficient, equity risk premiums and the size of the company.

The prior sale of company stock method considers any prior arm’s length sales of the company’s equity securities. Considerations factored into the analysis include: the type and amount of equity sold, the estimated volatility, the estimated time to liquidity, the relationship of the parties involved, the timing compared to the ordinary shares valuation date and the financial condition and structure of the company at the time of the sale.

the exercise price is based on a comparison with the total equity value rather than, as in the case of a regular call option, a comparison with a per share price. Thus, ordinary shares are considered to be a call option with a claim on the enterprise at an exercise price equal to the remaining value immediately after the preferred shares are liquidated. The OPM uses the Black Scholes option-pricing model to price the call options. This model defines the securities’ fair values as functions of the current fair value of a company and uses assumptions such as the anticipated timing of a potential liquidity event and the estimated volatility of the equity securities. In the allocation of equity, we have also considered valuation outcomes of ordinary shares through a sale of the company versus an initial public offering and considered the probabilities of each at each valuation date, since the treatment of the liquidation rights is different for these two events. The aggregate value of the ordinary shares is then divided by the number of ordinary shares outstanding to arrive at the per share value.

A valuation was performed by an independent valuation firm as of December 2010 and applied to all option grants in 2011. For the grant on March 22, 2011 and the other grants made in September through November, 2011, we relied on the December 2010 valuation report, which we deemed reasonable based on our progress at that time. Of the total 716,000 options granted in 2011, 707,500 options were granted on March 22, 2011. Between the valuation of our ordinary shares performed as of December 2010 and March 2011, there were no events in our business that were deemed to have an effect on the valuation and thus we believed the December 2010 valuation to continue to be reasonable. Furthermore, there were no significant results in 2011 from any of our development programs including the Phase III-DMD114044 pivotal trial initiated in December 2010, the continuation of the dose escalation study of PRO044 and the preclinical safety studies for PRO045 and PRO053 on-going throughout 2011. Additional valuations were performed by an independent valuation firm as of September 30, 2012 and December 5, 2012 for share-based compensation grants in 2012.

Our ordinary shares valuation as of December 2010 relied on a DCF to derive our total enterprise value. The cash flow projections were based on probability-weighted scenarios which considered estimates of time to market of our products, market share and pricing. The cash flow projections were estimated over a period equal to the expected product life cycle, and a terminal value period was not applied. All DMD indications in development were included in estimating cash flow projections, most importantly drisapersen. The expected sales were estimated based on a regional level, estimated patient populations and market shares. Production and research and development costs were estimated at the indication level with general and administrative costs and selling and marketing costs assessed at the overall company level. Cash flow projections also incorporated expected royalties and milestones related to the collaboration agreement with GSK. A WACC of 16.0% was applied. Equity was allocated using the CVM and, applied retrospectively, an OPM, resulting in a determination by the supervisory board and the management board of a value per ordinary share of €1.00. The CVM and OPM rely on the anticipated timing and probability of a liquidity event based on then current plans and estimates of our supervisory board and management board regarding a liquidity event of 80-85% probability of a sale of the company and 15-20% probability of an initial public offering. We assumed volatility of 60% based on historical trading volatility for our publicly traded peer companies and a time to liquidity of 1.5 years.

In 2011 we also concluded an amendment to the GSK agreement related to the development terms for the PRO044 program. In this amendment the timing of the milestone payment for GSK licensing PRO044, which had been anticipated in the second quarter of 2011, was restructured, and the anticipated licensing to GSK of PRO044 was deferred significantly. In January 2012, we raised total net proceeds of €22.7 million in a private placement of our preferred (Class B) shares. The additional Class B shares were issued on a pari passu basis to the original Class B shares issued in December 2008 with a liquidation preference senior to Class A, Class O and ordinary shares. The events above in the aggregate had a downward effect on our valuation of our ordinary shares as of the end of 2011 and in 2012.

Our ordinary shares valuation as of September 30, 2012 and December 5, 2012 relied on a DCF as well as the prior sale of company stock method in connection with the January 2012 financing round to derive our total enterprise value. Management has determined that there were no events intervening between the respective valuation dates and therefore the analysis and inputs remained the same, except for adjustments within the analysis for the passage of time. The cash flow projections were based on probability-weighted scenarios which considered estimates of time to market of our products, market share and pricing. Projections were updated from the December 2010 valuation for anticipated timing of placebo-controlled clinical trial results, our progress since the last valuation date and the development of a competing drug for DMD that increased the risk of our losing a first-mover advantage. A WACC of 15.5% was applied. Under the prior sale of company stock method, we used the implied value from the latest financing round in January 2012 and an estimated annualized return on equity over the period between the financing round and the valuation date for the valuation of the enterprise value as of September 30, 2012 considering the factors noted above. Equity was allocated using the CVM and OPM, resulting in a value per ordinary share of €0.70. The CVM and OPM rely on the anticipated timing and probability of a liquidity event based on then current plans and estimates of our supervisory board and management board regarding a liquidity event of 80-85% probability of a sale of the company and 15-20% probability of an initial public offering. We assumed volatility of 60% based on historical trading volatility for our publicly traded peer companies and a time to liquidity of 0.50 years.

A discount for lack of marketability (DLOM) of 15% and 10%, as of December 2010 and September 30, 2012, respectively, was applied to reflect the increased risk arising from the inability to readily sell the shares. When applying the DLOM, the Black-Scholes option model was used. Under this method, the cost of the put option, which can hedge the price change before the privately held shares can be sold, was considered as the basis to determine the DLOM. The cost of the put option was the only factor considered and applied in the discount. The put option analysis reflects the potential loss from marketability over the expected time to liquidity and is a commonly applied approach to estimate this discount.

On , we and our underwriters determined the estimated price range for this offering, as set forth on the cover page of this prospectus. The midpoint of the price range is $ per share. In comparison, our estimate of the fair value of our ordinary shares was €0.70 ($ ) per share as of September 30, 2012 and December 5, 2012. In addition, the price per share in our January 2012 financing round was € ($ ) per share. We note that, as is typical in initial public offerings, the estimated price range for this offering was not derived using a formal determination of fair value, but was determined by negotiation between us and the underwriters. Among the factors

that were considered in setting this range were our prospects and the history of and prospects for our industry, the general condition of the securities markets and the recent market prices of, and the demand for, publicly traded shares of generally comparable companies. Specifically, we believe that the difference between the fair value of our ordinary shares as of September 30, 2012 and December 5, 2012 and the midpoint of the estimated price range for this offering is primarily due to the results of the first placebo-controlled clinical study of drisapersen in April 2013 and the conversion of our preferred shares into ordinary shares.

We are subject to income taxes in the Netherlands. Significant judgment is required in determining the use of net operating loss carry forwards and taxation of upfront and milestone payments for income tax purposes. There are many transactions and calculations for which the ultimate tax determination is uncertain. Where the final tax outcome of these matters is different from the amounts that were initially recorded, such differences will impact the current and deferred income tax assets and liabilities in the period in which such determination is made.

No tax charge or income was recognized during the reporting periods since we are in a loss-making position and have a history of losses. We have tax loss carry-forwards of €45.5 million and €42.1 million as of March 31, 2013 and December 31, 2012, respectively. As a result of the Dutch income tax law, tax loss carry-forwards are subject to a time limitation of nine years. Deferred income tax assets are recognized for tax losses and other temporary differences to the extent that the realization of the related tax benefit through future taxable profits is probable. We recognize deferred tax assets arising from unused tax losses or tax credits only to the extent the relevant fiscal unity has sufficient taxable temporary differences or if there is convincing other evidence that sufficient taxable profit will be available against which the unused tax losses or unused tax credits can be utilized by the fiscal unity. Our judgment is that sufficient convincing other evidence is not available and a deferred tax asset is therefore not recognized.

In order to promote innovative technology development activities and investments in new technologies, a corporate income tax incentive has been introduced in Dutch tax law called the Innovation Box. For the qualifying profits, we effectively owe only 5% income tax, instead of the general tax rate of 25.5% which results in an estimated effective tax rate of 10%. The agreement with the tax authorities is currently signed for the years 2011 to 2015 but is expected to be extended.

From January 1, 2002 through March 31, 2013, we received the following loans from patient organizations and governmental bodies: €3,140,000 from Association Française contre les Myopathies (AFM), €640,000 from Agentschap NL, €500,000 from the Stichting Duchenne Parents Project, €387,000 from Charley’s Fund, €300,000 from Everest International Pte Ltd, €250,000 from Cure Duchenne, €163,000 from Aktion Benni & Co. and €65,000 from Villa Joep. These arrangements are generally in the form of below-market interest rate loans that become due upon the meeting of certain milestones in product development, generally a minimum threshold of commercialization success or successful completion of certain clinical trials. Significant judgment is required in determining when these pre-determined milestones are met and may vary over time, implying a change in the value of the loans. The AFM agreement gives us the option to terminate the agreement if we undergo a change of control. If we exercise our option to terminate the agreement, we are required to repay the loan, together with interest. In the

event that we abandon the program for reasons not justified by a scientific or medical reason, we are similarly required to repay the loan, together with interest. The AFM agreement also requires us to grant to AFM a non-exclusive royalty-free license to the intellectual property covered by the agreement in the event that we abandon the research funded by the agreement. We also have received a number of other loans from patient organizations and governmental bodies in smaller amounts.

There are no IFRS standards as issued by the IASB or interpretations issued by the IFRS interpretations committee (e.g. IFRS 10, 11, 12, 13 and IAS 19R) that are effective for the first time for the financial year beginning on or after January 1, 2013 that would be expected to have a material impact on our financial position.

On April 5, 2012, the JOBS Act was signed into law. The JOBS Act contains provisions that, among other things, reduce certain reporting requirements for an “emerging growth company.” As an emerging growth company, we are electing to take advantage of the following exemptions:

The JOBS Act permits an “emerging growth company” such as us to take advantage of an extended transition period to comply with new or revised accounting standards applicable to public companies. We are choosing to “opt out” of this provision and, as a result, we will comply with new or revised accounting standards as required when they are adopted. This decision to opt out of the extended transition period under the JOBS Act is irrevocable.

These exemptions will apply for a period of five years following the completion of our initial public offering or until we no longer meet the requirements of being an “emerging growth company,” whichever is earlier. We would cease to be an emerging growth company if we have more than $1.0 billion in annual revenue, have more than $700 million in market value of our ordinary shares held by non-affiliates or issue more than $1.0 billion of non-convertible debt over a three-year period.

Drisapersen, which is also referred to as PRO051 or GSK2402968, is being developed in collaboration with GlaxoSmithKline, or GSK. Drisapersen aims to restore dystrophin expression and improve muscle condition and function in the largest known sub-population of DMD patients. In clinical trials, drisapersen has been shown to produce dystrophin expression and have a beneficial therapeutic effect on DMD patients. A Phase II placebo-controlled study of drisapersen in 53 DMD patients was completed and demonstrated a statistically significant and clinically important difference in the primary endpoint, which was the distance walked in the six minute walk test, or 6MWD, between the placebo group and the continuous active-treatment group at a dose of 6 mg/kg/week after 24 weeks. This clinically meaningful benefit was maintained after 48 weeks of treatment, and drisapersen was well tolerated throughout the duration of this study.

PRO044, our next most advanced product candidate, addresses a separate sub-population of DMD patients. We developed PRO044 using our exon-skipping technology to generate a product

candidate with the same mechanism of action that is used by drisapersen. PRO044 is currently in a Phase I/II study in Europe, which we expect to complete in mid-2013. We have four additional earlier-stage compounds that address other distinct sub-populations of DMD patients. Of these, PRO045 entered clinical trials in the first quarter of 2013, and we anticipate that PRO053 will enter clinical trials in mid-2013. PRO052 and PRO055 are in advanced preclinical development. We have also started a research program, PROSPECT, which includes a new and innovative application of our exon-skipping technology platform to specifically target rarer mutations in the dystrophin gene.

In addition, GSK has the option to exclusively license either PRO045 or PRO053 and the further option to exclusively license either PRO052 or PRO055. PRO045 is paired with PRO053, and PRO052 is paired with PRO055, because each product candidate in the respective pairings addresses a similar-sized patient sub-population and is at a comparable stage of development. We will retain the full rights to the product candidates that are not licensed by GSK, and for each product candidate licensed by GSK from each of the pairings of product candidates described above, we will retain the option to certain commercial rights in a selected European territory. All of our other DMD compounds fall outside of the scope of this agreement, and we intend to develop and commercialize them ourselves or consider partnerships.

We started operations in 2002 and are located in Leiden, the Netherlands. We work closely with Leiden University Medical Center, or LUMC, with whom we entered into an exclusive licensing agreement in 2003 for LUMC’s proprietary RNA modulation exon-skipping technology to develop treatments for DMD, other neuromuscular disorders and indications outside the field of neuromuscular disorders. Since 2002, we have raised €56.4 million from private placements of equity securities, including to a number of venture capital firms. In addition, we have received grants and loans from several DMD-focused patient advocacy organizations to support our research of therapies for DMD. As of March 31, 2013 we had €36.1 million in cash and cash equivalents.

The following table summarizes our product development pipeline in DMD as well as DM1 and HD:

We and GSK have jointly undertaken the largest ever patient trials conducted globally for a DMD product candidate. The strength of our collaboration underscores our ability to work successfully with a major pharmaceutical company, and we benefit from access to GSK’s scientific expertise, global infrastructure and regulatory relationships to advance the development of drisapersen. In partnership with GSK, we aim to achieve the first approval in all major markets for a disease-modifying therapy for DMD and bring to market a product to address the substantial unmet medical need for this currently fatal condition.

Given similarities in technology and targets, we expect there to be substantial development and commercial synergies between drisapersen and our product candidates, PRO044, PRO045, PRO053, PRO052 and PRO055, which each address distinct sub-populations of DMD patients. We are leveraging the know-how from clinical development and regulatory advice for drisapersen to optimize strategies, reduce development risk and accelerate speed to market for these products, thereby expanding our commercial DMD portfolio and maximizing the patient population addressed by our product candidates.

In the longer term, we believe that the depth of our internal scientific capabilities and strength of our clinical pipeline and relationships with patient advocacy groups put us in a strong position to commercialize our own products. Since we are developing DMD products for different but closely related patient sub-populations, we believe that the additional infrastructure required to commercialize our proprietary DMD products will be relatively limited. We therefore believe that it would be cost-effective for us to establish our own marketing effort and sales force.

We intend to leverage our proprietary technology platform and expertise in RNA modulation to further progress our technology for exon skipping and to develop other product candidates for rare genetic diseases such as myotonic dystrophy and Huntington’s disease.

As of March 31, 2013, we owned or exclusively licensed 6 U.S. patents and 16 U.S. patent applications and 3 European patents and 23 European patent applications covering our RNA modulation technology platform and our exon-skipping product candidates. We plan to continue to leverage this portfolio to create value and to file new patent applications, in-license other intellectual property and take other steps to expand and strengthen our intellectual property position.

We may also enter into strategic collaborations that deliver additional expertise and enhance implementation of our strategy.

Human genes contain the DNA blueprint instructions for protein synthesis and gene regulation in the body. Within the DNA strand, multiple series of three-letter nucleotide bases (known as “codons”) together make up the active instructions called “exons,” which are read by cellular machinery to make proteins. Interspersed among exons are sections of DNA known as “introns,” which have no direct role in protein synthesis.

To make a particular protein, the relevant section of DNA is copied (in a process known as transcription) to make pre-mRNA (pre-messenger ribonucleic acid), which contains both exons and introns and therefore cannot be read by the cellular machinery as an instruction to make a protein. The introns are then removed (in a process known as splicing) so that the instructions in the active mRNA (messenger RNA) can be read by the cellular machinery to make a particular protein.

The dystrophin gene, which is central to the pathology of DMD, is comprised of 79 exons, which are interspersed with non-coding introns. In patients with DMD, synthesis of the dystrophin protein is disrupted because of mutations in the DNA that contains the dystrophin gene. The extent and nature of the mutations are different in different sub-populations of DMD patients and may be due to, among other things, deleted or duplicated exons or small mutations that result in disrupted coding of the mRNA. This defective mRNA is said to be “out of the transcription reading frame” and results in a premature halt of the protein synthesis and a truncated, non-functional dystrophin. Consequently, patients with DMD have a lack of functional dystrophin protein in their muscles. Our aim is to restore the coding reading frame of mRNA so that it can be read to produce functional dystrophin protein.

Our technology enables us to design sequences of nucleotide bases that bind to specified regions of pre-mRNA involved in the splicing of exons. As a result, when the pre-mRNA is spliced to mRNA, the disrupted coding section is skipped or passed over completely, and the transcription reading frame is corrected. The single stranded oligonucleotides (short nucleotide sequences) that we

design are known as antisense oligonucleotides, or AONs; and our preferred chemical structure is a backbone of 2’ O-methyl phosphorothioate (or 2’O-Me) groups that protect the AONs from rapid enzyme degradation once they are inside the body’s cells. In DMD, we apply this technology to address particular mutations occurring at different sites in the dystrophin gene.

Our RNA modulation platform technology can also be applied to treat genetic disorders that are caused by mutations where trinucleotide bases, such as CAG or CUG, are expanded in certain genes, generating a longer series of trinucleotide repeats than is normal. These extended repeated sequences can cause the resulting RNA transcript or protein to be unstable, dysfunctional or even toxic, and lead to various diseases. We have AON programs targeting two such disorders, HD and DM1.

DMD is a rare, severe muscle wasting disease that occurs in up to 1 in 3,500 male births. It is commonly diagnosed between the ages of three to five, when boys begin to show signs of impaired motor development. Boys with DMD continue to develop in strength and function, albeit at a lower rate than healthy boys, up until about 7 years. They then begin to lose muscle function, generally becoming wheelchair-bound around the age of 12, with loss of respiratory and cardiac function in the ensuing years. DMD patients typically die in their twenties of either cardiac or respiratory failure.

Currently, there is no approved disease-modifying treatment for DMD. Corticosteroid therapy is the current standard of care in most developed countries and may be administered as early as 3 years, although administration commonly starts at 4-6 years. Steroids have been demonstrated to temporarily preserve muscle function and delay disease progression milestones, such as time to wheelchair dependency, by approximately 2 years, but the ultimate course of the disease is unaffected. In addition, steroids have potentially serious side effects, negatively affecting growth, bone mineral density and the immune system.

DMD is caused by various mutations in the dystrophin gene, such as deletions, duplications or small mutations of one or more exons, which result in a lack of functional dystrophin in the muscle fiber. Dystrophin is a protein with a central role in linking the contractile apparatus of a muscle fiber to the cell membrane and surrounding extracellular matrix. An absence or a low level of dystrophin also leads to reduced levels of various other proteins. This leads to progressive muscle fiber degeneration characteristic of DMD, with fatty and fibrous tissue replacement of muscle.

Deletions of any number of exons in the dystrophin gene may occur. The different mutations result in distinct sub-populations of DMD patients. The figure below shows the effect of the deletion of exons 48—50 in the dystrophin gene.

In this example, the deletion of exons 48—50 results in an mRNA that is out of the transcription reading frame since exons 47 and 51 do not fit together. Consequently, functional dystrophin will not be produced.

Our therapeutic strategy for DMD is to use AON-induced exon skipping to allow a shorter but still functional dystrophin protein to be produced so that muscle performance in patients with DMD may be maintained or even improved. Our AONs bind highly specifically to a selected exon in the pre-mRNA coded by the dystrophin gene. The exon is selected because it is, for instance, adjacent to a region where one or more exons have been deleted. As a result, the exon to which the AON binds is skipped over in the splicing process, allowing two non-consecutive exons to be joined across the gap. This results in what is termed “restoration of the transcription reading frame”—in other words, the genetic instructions or code become legible again, and a shorter but still functional dystrophin protein is produced. The figure below shows how an AON binding with exon 51 of the gene’s pre-mRNA can result in an in-frame mRNA transcript and production of a shorter but still functional dystrophin protein.

In this example, there is a deletion of exons 48 to 50; drisapersen binds with exon 51 in the pre-mRNA, and after splicing this results in exon 47 and exon 52 becoming consecutive exons in the mRNA. Since exon 47 and exon 52 connect properly, an in-frame mRNA results and a shorter but still functional dystrophin protein will be produced, which is expected to result in improved muscle physiology and hence clinical outcome.

Natural history data can illustrate expected rates of physical decline, which helps to put into context the effects of novel drug treatments. The six minute walk test (6MWT) is a test that measures the distance a subject can walk in 6 minutes using a standardized corridor length and turning point at each end (the six minute walk distance or 6MWD). This test has been used in observational research studies to follow the natural history of DMD disease progression over time as subjects gradually lose the ability to walk.

Several key studies have demonstrated the effect of DMD on 6MWD. One study reported an average 57 meter decrease at 52 weeks from baseline in average 6MWD by boys with DMD, whereas comparable healthy boys showed an average increase in 6MWD of 13 meters. A more recent study of 113 boys reported an average decrease in 6MWD of 23 meters in the first year of observation and 65 meters in the second year. In the latter study, when grouped by age, boys below 7 years remained stable with a slight increase in average 6MWD in the first and second years, but the average 6MWD of boys over 7 declined by about 42 meters and 80 meters, respectively.

The diagram below is a conceptual representation created by analyzing patient data from various studies to contrast 6MWD performance by DMD patients and healthy control subjects and to illustrate the typical decline in 6MWD performance by boys with DMD over age 7.

The 6MWT is accepted by U.S. and European regulators to be an appropriate primary outcome measure for DMD trials. It is believed that the test is a sensitive measure to show effects of treatment within a timeframe of one year. Other measures of treatment effectiveness include the North Star Ambulatory Assessment, or NSAA, which has been validated in DMD at various ages, and timed tests such as rise from the floor, stair climbing and 10 meter walk/run. Muscle strength in upper and lower limbs (knees, elbows and shoulders) is also assessed, as is breathing function.

The 6MWD has successfully been used as a primary endpoint to assess ambulatory function in studies leading to regulatory approval of therapies designed to treat the underlying cause of disorders with neuromuscular and pulmonary manifestations that are associated with deterioration in 6MWD over time, such as Pompe’s disease, mucopolysaccharidosis I, Hunter syndrome and pulmonary arterial hypertension. Individual results for 6MWD compare each subject’s baseline result against a result at a study time point, and individual and averaged differences in 6MWD from baseline are further compared between treatment and non-treatment groups. The data comparing treatment and non-treatment groups may be presented in a number of ways, such as absolute differences (meters) and percent change from baseline. There is not yet an agreed regulatory position on the clinical relevance of absolute differences in meters or percent change from baseline in DMD, however studies of therapies for the diseases mentioned above have reported differences from baseline between placebo and treatment groups of 28 to 44 meters, representing an improvement of 8 - 13%, which has been considered clinically meaningful in these contexts and used in support of applications for regulatory approval. We and GSK supplement the 6MWD primary endpoint with secondary outcome functional measures, imaging and biomarkers to demonstrate the multidimensional response to therapy, which we believe is likely to be important for applications for regulatory approval.

Some of the mutations that we are targeting for treatment are very rare, and numbers of eligible patients for clinical trials are in the low double digits. In these sub-populations, it is not feasible to design clinical studies involving statistically meaningful numbers of placebo-controlled patients. For this reason, together with our partner GSK, we have started a natural history study

for which we intend to recruit up to 250 DMD patients from the ages of 3-18 at clinics in ten countries. The goal of this study is to characterize DMD at various stages of progression using the same measures used in the clinical studies, such as 6MWD, and use the data to help interpret clinical trial results for our product candidates that are targeted at ultra-rare mutations that cause DMD, for which we anticipate that it will be difficult to recruit placebo groups.

Our lead compound, drisapersen, is an AON with highly specific binding to exon 51 of the dystrophin gene’s pre-mRNA. The binding of drisapersen to exon 51 specifically induces exon 51 to be skipped when the mRNA for the dystrophin protein is created from the pre-mRNA. Given the frequencies reported in various international DMD mutation databases, the skipping of exon 51 could in principle correct the transcription reading frame and produce shortened but functional dystrophin expression in approximately 13% of all DMD patients.

Drisapersen was granted orphan drug status in the United States and the European Union in 2009. In the United States, if a product with orphan status receives FDA approval, the FDA will not approve a later product for the same indication that uses the same active ingredient for seven years, unless the later product is shown to be clinically superior. In the European Union, the EMA will not approve a later product for the same indication and with the same method of action for ten years after the earlier product receives EMA approval, subject to certain exceptions, including the demonstration of clinical superiority.

We demonstrated clinical proof of concept in four DMD patients receiving a single intramuscular 0.8 mg dose of drisapersen in a trial initiated in May 2006. In this study, drisapersen was safe and effective in specifically inducing exon 51 skipping and restoring dystrophin expression to 35% of normal levels in up to 94% of muscle fibers in the treated muscle area.

We conducted a subsequent Phase I/II dose-ranging safety study in which drisapersen was administered to 12 patients subcutaneously, once weekly for 5 weeks. The study, initiated in March 2008 and conducted at two European clinical centers, demonstrated that drisapersen was well-tolerated in all patients and novel dystrophin expression was detected in each treated patient. An open-label extension study of this Phase I/II study was initiated in August 2009 and is ongoing.

In October 2009, we entered into a worldwide collaboration agreement with GSK for the further clinical development of drisapersen. GSK licensed exclusive worldwide rights to develop and commercialize drisapersen. Under the agreement for drisapersen, all development, commercialization and regulatory work in support of drisapersen falls under the sole budgetary and decision-making responsibility of GSK. We have received development milestone payments for drisapersen pursuant to the agreement, and GSK must pay us development and regulatory milestone payments, as well as royalties upon successful commercialization of drisapersen. See “—Collaboration, license and funding arrangements—GlaxoSmithKline.”

The following table sets forth information regarding completed and ongoing clinical trials of drisapersen:

Phase I/II—PRO051-02. A Phase I/II study was initiated in March 2008 to evaluate systemic administration of drisapersen. Twelve patients were given weekly subcutaneous injections for five weeks at two European clinical centers at four dosing cohorts (0.5, 2.0, 4.0 and 6.0 mg/kg). The primary endpoint was safety, and secondary endpoints included pharmacokinetics and molecular and clinical effects. Muscle biopsies were taken, and changes in RNA splicing and dystrophin protein levels assessed, at baseline and two weeks after the last dose in the 0.5 mg/kg cohort and at two and seven weeks in the other three cohorts. Novel dose-dependent dystrophin expression was detected in each patient, and specific exon 51 skipping was confirmed in the majority.

An open-label extension phase followed the initial five-week study after an interval of six to fifteen months. Improvement in 6MWD versus baseline was observed at the 12-week point in the extension phase. The extension phase is ongoing with all patients participating, although two boys were not able to complete the 6MWT at the start of the extension study (one because he had lost his ability to walk (non-ambulant) before the extension phase started, and one because he sustained a fracture and could not perform the test). At the 141-week time-point, 8 of the 10 subjects able to complete the 6MWT at the extension baseline were still able to perform the walking evaluation. Although the number of patients is small, the results appear to show delay of disease progression in these eight patients. This is particularly meaningful because the subjects’ ages ranged from 8-14 at 141 weeks, which is when their 6MWD would otherwise be expected to decline significantly based on past natural history studies. The extension study is continuing, and all subjects have now reached or exceeded the 189-week time-point. The chart below shows the 6MWD versus extension baseline for the ten subjects who were able to perform the 6MWT at the extension baseline at several points in time up to 141 weeks, which is the latest assessment date for which data are available.

Drisapersen Phase I/II—PRO051-02 extension phase 6MWD (0 = extension baseline)

Drisapersen has been generally well tolerated throughout the Phase I/II study and open-label extension phase. Transient proteinuria (protein in the urine) was observed in all twelve patients, and eleven patients demonstrated signs of proteinuria at week 12 of the extension phase. After 72 weeks, all patients were assigned to an intermittent dosing regimen (eight weeks on, four weeks off). Protein in the urine returned to normal levels in all patients during the off dosing period indicating that this effect is reversible. Other reported adverse events from this study included injection site reactions, which were seen to varying degrees of severity in all subjects, raised cystatin C (a protein indicative of kidney function), decreased C3 (a protein indicating immunological activity), low platelet counts and raised liver enzymes, including GLDH and gamma GT, which may indicate abnormal liver function. The majority of these adverse effects were transient in nature, or were resolved during the four week off-treatment period.

Phase I—DMD114118. GSK initiated this double-blind, escalating dose, randomized, placebo-controlled study in non-ambulant DMD subjects in July 2010, to assess the safety, tolerability and pharmacokinetics of single subcutaneous injections of drisapersen. It was planned that 32 non-ambulant DMD subjects would receive a single dose of 3, 6, 9, or 12 mg/kg. Twenty subjects received treatment, and the study completed after cohort 3 (9 mg/kg), because the maximum tolerated dose was identified, in line with the objectives of the study. Conclusions from the study were that the pharmacokinetics of drisapersen was similar for non-ambulant DMD subjects compared to ambulant DMD subjects for single doses. Single doses of drisapersen at 3 mg/kg and 6 mg/kg had no significant safety or tolerability concerns in the exposed subjects. Pharmacokinetics and safety results of this study together with data from the Phase I/II—PRO051-02 study suggested that drisapersen 6 mg/kg is the appropriate dose for further characterization in multiple dose studies in the non-ambulant DMD population.

Phase II—DMD114117. GSK initiated this exploratory placebo-controlled study of drisapersen at a 6 mg/kg (subcutaneous) dose in September 2010. The study consisted of three arms: (1) a continuous dosing regimen of 6 mg/kg/week, including 18 subjects; (2) an intermittent dosing regimen of 9 doses of 6 mg/kg spread over 6 weeks, followed by 4 weeks off drug, including 17 subjects; and (3) a matched placebo arm, including 18 subjects. A total of 53 DMD subjects aged 5 and above with a rise from floor of less than 7 seconds were recruited. The primary endpoint was 24-week efficacy. Secondary endpoints included safety and tolerability over 48 weeks and efficacy (including 6MWD, NSAA timed tests and muscle strength) after 48 weeks. Muscle biopsies were taken pre- and post-treatment (after 24 weeks). Although this was an exploratory study, and not statistically powered to evaluate efficacy, GSK has however reported that drisapersen demonstrated a statistically significant difference in 6MWD between the 6 mg/kg week continuous dosing arm and the placebo arm at 24 weeks. The mean difference in 6MWD was 35.09 meters (p=0.014), which is seen as a clinically meaningful benefit. P-value is a measure of how likely data is to have occurred by chance. The clinically meaningful benefit was maintained after 48 weeks of treatment, with a mean difference in 6MWD of 35.84 meters (p=0.051). Intermittent dosing did not result in a statistically significant difference from the placebo group at 24 weeks; however, GSK reported a clinically meaningful difference at 48 weeks, with a mean difference in 6MWD of 27.08 meters (p=0.147). The NSAA and timed tests showed trends that supported the 6MWD findings. Little change in muscle strength was observed at either time point for either treatment arm. Dystrophin data analysis is ongoing. Drisapersen was generally well tolerated. Injection site reactions and renal events (including proteinuria) were more frequent in the drisapersen treatment arms. There were no reports of thrombocytopenia and no subject discontinued treatment.

Phase II—DMD114876. This is an ongoing GSK-initiated study in the United States comparing two doses of drisapersen (3 mg/kg/week and 6 mg/kg/week) in 51 subjects over 48 weeks. The study began in November 2011, and the primary outcome measure is 6MWD at 24 weeks. Secondary outcome measures include the NSAA, timed tests and muscle strength tests. In addition, muscle biopsies are collected and analyzed for dystrophin production and muscle imaging is being investigated as an exploratory outcome measure in collaboration with the National Institutes of Health. The population is similar to the subjects enrolled in the Phase II study described above. After this time point, all boys are withdrawn from therapy to assess the pharmacokinetics and clinical effect of removal of treatment. An extension study is available after 48 weeks. Enrollment was completed in November 2012, and results are currently expected to be available in the first quarter of 2014.

Phase III—DMD114044. GSK initiated this ongoing pivotal randomized, double-blind, placebo-controlled study in December 2010. The study assesses once-weekly subcutaneous administration of drisapersen at 6 mg/kg dosing in 186 boys over five years of age and with a minimum 6MWD of 75 meters at enrollment. The goal of the study is to demonstrate a mean improvement of 30 meters in 6MWD at 48 weeks compared with placebo. Secondary outcome measures include the NSAA, timed tests, muscle strength tests and quality of life measures. Muscle biopsies are analyzed for dystrophin production. Enrollment is complete. Results are currently expected to be made public in the fourth quarter of 2013.

Phase II/III continuation—DMD114349. GSK initiated this open-label continuation study for up to 220 subjects completing the DMD114117 and DMD114044 clinical studies. Subjects receive doses of 6mg/kg week, and the study has been ongoing since in September 2011 with over 180 subjects enrolled to date. There has been a number of significant adverse event reports associated with this study, relating to thrombocytopenia (a decrease in the number of platelets that help blood to clot) and proteinuria (protein in the urine).

Clinical trial experience to date with drisapersen indicates adverse events which include proteinuria, local injection site reactions (pain, bruising, erythema, induration, pigmentation), thrombocytopenia, and increases in certain liver enzymes. In addition to the adverse events noted above, single reports have been received of the following clinical conditions: intracranial venous sinus thrombosis (considered unrelated by the sponsor), extramembranous glomerulonephritis and nephrotic-linked proteinuria.

Our second exon skipping product candidate for DMD is PRO044, which, like drisapersen, is a highly sequence-specific AON that, in this case, induces exon 44 to be skipped when the mRNA for the dystrophin protein is created from the pre-mRNA. Given the frequencies reported in various international DMD mutation databases, the skipping of exon 44 could in principle correct the transcription reading frame and produce shortened but functional dystrophin expression in approximately 6% of all DMD patients. PRO044 has obtained orphan drug designation in the United States and the European Union.

We initiated an ongoing dose-escalation trial, assessing six doses (0.5, 1.5, 5, 8, 10 and 12 mg/kg/week) in 18 DMD patients in December 2009. Subjects received PRO044 subcutaneously at 0.5, 1.5, 5, 8, 10 or 12 mg/kg/week (3 subjects per dose). Additionally, nine of the 18 subjects received an additional five administrations intravenously at 1.5, 5 or 12 mg/kg/week. Key endpoints include dystrophin expression, safety and tolerability and pharmacokinetic assessments. Enrollment was completed in the first quarter of 2013. Follow-on program design and timing will be confirmed pending the technical review of these and other emerging data. PRO044 is currently on clinical hold in the United States pending the results of long-term preclinical safety studies; it is anticipated that these will be completed in the fourth quarter of 2013.

Under the terms of our collaboration and license agreement with GSK, GSK has an option to an exclusive worldwide license to develop and commercialize PRO044. See “—Collaboration, license and funding arrangements—GlaxoSmithKline.”

PRO045 has a similar chemical structure and the same mechanism of action as drisapersen and PRO044 and induces exon 45 skipping when the mRNA for the dystrophin protein is created from the pre-mRNA. Given the frequencies reported in various international DMD mutation databases, the skipping of exon 45 could in principle correct the transcription reading frame and produce shortened but functional dystrophin expression in approximately 8% of all DMD patients. PRO045 has been granted orphan drug designation in the United States and the European Union, and we commenced a Phase I/II study of PRO045 in the first quarter of 2013 in Europe. PRO053 induces exon 53 skipping and could in principle correct the transcription reading frame and produce functional dystrophin expression in approximately 8% of all DMD patients. PRO053 has been granted orphan drug designation in the United States and the European Union. We expect to commence a Phase I/II study for PRO053 in mid-2013.

PRO052 and PRO055 induce exon 52 skipping and exon 55 skipping, respectively. Both have been granted orphan drug designation in the United States and the European Union and are currently in advanced preclinical development. Finally, our PROSPECT program specifically targets the rare mutations in the first part of the dystrophin gene. This program is still in the discovery phase and is built on a new and innovative application of our exon-skipping technology platform.

DMD is a rare disease, and our DMD product candidates target discrete sub-populations of DMD patients that are distinguished by different mutations in the dystrophin gene. After drisapersen, our subsequent product candidates target mutations of decreasing prevalence or increasing rarity, affecting such small populations of patients that they are sometimes referred to as “ultra-orphan.” With increased rarity of mutations and affected patients, it is not feasible to conduct fully powered pivotal studies. Regulatory authorities acknowledge that placebo study arms are less robust and scientifically meaningful as patient population size decreases. For this reason, we are working closely with the FDA, EMA and several national competent authorities in Europe on the design of alternative pathways to approval for our therapeutic candidates. Our proposed extrapolation principle is that if exon skipping works for one AON compound that is shown to be safe and effective, then the principle should to a certain extent also apply to subsequent compounds for rarer sub-populations. We believe our natural history study will enable such alternative approval pathways by facilitating direct comparison of natural history data and

interventional study data without needing to recruit large placebo groups for every exon skipping product candidate.

Myotonic dystrophy type 1 (DM1) is the most common neuromuscular dystrophy, affecting 1 in 8,000 individuals worldwide. DM1 is characterized by progressive, multi-system symptoms that typically include muscle weakness and wasting, myotonia (temporary rigidity or slow relaxation of muscles), cardiac conduction defects/arrhythmia and hormonal changes. Life expectancy is reduced due to increased mortality resulting from pulmonary and cardiac complications. The disease affects males and females equally, and the severity of symptoms increases in successive family generations. There is currently no disease modifying treatment for DM1. DM1 is caused by expansion of an unstable (CUG) trinucleotide repeat in the non-coding region of the DMPK gene. This leads to DMPK mRNA transcripts bearing long sequences of CUG nucleotide repeats that can form hairpin-like structures that bind proteins involved in RNA splicing. As a result, the splicing of certain downstream pre-mRNA transcripts that code for other proteins is affected and the resulting proteins are less or non-functional.

Our AON program for DM1, PRO135, selectively targets the toxic RNA transcripts resulting from expansion of (CUG) trinucleotide repeats in the transcription of the DMPK gene. PRO135 candidates reduce the levels of toxic transcripts in myoblasts (precursors of muscle fibers) derived from various DM1 patients. The PRO135 lead candidates are currently being tested in preclinical mouse models of DM1. Preliminary results have shown DMPK mRNA reduction in muscle as well as correction of processing of several RNA transcripts that are normally affected by the repeat expansion. Preclinical studies to identify reversal of myotonic phenotype are currently ongoing, and progression into Phase I trials is planned for early 2017. We have exclusive worldwide rights to the PRO135 program, and we are fully responsible for its research and development.

Huntington’s disease (HD) is a devastating progressive neurodegenerative disorder characterized by chorea (abnormal involuntary movement) spreading to all muscles, progressive dementia and psychiatric manifestations such as depression and psychosis. In western countries, prevalence is estimated to be 5-10 in 100,000 individuals. HD symptoms usually begin to manifest between the ages of 30 to 50; death commonly follows 15 to 20 years after onset of neurological impairment. No effective disease modifying treatment for HD currently exists. HD is caused by expansion of an unstable (CAG) trinucleotide repeat in the coding region of the HTT gene, giving rise to an expanded stretch of CAG nucleotides that become repeatedly expanded on transcription. During protein synthesis, these CAG repeats are translated into a series of uninterrupted glutamine residues, which alter the function of the HD protein and cause it to accumulate in brain cells, leading to the symptoms of HD. AON candidates in our PRO289 program target these repeats and have been shown to reduce levels of expanded HTT transcripts and mutant huntingtin protein in fibroblast cultures (precursors of connective tissue cells) derived from HD patients. We are currently testing PRO289 candidates in various preclinical models of HD. We have exclusive worldwide rights to PRO289, and we are fully responsible for its research and development.

Our technology platform enables us to modulate gene expression through the binding of specifically designed AONs to target RNA, which may induce exon skipping or exon inclusion,

reduce mutated toxic RNA or protein, remove specific protein domains or block RNA expression. We focus on genetic disorders representing market opportunities with significant unmet medical needs. Our current focus is on the design, selection and preclinical development of molecules with favorable bioactivity, safety and biodistribution profiles for use in DMD (exon skipping), DM1 (reduction of mutated toxic RNA) and HD (reduction of mutated toxic protein). However, our platform may be applied to other genetic diseases for which RNA modulation would be corrective, or to other trinucleotide repeat expansion diseases, such as several types of spinocerebellar ataxia (SCA), amyotrophic lateral sclerosis (ALS) or X-linked spinal and bulbar muscular atrophy (SBMA).

In October 2009, we entered into a research and development collaboration and license agreement with GSK to develop and commercialize RNA-based therapeutics for the treatment of DMD. The agreement was amended in July 2011. The financial terms of the agreement include an upfront payment of £16 million (€17.2 million), up to £428 million (€505 million) in total milestone payments upon successful compound development and commercialization (including amounts already paid and potential payments related to compounds to which GSK has not yet exercised its option) and percentage royalties in the low tens on product sales. Of the £428 million in milestone payments, £104 million (€120 million) relate to development activities including option exercise payments; £195 million (€231 million) relate to regulatory achievements, such as gaining regulatory approval; and £129 million (€153 million) relate to commercial sales activities, such as achieving threshold worldwide net sales levels. A substantial portion of the milestone payments are related to drisapersen.

Pursuant to the agreement, we granted GSK an exclusive worldwide license in relation to our lead compound, drisapersen. We have also granted GSK an exclusive option to obtain an exclusive worldwide license for our next most advanced compound, PRO044. In July 2011, we jointly amended the agreement to extend the period of GSK’s option to PRO044 and to revise the development plan for PRO044 in exchange for additional pre-option funding of the PRO044 program by GSK.

In addition, GSK has an exclusive option to obtain an exclusive worldwide license for either PRO045 or PRO053, and an exclusive option to obtain an exclusive worldwide license for either PRO052 or PRO055. We will retain the full rights to such of these product candidates that are not licensed by GSK, and for each of these compounds that is licensed to GSK, we will retain an option, which may be exercised following certain events, to certain commercial rights in a selected European territory.

The exclusive, worldwide patent rights and know-how for our lead compound, drisapersen, are exclusively licensed to GSK to further research, develop and commercialize this compound with the goal of commercial launch. We continue to contribute to certain development activities in support of the clinical studies under the GSK development plan, at GSK’s cost and expense.

Under the exclusive license granted to GSK, GSK has sole decision-making authority and is responsible for all research, development, regulatory, manufacturing, marketing, advertising, promotional, launch and sales and all commercial activities in connection with drisapersen.

We may receive further milestone payments for drisapersen in connection with marketing authorization filings and reimbursements achieved in major markets, and certain commercial sales achievements. We also may receive tiered patent/market exclusivity royalties from GSK in the low tens.

We have granted GSK an exclusive option to obtain an exclusive, worldwide license to the patent rights and know-how for PRO044. To date, GSK has not exercised this option. To secure the option, GSK has paid us initiation and advanced option payments, and in return we have initiated and are currently conducting research and development for PRO044. In July 2011, we jointly amended the agreement to extend the period of time in which GSK may exercise its exclusive option to PRO044 and revised the development plan for PRO044 in exchange for additional pre-option funding of the PRO044 program by GSK. When the compound meets the necessary criteria for us to produce a milestone report, GSK, upon receipt of such report, will have a limited period of time to determine whether or not to exercise its option.

Upon exercising its option, GSK will obtain the sole decision-making authority in relation to, and bear all further costs for, the continuation of the development of the PRO044 program. Upon exercise, GSK will be obligated to pay us an option exercise fee; and subsequently GSK will be obligated to pay us development and regulatory milestone payments upon successful achievement of such milestones, as well as tiered patent/market exclusivity and in some cases know-how royalties on the same conditions as described above in relation to drisapersen. In return, GSK will obtain an exclusive, worldwide license to the patent rights and know-how pertaining to PRO044 to research, develop, make, use and sell PRO044.

GSK has exclusive options to obtain an exclusive, worldwide license to the patent rights and know-how pertaining to two additional compounds: one of either PRO045 or PRO053 and one of either PRO052 or PRO055. PRO045 is paired with PRO053, and PRO052 is paired with PRO055, because each of the product candidates in the respective pairings addresses a patient sub-population of a similar size and is at a comparable stage of development. To date, GSK has not exercised these options. To secure the options, GSK has paid us non-refundable initiation and candidate selection payments, and in return we have initiated and are currently conducting development of PRO045, PRO053, PRO052 and PRO055 at our own cost. When a compound meets the necessary criteria for us to produce a milestone report, GSK, upon receipt of such milestone report, will have a limited period of time to determine whether or not to exercise its option.

Until GSK exercises its exclusive option to a compound’s specific development program, we have the responsibility for the conduct of research and development of each program in accordance with the agreed-upon development plan and must bear all related costs and expenses. Upon exercising its option, GSK will obtain the sole decision-making authority in relation to, and bear all further costs for, the continuation of the development of the program. Upon exercise, GSK will be obligated to pay us an option exercise payment; and subsequently GSK will be obligated to pay us development and regulatory milestone payments upon successfully achieving such milestones, as well as patent/market exclusivity royalties and know-how royalties on the same conditions as described above in relation to drisapersen.

Under the terms of the agreement, GSK has an exclusive option to obtain an exclusive, worldwide license to the first compound for which we produce a milestone report for the agreed-upon proof of concept study for either PRO045 or PRO053 and a further option to obtain an exclusive, worldwide license to the first compound of PRO052 or PRO055 for which we produce a milestone report for the agreed-upon proof of concept study. If GSK exercises any such option, in exchange for a reduction in milestone payments for the relevant compound, we will have an option, which may be exercised following certain events, to certain commercial rights in a selected European territory for the compound subject to GSK’s option. We will retain the full rights for any product candidates for which GSK does not exercise its option or otherwise receive a license. Under the agreement, we are prohibited from separately developing any compound intended to directly induce single exon skipping in the dystrophin gene for the treatment of DMD targeting the same exon that is the subject of a program under the agreement.

The agreement will expire on a product-by-product and country-by-country basis on the date of the expiration of all payment obligations with respect to each product in each country of commercialization. The length of such payment obligations depends on the length of patent validity for each product or in some cases a specified date after the first commercial sale of a product. The entire agreement expires upon the expiration of all payment obligations due under the agreement. The agreement may also terminate on a program-by-program basis when no compound or product is being researched, developed or commercialized by either party pursuant to the programs that are subject to the agreement. Upon expiration on a product-by-product and country-by-country basis, GSK will have an exclusive, fully-paid and royalty-free right and license to continue to commercialize the products for which it has obtained an exclusive license.

Either party may terminate the agreement, either on a program-by-program basis or in its entirety, for cause in the event of a breach or default by the other party in the performance of any of its material obligations with respect to a particular program or the agreement as a whole, if such default or breach has continued for 90 days after written notice was provided. If the parties reasonably and in good faith disagree as to whether there has been a material breach, the party that seeks to dispute the breach may contest the allegation. In the case of such a dispute, each party will attempt to reach a resolution in good faith, and if no resolution is achieved, the matter may be referred to arbitration for final settlement.

In addition, either party may terminate the agreement upon the occurrence of certain bankruptcy- or insolvency-related events.

GSK has the right to unilaterally terminate the agreement either in part or in its entirety, for any reason or no reason at all, upon 180 days prior written notice. In the event of GSK’s unilateral termination, all licenses granted to GSK with respect to the compounds and products in the terminated program (or, in the case of termination of the entire agreement, all compounds and products) will terminate, and we will have the exclusive right to research, develop and commercialize all such products. If the terminated program concerns PRO045, PRO053, PRO052 or PRO055, we shall pay to GSK a low single-digit royalty on all products we sell that contain such compound until GSK has recovered all payments made to us directly related to the product or compound and GSK’s actual costs for development thereof. In addition, all unexercised options with respect to the terminated programs will be cancelled.

In September 2003, we obtained an exclusive worldwide license from LUMC for the application of its proprietary RNA modulation exon-skipping technology to develop treatments for selected neuromuscular disorders. This technology was developed at the Human Genetics department of Professor Dr. Gert-Jan van Ommen. The license agreement gives us the rights to apply the RNA modulation technology for the development of treatments for neuromuscular disorders as well as, after an amendment of the agreement in March 2008, indications outside the field of neuromuscular disorders. We now use this intellectual property related to RNA modulation technology for all of the compounds that we are currently developing. LUMC reserves the right to use its technology for research and educational purposes and any other purpose not subject to its agreement with us. We have also granted LUMC a non-exclusive, royalty-free license to certain intellectual property we own for the purpose of enabling LUMC to perform internal, non-commercial research.

In consideration for the expansion of the licensed field to include all applications pursuant to the 2008 amendment and for the occurrence of certain milestones and events, we paid LUMC €890,000. We are also obliged to make milestone payments upon the occurrence of events with respect to each subfield in which we pursue a drug indication using the LUMC patent rights, including commencing the first toxicity study, successfully completing the first Phase I study, filing for regulatory approval and satisfying certain sales thresholds. The aggregate milestone payments could total approximately €1.4 million, if we achieve such milestones in relation to an initial orphan drug indication. If we achieve such milestones in relation to a non-orphan drug indication, the aggregate milestone payments could total €5.5 million. We also may be obligated to pay LUMC additional milestone payments of €1.25 million per product in relation to products approved for additional orphan drug indications. In addition, we are obligated to pay LUMC a mid-single digit percentage royalty on net sales on a country-by-country basis if and when any of our products is brought to market. If we sublicense our rights under the LUMC agreement to a third party, as we have to GSK, we are obligated to pay LUMC a tiered royalty percentage (ranging from the low-to-mid-twenties) on the net licensing income and a low single-digit percentage royalty on the net sales generated by the sublicensees. To date we have paid LUMC €3.6 million in milestone payments under the agreement.

If we and LUMC file for a joint patent, such patent will remain jointly owned by us and LUMC. We control any enforcement rights in case of infringement related to any of the joint patent rights and we are required to pay all patent prosecution and maintenance costs during the term of the agreement. If the agreement is terminated, we are jointly responsible with LUMC for patent prosecution and maintenance costs for any patents jointly owned by LUMC and us.

The agreement will expire on a country-by-country basis upon the latest of (a) the expiration date of the last to expire of LUMC’s patent rights issued in such country, (b) the expiration date of the last to expire grant of orphan drug status issued in such country or (c) 15 years from the first commercial sale of a product in such country. The agreement may be terminated by LUMC for (i) our failure to perform any of our material duties under the agreement that is not cured within six months’ written notice, (ii) our material breach of the agreement that is not cured within 90 days’ written notice thereof, or (iii) our insolvency. We may terminate the agreement without cause upon six months written notice.

In addition to our agreement with GSK, we have obtained the following funding from patient organizations and governmental bodies: €3,140,000 from Association Française contre les Myopathies, or AFM, €640,000 from Agentschap NL, €500,000 from the Stichting Duchenne Parents Project, €387,000 from Charley’s Fund, €300,000 from Everest International Pte Ltd, €250,000 from Cure Duchenne, €163,000 from Aktion Benni & Co. and €65,000 from Villa Joep. These arrangements are generally in the form of below-market interest rate loans that become due upon the meeting of certain milestones in product development, generally a minimum threshold of commercialization success or successful completion of certain clinical trials. The AFM agreement gives us the option to terminate the agreement if we undergo a change of control. If we exercise our option to terminate the agreement, we are required to repay the loan, together with interest. In the event that we abandon the program for reasons not justified by a scientific or medical reason, we are similarly required to repay the loan, together with interest. The AFM agreement also requires us to grant AFM a non-exclusive royalty-free license to the intellectual property covered by the agreement in the event that we abandon the research funded by the agreement. Furthermore, we have received a number of other loans from patient organizations and governmental bodies in smaller amounts. We have also received grant funding. Such grants are typically for research, and typically the grant program lasts 3 to 4 years.

We are engaged in segments of the biopharmaceutical and pharmaceutical industries that are highly competitive and rapidly changing. Large pharmaceutical, specialty pharmaceutical and biotechnology companies, academic institutions, governmental agencies and other public and private research organizations are commercializing or pursuing the development of products that target genetic disorders, including the same diseases we are targeting. If approved, we expect our product candidates to face intense and increasing competition as new products enter the DMD markets and advanced technologies become available. Our product candidates will face competition based on their safety and effectiveness, the timing and scope of regulatory approvals, the availability and cost of supply, marketing and sales capabilities, reimbursement coverage, price, patent position and other factors. Our competitors may succeed in developing competing products before we do, obtaining regulatory approval for products or gaining acceptance for the same markets that we are targeting. If we or our collaborators are not “first to market” with one of our product candidates for a given disease indication or a given product profile, our competitive position could be compromised because it may be more difficult for us to obtain marketing approval for that product candidate and/or successfully market that product candidate as a second product to market.

We believe that our key competitor in DMD is Sarepta Therapeutics, Inc., or Sarepta, a U.S. company focused on the development of their lead product candidate eteplirsen. Eteplirsen is currently in Phase II trials in DMD with eight patients in active treatment and employs the same exon 51 skipping approach as drisapersen. Sarepta may be in discussions with the FDA for accelerated approval of eteplirsen, which if granted, could place us at a competitive disadvantage. Even without accelerated approval, depending on the overall clinical profile, efficacy and commercialization of eteplirsen, Sarepta may render our development and discovery efforts in the area of DMD uncompetitive. If, however, drisapersen obtains marketing approval from the EMA prior to eteplirsen, drisapersen could have the benefit of orphan drug marketing exclusivity in Europe for ten years because both products use the same method of action (exon

skipping) for patients with DMD. Eteplirsen (or any other DMD product that uses exon skipping) would have to demonstrate a clinically relevant advantage over drisapersen (in efficacy, safety and/or pharmacokinetics) in order to defeat such market exclusivity in Europe. Because orphan drug marketing exclusivity in the United States is tied to the active ingredient rather than method of action, and drisapersen and eteplirsen use different active ingredients, if FDA marketing approval is obtained, we believe both products could be marketed simultaneously in the United States.

Other companies are also developing alternative therapeutic approaches to the treatment of DMD. For example, PTC Therapeutics, Inc. is developing ataluren, currently in Phase III development, a small molecule that enables formation of functional dystrophin in approximately 13% of DMD patients that have point mutations that create premature termination of RNA transcription and cannot be treated by exon skipping. In addition, Asklepios Biopharmaceuticals, Inc. is developing biostrophin, a gene-therapy approach currently in Phase I development. Summit plc is developing a utrophin (dystrophin-like protein) modulation program that uses orally administered small molecules to increase the production of utrophin. Summit’s most advanced molecule, SMT C1100, is currently in Phase I clinical trials.

Different therapeutic approaches aiming at muscle tissue growth through myostatin inhibition are currently being investigated in clinical studies. These include PF-06252616 by Pfizer Inc. and ACE-031 by Acceleron Pharma (in collaboration with Shire). A Phase I clinical trial to test PF-06252616, a myostatin antibody, is currently ongoing in healthy volunteers. A Phase II, dose-escalation study of ACE-031 in boys with DMD has been terminated based on preliminary safety data. Acceleron and Shire intend to resume studies of ACE-031 as soon as possible pending further analysis of safety data and following discussions with regulatory agencies. There has been no investigation of potential complementarity of exon skipping with alternative approaches such as these. In theory exon skipping and, for example, utrophin upregulation could be mutually enhancing; however experts hypothesize that there could be an issue of competition for binding at the cell membranes of the muscle cells.

In addition, corticosteroids are the current standard of care for DMD patients, although they do not address the underlying cause of DMD and have serious side effects. We believe that corticosteroids will continue to be prescribed in conjunction with any of our product candidates that obtain regulatory approval.

We develop and manufacture the drug product for our initial preclinical studies using standardized manufacturing processes in our own laboratories. A selected number of Contract Manufacturing Organizations (CMOs) manufacture scaled-up quantities of the drug, based on our advice and know-how. We and the CMOs use multiple qualified suppliers for the raw materials, and the raw materials are widely commercially available from catalog.

We expect to continue our reliance on third-party CMOs to manufacture drug supplies for clinical trials and commercial quantities of our products and drug candidates. Our policy is to contract with multiple suppliers of raw materials, drug substances, drug product formulation and filling; the exception is that the packaging and distribution of product for clinical trials is allocated to a single contractor. To avoid capacity issues, for each specific AON there is only one CMO for drug substance and one CMO for drug product, although the manufacturing process for our product

candidates is highly standardized across all CMOs. By maintaining agreements with multiple parties for the same stage of the manufacturing process, we believe we limit the risk of interruption of production and delays in clinical development and trials. If any CMOs should become unavailable to us for any reason, we believe that with the standardization of the manufacturing platform, there will be a number of potential replacement CMOs. Nevertheless, we may incur some delay in activating an alternative CMO for a new compound. In the future, we may decide to perform some parts of the drug substance production, drug product formulation, filling and packaging in-house.

We actively seek to protect the intellectual property and proprietary technology that we believe is important to our business, including by seeking and maintaining patents intended to cover our product candidates, product platform, proprietary processes and any other inventions that are commercially important to the development of our business. We also rely on trade secrets that may be important to the development of our business and actively seek to protect the confidentiality of such trade secrets.

Our success will depend on our ability to obtain and maintain patent and other proprietary protection for commercially important technology, inventions and know-how related to our business, defend and enforce our patents, preserve the confidentiality of our trade secrets and operate without infringing the valid and enforceable patents and proprietary rights of third parties. For more information, please see “Risk factors—Risks related to our intellectual property and information technology.”

As of March 31, 2013, we owned or exclusively licensed 4 U.S. patents, 11 U.S. patent applications, 1 European patent, 18 European patent applications (including 2 that are allowable), 1 international patent application, and 65 national patent applications or granted patents in other jurisdictions relating to our DMD program. As of such date we also owned or exclusively licensed 2 U.S. patents, 5 U.S. patent applications (including 1 that is allowable), 2 European patents, 5 European patent applications, 1 international application and 30 national patent applications or granted patents in other jurisdictions relating to our other discovery programs.

Included among the patent and patent applications described above are four families of patents and patent applications that we have exclusively licensed from LUMC. These patents and patent applications claim, among other things, compositions of matter, methods of production and methods of use related to our exon skipping technology. We further own or co-own 14 additional families of patents and patent applications encompassing other aspects of the same technology, for the treatment of DMD as well as distinct technologies for the treatment of other diseases for which we are developing drug candidates. Each patent family consists of patents and patent applications in the United States, as well as broadly equivalent patents in several other jurisdictions, including members of the European Patent Convention, Canada and Australia.

Our patents and patent applications directed to drisapersen include one U.S. patent and two U.S. patent applications and one European patent and one European Patent application. The issued U.S. patent expires in 2023, and the U.S. patent applications, if issued, would expire between 2021 and 2023. The European issued patent expires in 2021, and the European patent application, if issued, would also expire in 2021. Such patents and patent applications include claims to compositions of matter and second medical use. For each of our other DMD candidate compounds, we are seeking to obtain patents that include claims to compositions of matter and

second medical use. Our other issued patents and patent applications, if issued, that are directed to our DMD and other discovery programs are scheduled to expire between 2021 and 2033.

The term of individual patents depends upon the legal term of the patents in the countries in which they are obtained. In most countries in which we file, the patent term is 20 years from the earliest date of filing a non-provisional patent application. In the United States, a patent’s term may be shortened if a patent is terminally disclaimed over another patent or as a result of delays in patent prosecution by the patentee, and a patent’s term maybe lengthened by patent term adjustment, which compensates a patentee for administrative delays by the U.S. Patent and Trademark Office in granting a patent. The patent term of a European patent is 20 years from its filing date, which, unlike in the U.S., is not subject to adjustment.

The term of a patent that covers an FDA-approved drug or biologic may also be eligible for patent term extension, which permits patent term restoration as compensation for the patent term lost during the FDA regulatory review process. The Drug Price Competition and Patent Term Restoration Act of 1984, or the Hatch-Waxman Act, permits a patent term extension of up to five years beyond the expiration of the patent. The length of the patent term extension is related to the length of time the drug or biologic is under regulatory review. Patent extension cannot extend the remaining term of a patent beyond a total of 14 years from the date of product approval and only one patent applicable to an approved drug may be extended. Similar provisions are available in Europe and other jurisdictions to extend the term of a patent that covers an approved drug. In the future, if and when our products receive FDA approval, we expect to apply for patent term extensions on patents covering those products. We anticipate that some of our issued patents may be eligible for patent term extensions. See “—Government Regulation—United States—Hatch-Waxman Act.”

In August 2008, EP 1619249 (‘249) was granted to LUMC. This patent relates to exon skipping using an oligonucleotide with a certain length, directed to the interior of a broad range of exons (including exons 43 through 46 and 50 through 53), as well as a number of method claims comprising the use of such an oligonucleotide.

In 2009, AVI Biopharma, Inc. (now Sarepta) filed an opposition against EP ‘249 with the European Patent Office, or EPO, requesting revocation of the patent as granted, alleging, inter alia, lack of novelty, inventive step and sufficiency of disclosure. We on behalf of LUMC in turn requested maintenance of the patent on the basis as granted.

The EPO Opposition Division, presiding in oral proceedings on November 16, 2011, in Munich, Germany, maintained the EP ‘249 patent in an amended form. The allowed patent as maintained protects, among other things, the skipping of exon 51 in the dystrophin gene using a 14- to 40-mer AON as a potential therapy to treat DMD. We believe that the patent as maintained in amended form by the EPO Opposition Division still provides protection for our lead product candidate drisapersen. We and Sarepta both have the right to appeal the written decision of the EPO until June 15, 2013. We intend to appeal the written decision of the EPO.

Given our current stage of product development, we currently do not have a commercialization infrastructure. We have partnered our lead candidate drisapersen with GSK, and if drisapersen

receives regulatory approvals, GSK will have the right to market drisapersen in the jurisdictions where it obtains marketing approvals. We have retained a participatory role in the commercialization of drisapersen and will play an active role in the potential commercial launch thereof. Based on available population data and birth rates, a reported incidence of one in 3,500 male births and an expected average life span of 25 years, we estimate that the number of DMD patients in selected developed countries with a sustainable reimbursement infrastructure is approximately 75,000, of which about 15,000 are in the United States and 20,000 are in Europe. We believe that drisapersen could potentially address approximately 13% of DMD patients.

If the product candidates to which we have retained commercialization rights are granted marketing approval, we intend to market them with our own commercial team. We are operating in the rare disease area in which patients typically form local, national and global patient groups that are well-informed concerning the latest treatment possibilities. A relatively small number of medical centers of expertise tends to offer specialized treatment for these diseases. As a result, physicians can be located and targeted efficiently by a small and highly educated in-house team. We currently intend to focus our initial commercial efforts for the product candidates to which we have retained commercialization rights in the U.S. and European markets, which we believe represent the largest market opportunities for us. In addition, we believe that Japan and Latin America represent significant opportunities. The product candidates to which we have retained commercialization rights address smaller sub-populations than drisapersen, with each of PRO045 and PRO053 potentially addressing approximately 8% of the DMD patient population, and PRO055 and PRO052 applicable to approximately 2-4%. If GSK exercises its option to license PRO045, or alternatively PRO053, depending on which product candidate reaches the option criteria earlier, we have the option to exclusively commercialize that product candidate in a selected European territory upon regulatory approval. For the other product candidate of either PRO045 or PRO053 not licensed by GSK, we will retain global commercialization rights. The same principle applies to PRO052 and PRO055, where GSK has an option on one product candidate with the same option for us to commercialize the product candidate in a selected European territory. We will retain global commercial rights to the other product candidate.

Our business is subject to extensive government regulation. Regulation by governmental authorities in the United States, the European Union and other jurisdictions is a significant factor in the development, manufacture and marketing of any drugs and in ongoing research and development activities. All of our products are subject to rigorous preclinical and clinical trials and other pre-marketing approval requirements by the FDA, the EMA and other regulatory authorities in the United States, the European Union and in other jurisdictions.

In the United States, the FDA regulates drugs and medical devices under the Federal Food, Drug, and Cosmetic Act, or the FDCA, and regulations implemented by the agency. If we fail to comply with the applicable United States requirements at any time during the product development process, including non-clinical testing, clinical testing, the approval process or after approval, we may become subject to administrative or judicial sanctions. These sanctions could include, but are not limited to, the FDA’s refusal to allow us to proceed with clinical testing, refusal to approve

pending applications, license suspension or revocation, withdrawal of an approval, warning letters, adverse publicity, product recalls, product seizures, total or partial suspension of production or distribution, injunctions, fines, civil penalties or criminal prosecution. Any agency enforcement action could have a material adverse effect on us.

The process required by the FDA before a drug may be marketed in the United States generally involves satisfactorily completing each of the following:

The testing, collection and submission of data and the preparation of necessary applications are expensive and time-consuming. The FDA may not act quickly or favorably in reviewing these applications, and we may encounter significant difficulties or costs in our efforts to obtain FDA approvals that could delay or preclude us from marketing our products.

Preclinical tests include laboratory evaluations of product chemistry, formulation and stability, as well as studies to evaluate toxicity in animal studies, in order to assess the potential safety and efficacy of the product. The conduct of the preclinical tests and formulation of the compounds for testing must comply with federal regulations and requirements. The results of the preclinical tests, together with manufacturing information and analytical data, are submitted to the FDA as part of an Investigational New Drug, or IND, application. The IND becomes effective 30 days after receipt by the FDA, unless the FDA, raises concerns or questions about the conduct of the proposed clinical trial, including concerns that human research subjects will be exposed to unreasonable health risks. In that case, the IND sponsor and the FDA must resolve any outstanding FDA concerns before the clinical trials can begin. Submission of the IND may result in the FDA not allowing the trials to commence or not allowing the trial to commence on the terms originally specified in the IND. If the FDA raises concerns or questions either during this initial 30

day period, or at any time during the IND process, they may choose to impose a partial or complete clinical hold. This order issued by the FDA would delay either a proposed clinical study or cause suspension of an ongoing study, until all outstanding concerns have been adequately addressed and the FDA have notified the company that investigations may proceed. This could cause significant delays or difficulties in completing planned clinical studies in a timely manner.

Clinical trials involve the administration of the investigational product to human subjects under the supervision of qualified investigators. Clinical trials are conducted under protocols detailing, among other things, the objectives of the study, the parameters to be used in monitoring safety and the effectiveness criteria to be evaluated. Each protocol must be submitted to the FDA as part of the IND. An independent Institutional Review Board, or IRB, must also review and approve the clinical trial before it can begin and monitor the study until it is completed. The IRB will consider, among other things, clinical trial design, patient informed consent, ethical factors, the safety of human subjects and the possible liability of the institution. The FDA, the IRB or the sponsor may suspend or discontinue a clinical trial at any time or impose sanctions for various reasons, including a finding that the clinical trial is not being conducted in accordance with FDA requirements or the subjects are being exposed to an unacceptable health risk. Clinical testing also must satisfy extensive Good Clinical Practice rules and the requirements for informed consent.

Clinical trials typically are conducted in three sequential phases, but the phases may overlap or be combined. Additional studies may be required after approval.

Phase I clinical trials are initially conducted in a limited population to test the product candidate for safety, dose tolerance, absorption, metabolism, distribution and excretion in healthy humans or, on occasion, in patients, such as cancer patients.

Phase II clinical trials are generally conducted in a limited patient population to identify possible adverse effects and safety risks, determine the efficacy of the product candidate for specific targeted indications and determine dose tolerance and optimal dosage. Multiple Phase II clinical trials may be conducted by the sponsor to obtain information prior to beginning larger and more costly Phase III clinical trial.

Phase III clinical trials proceed if the Phase II clinical trials demonstrate that a dose range of the product candidate is effective and has an acceptable safety profile. Phase III clinical trials are undertaken in large patient populations to further evaluate dosage, provide substantial evidence of clinical efficacy and further test for safety in an expanded and diverse patient population at multiple, geographically dispersed clinical trial sites. A well-controlled, statistically relevant Phase III trial may be designed to deliver the data that the regulatory authorities will use to decide whether or not to approve a drug: such Phase III studies are referred to as ‘pivotal’.

In some cases, the FDA may approve an NDA for a product candidate with the sponsor’s agreement to conduct additional clinical trials to further assess the drug’s safety and effectiveness after NDA approval. Such post-approval trials are typically referred to as Phase IV clinical trials. These studies are used to gain additional experience from the treatment of patients in the intended therapeutic indication and to document a clinical benefit in the case of drugs approved under accelerated approval regulations. If the FDA approves a product while a

company has ongoing clinical trials that were not necessary for approval, a company may be able to use the data from these clinical trials to meet all or part of any Phase IV clinical trial requirement. Failure to promptly conduct Phase IV clinical trials could result in withdrawal of approval for products.

The results of product candidate development, preclinical testing and clinical trials are submitted to the FDA as part of an NDA. The NDA also must contain extensive manufacturing information and detailed information on the composition of the product and proposed labeling as well as payment of a user fee. Once the submission has been accepted for filing, the FDA begins an in-depth review of the NDA. Under the goals and policies agreed to by the FDA under the Prescription Drug User Fee Act, or the PDUFA, the FDA has ten months in which to complete its initial review of a standard NDA and respond to the applicant, and six months for a priority NDA. The FDA does not always meet its PDUFA goal dates for standard and priority NDAs. The review process is often significantly extended by FDA requests for additional information or clarification. The review process and the PDUFA goal date may be extended by three months if the FDA requests, or the NDA sponsor otherwise provides additional information or clarification regarding information already provided in the submission within the last three months before the PDUFA goal date.

At the conclusion of the FDA’s review they will issue an action letter. If the FDA’s evaluations of the NDA and the clinical and manufacturing procedures and facilities are favorable and there are no outstanding issues, the FDA will issue an approval letter. If the application is not approved, the FDA will issue a complete response letter, which will contain the conditions that must be met in order to secure final approval of the NDA, and when possible will outline recommended actions the sponsor might take to obtain approval of the application. Sponsors that receive a complete response letter may submit to the FDA information that represents a complete response to the issues identified by the FDA. Such resubmissions are classified under PDUFA as either Class 1 or Class 2. The classification of a resubmission is based on the information submitted by an applicant in response to an action letter. Under the goals and policies agreed to by the FDA under PDUFA, the FDA has two months to review a Class 1 resubmission and six months to review a Class 2 resubmission. The FDA will not approve an application until issues identified in the complete response letter have been addressed.

The FDA may also refer the NDA to an advisory committee for review, evaluation and recommendation as to whether the application should be approved. The FDA is not bound by the recommendation of the advisory committee, but it generally follows such recommendations. The FDA may deny approval of an NDA if the applicable regulatory criteria are not satisfied, or it may require additional clinical data or an additional pivotal Phase III clinical trial. Even if such data are submitted, the FDA may ultimately decide that the NDA does not satisfy the criteria for approval. Data from clinical trials are not always conclusive and the FDA may interpret data differently than we or our collaborators do. Once issued, the FDA may withdraw a drug approval if ongoing regulatory requirements are not met or if safety problems occur after the drug reaches the market. In addition, the FDA may require further testing, including Phase IV clinical trials, and surveillance programs to monitor the effect of approved drugs which have been commercialized. The FDA has the power to prevent or limit further marketing of a drug based on the results of these post-marketing programs. Drugs may be marketed only for the approved indications and in accordance with the provisions of the approved label. Further, if there are any modifications to a

drug, including changes in indications, labeling or manufacturing processes or facilities, we may be required to submit and obtain FDA approval of a new NDA or NDA supplement, which may require us to develop additional data or conduct additional preclinical studies and clinical trials. We cannot be sure that any additional approval for new indications for any product will be approved on a timely basis, if at all.

The FDA has several programs that are intended to facilitate and expedite development and review of new drugs to address unmet medical need in the treatment of serious or life-threatening conditions. These programs are intended to help ensure that therapies for serous conditions are available as soon as it can be concluded that the therapies benefits justify their risks. These programs include breakthrough therapy designation, fast track designation, priority review and accelerated approval.

Breakthrough therapy designation is intended to expedite the development and review of products for serious and life-threatening conditions. Preliminary clinical evidence must demonstrate the drug may have substantial improvement over other available therapy. This designation conveys all of the same features of fast track designation, as well as more intensive FDA guidance throughout the development program. This guidance can include meetings throughout the development cycle, providing timely advice to ensure both the nonclinical and clinical programs are as efficient as practicable, and includes involvement of senior managers and experienced staff in cross-disciplinary and collaborative reviews. In general, sponsors must apply for breakthrough therapy designation, although the FDA may suggest to the sponsor that they consider submitting a request for the designation.

The FDA’s fast track program is intended to facilitate the development and expedite the review of drugs that are intended for the treatment of a serious or life-threatening condition for which there is no effective treatment and which demonstrate the potential to address unmet medical needs for the condition. Under the fast track program, the sponsor of a new product candidate may request the FDA to designate the product candidate for a specific indication as a fast track drug concurrent with or after the filing of the IND for the product candidate. The FDA must determine if the product candidate qualifies for fast track designation within 60 days of receipt of the sponsor’s request.

If fast track designation is obtained, the FDA may initiate review of sections of an NDA before the application is complete. This rolling review is available if the applicant provides, and the FDA approves, a schedule for the submission of the remaining information and the applicant pays applicable user fees. However, the time period specified in the PDUFA, which governs the time period goals the FDA has committed to reviewing an application, does not begin until the complete application is submitted. Additionally, the fast track designation may be withdrawn by the FDA if the FDA believes that the designation is no longer supported by data emerging in the clinical trial process.

In some cases, either a breakthrough therapy or a fast-track-designated product candidate may also qualify for one or more of the following programs:

Priority review. Under FDA policies, a product candidate is eligible for priority review, or review within six months from the time a complete NDA is accepted for filing, if the product

candidate provides a significant improvement compared to marketed drugs in the treatment, diagnosis or prevention of a disease. Under PDUFA, the FDA is further entitled to take 60 days to determine that an application is sufficiently complete to allow the filing, therefore a priority review timetable may be 60 days before acceptance plus review. We cannot guarantee any of our product candidates will receive a priority review designation, or, if such a priority designation is received, that review or approval will be faster than conventional FDA procedures, or that the FDA will ultimately grant approval.

Accelerated approval. Under the FDA’s accelerated approval regulations, the FDA is authorized to approve product candidates that have been studied for their safety and effectiveness in treating serious or life-threatening illnesses, and that provide meaningful therapeutic benefit to patients over existing treatments based upon either a surrogate endpoint that is reasonably likely to predict clinical benefit or on the basis of an effect on a clinical endpoint other than patient survival. In clinical trials, surrogate endpoints are alternative measurements of the symptoms of a disease or condition that are substituted for measurements of observable clinical symptoms. A product candidate approved on this basis is subject to rigorous post-marketing compliance requirements, including the completion of Phase IV or post-approval clinical trials to validate the surrogate endpoint or confirm the effect on the clinical endpoint. Failure to conduct required post-approval studies, or to validate a surrogate endpoint or confirm a clinical benefit during post-marketing studies, will allow the FDA to withdraw the drug from the market on an expedited basis. All promotional materials for product candidates approved under accelerated regulations are subject to prior review by the FDA.

When appropriate, we intend to seek either breakthrough therapy, fast track designation, priority review or accelerated approval for our products. We cannot predict whether any of our products will obtain a breakthrough therapy, fast track, priority review or accelerated approval designation, or the ultimate impact, if any, of these designations on the approval process, on the timing, or the likelihood of FDA approval of any of our product candidates.

Orphan drug designation in the United States is designed to encourage sponsors to develop drugs intended for rare diseases or conditions. In the United States, a rare disease or condition is statutorily defined as a condition that affects fewer than 200,000 individuals in the United States or that affects more than 200,000 individuals in the United States and for which there is no reasonable expectation that the cost of developing and making available the drug for the disease or condition will be recovered from sales of the drug in the United States.

Orphan drug designation qualifies a company for tax credits and market exclusivity for seven years following the date of the drug’s marketing approval if granted by the FDA. An application for designation as an orphan product can be made any time prior to the filing of an application for approval to market the product. A drug becomes an orphan when it receives orphan drug designation from the Office of Orphan Products Development, or OOPD, at the FDA based on acceptable confidential requests made under the regulatory provisions. The drug must then go through the new drug approval process like any other drug. Orphan drug designations are decided solely by the OOPD staff, but the OOPD occasionally will request opinions from the Center for Drug Evaluation and Research, especially when dealing with issues such as the appropriateness of the requested indication or the scientific rationale described by the sponsor.

A sponsor may request orphan drug designation of a previously unapproved drug or new orphan indication for an already marketed drug. In addition, a sponsor of a drug that is otherwise the same drug as an already approved orphan drug may seek and obtain orphan drug designation for the subsequent drug for the same rare disease or condition if it can present a plausible hypothesis that its drug may be clinically superior to the first drug. More than one sponsor may receive orphan drug designation for the same drug for the same rare disease or condition, but each sponsor seeking orphan drug designation must file a complete request for designation.

Drisapersen was granted orphan drug designation in the United States in 2005. All of our other DMD development compounds (PRO044, PRO045, PRO053, PRO052 and PRO055) have also been granted orphan drug designation.

The period of exclusivity begins on the date that the marketing application is approved by the FDA and applies only to the indication for which the drug has been designated. The FDA could approve a second application for the same drug for a different use or a second application for a clinically superior version of the drug for the same use. The FDA cannot, however, approve the same drug made by another manufacturer for the same indication during the market exclusivity period unless it has the consent of the sponsor or the sponsor is unable to provide sufficient quantities.

In addition, under the FDCA, as amended by the Hatch-Waxman Act of 1984, or the Hatch-Waxman Act, a drug can be classified as a new chemical entity if the FDA has not previously approved any other new drug containing the same active agent. Under sections 505(c)(3)(D)(ii) and 505(j)(5)(D)(ii) of the FDCA, as amended by the Hatch-Waxman Act, the first applicant to gain approval of an NDA for a new chemical entity may, in the absence of patent protections, be eligible for five years of market exclusivity in the United States following regulatory approval.

During the five-year exclusivity period, the FDA may not accept for review an abbreviated new drug application, or a 505(b)(2) NDA submitted by a competitor for another version of such drug, where the applicant does not own or have a legal right of reference to all the data required for approval. Protection under the Hatch-Waxman Act will not prevent the filing or approval of another full NDA, but the applicant would be required to conduct its own adequate and well-controlled clinical trials to demonstrate safety and effectiveness. The Hatch-Waxman Act also provides three years of marketing exclusivity for an NDA, 505(b)(2) NDA or supplements to existing NDAs if new clinical investigations are essential to the approval of the applications, for example for new indications, dosages, or strengths of an existing drug. This three-year exclusivity covers only the conditions associated with the new clinical investigations and does not prohibit the FDA from approving abbreviated NDAs filed by competitors for drugs containing the original active agent.

The Hatch-Waxman Act also permits a patent restoration term of up to five years as compensation for the portion of a drug’s patent term lost during product development and the FDA regulatory review process. However, patent term restoration cannot extend the remaining term of a patent beyond a total of 14 years. The patent term restoration period is generally one-half the time between the effective date of an IND, and the submission date of an NDA, plus the time between the submission date of an NDA and the approval of that application. Only one patent applicable to an approved drug is eligible for the extension and it must be applied for

prior to expiration of the patent. The United States Patent and Trademark Office, in consultation with the FDA, reviews and approves the application for any patent term extension or restoration. In the future, we may consider applying for restorations of patent term for some of our currently owned or licensed patents to add patent life beyond the current expiration date, depending on the expected length of clinical trials and other factors involved in the filing of the relevant NDA.

If regulatory approval for marketing of a product or new indication for an existing product is obtained, we will be required to comply with all regular post-approval regulatory requirements as well as any post-approval requirements that the FDA have imposed as part of the approval process. We will be required to report certain adverse reactions and production problems to the FDA, provide updated safety and efficacy information and comply with requirements concerning advertising and promotional labeling requirements. Drug manufacturers and certain of their subcontractors are required to register their establishments with the FDA and certain state agencies, and are subject to periodic unannounced inspections by the FDA and certain state agencies for compliance with ongoing regulatory requirements, including current Good Manufacturing Practices regulations, which impose certain procedural and documentation requirements upon drug manufacturers. Accordingly, we and our third-party manufacturers must continue to expend time, money and effort in the areas of production and quality control to maintain compliance with current Good Manufacturing Practices regulations and other regulatory requirements. Discovery of problems with a product after approval for marketing may result in restrictions on a product, manufacturer, or holder of an approved NDA, including withdrawal of the product from the market.

The process regarding approval of medicinal products in the EU follows roughly the same lines as in the United States and likewise generally involves satisfactorily completing each of the following:

Pursuant to the Clinical Trials Directive 2001/20/EC, as amended, a system for the approval of clinical trials in the European Union has been implemented through national legislation of the member states. Under this system, approval must be obtained from the competent national authority of a European Union member state in which a study is planned to be conducted. To this end, a CTA is submitted, which must be supported by an investigational medicinal product dossier, or IMPD, and further supporting information prescribed by the Clinical Trials Directive and other applicable guidance documents. Furthermore, a clinical trial may only be started after a competent ethics committee has issued a favorable opinion on the clinical trial application in that country.

Clinical drug development is often described as consisting of four temporal phases (Phase I- IV), see for example EMA’s note for guidance on general considerations for clinical trials (CPMP/ICH/291/95).

Studies in Phase IV are all studies (other than routine surveillance) performed after drug approval and related to the approved indication.

The phase of development provides an inadequate basis for classification of clinical trials because one type of trial may occur in several phases. The phase concept is a description, not a set of requirements. The temporal phases do not imply a fixed order of studies since for some drugs in a development plan the typical sequence will not be appropriate or necessary.

Manufacturing of investigational products is subject to the holding of authorization and must be carried out in accordance with current Good Manufacturing Practices.

During the development of a medicinal product, frequent interactions with the EU regulators are vital to make sure all relevant input and guidelines/regulations are taken into account in the overall program. Prosensa has established an ongoing dialogue with EMA and certain national authorities by making use of the mechanisms that exist for interaction and input.

The regulation established the Paediatric Committee, or PDCO, which is responsible for coordinating the EMA’s activities regarding medicines for children. The PDCO’s main role is to determine all the studies that applicants need to do in the pediatric population as part of the so-called Paediatric Investigation Plans, or PIPs.

All applications for marketing authorization for new medicines that were not authorized in the EU before 26 January 2007 have to include the results of studies carried out in children of different ages. As indicated, the PDCO determines what these studies entail and describes them in a PIP. This requirement also applies when a company wants to add a new indication, pharmaceutical form or route of administration for a medicine that is already authorized.

Before a marketing authorization application can be filed, or an existing marketing authorization can be amended, the EMA checks that companies actually comply with the agreed studies and measures listed in each relevant PIP.

With the regulation coming into force, several incentives for the development of medicines for children also became available in the EU:

Since our compounds in the DMD portfolio are all intended for the use in children by the very nature of the disease, a PIP has been agreed for drisapersen licensed to GSK and we have additional PIP procedures ongoing with PDCO for the other programs in clinical development.

Authorization to market a product in the European Union member states proceeds under one of four procedures: a centralized authorization procedure, a mutual recognition procedure, a decentralized procedure or a national procedure.

The centralized authorization procedure is optional for other medicinal products if they contain a new active substance or if the applicant shows that the medicinal product concerned constitutes a significant therapeutic, scientific or technical innovation or that the granting of authorization is in the interest of patients at a European Community level.

Under the centralized authorization procedure, the CHMP serves as the scientific committee that renders opinions about the safety, efficacy and quality of human products on behalf of the EMA. The CHMP is composed of experts nominated by each member state’s national drug authority, with one of them appointed to act as Rapporteur for the co-ordination of the evaluation with the possible assistance of a further member of the Committee acting as a Co-Rapporteur. After approval, the Rapporteur(s) continue to monitor the product throughout its life cycle. The CHMP has 210 days, to adopt an opinion as to whether a marketing authorization should be granted. The process usually takes longer as additional information is requested, which triggers clock-stops in the procedural timelines. The process is complex and involves extensive consultation with the regulatory authorities of member states and a number of experts. Once the procedure is completed, a European Public Assessment Report, or EPAR, is produced. If the opinion is negative, information is given as to the grounds on which this conclusion was reached. The opinion produced by the CHMP is sent to the European Commission and used in reaching the final decision.

In general, if the centralized procedure is not followed, there are three alternative procedures. If marketing authorization in only one member state is preferred, an application can be filed with the national competent authority of a member state. The other two options are a mutual recognition by European Union member states and the decentralized procedure, both under Directive 2001/83. A marketing authorization may be granted only to an applicant established in the European Union.

It is not always possible for applicants to follow the national procedure. In the case of medicinal products in the category for which the centralized authorization procedure is compulsory, that procedure must be followed. In addition, the national procedure is not available in the case of medicinal product dossiers where the same applicant has already obtained marketing authorization in one of the other European Union member states or has already submitted an application for marketing authorization in one of the other member states and the application is under consideration. In the latter case, applicants must follow a mutual recognition procedure.

After a drug has been authorized and launched, it is a condition of maintaining the marketing authorization that all aspects relating to its quality, safety and efficacy must be kept under review. Sanctions may be imposed for failure to adhere to the conditions of the marketing authorization. In extreme cases, the authorization may be revoked, resulting in withdrawal of the product from sale.

When appropriate, we may seek accelerated assessment for our products. When an application is submitted for a marketing authorization in respect of a drug for human use which is of major interest from the point of view of public health and in particular from the viewpoint of therapeutic innovation, the applicant may request an accelerated assessment procedure pursuant to article 14, paragraph 9 of Regulation 726/2004.

As per Regulation EC 726/2004, Art. 14(7), a medicine that would fulfill an unmet medical need may, if its immediate availability is in the interest of public health, be granted a conditional marketing authorization on the basis of less complete clinical data than are normally required, subject to specific obligations being imposed on the authorization holder. These specific obligations are to be reviewed annually by the EMA. The list of these obligations shall be made publicly accessible. Such an authorization shall be valid for one year, on a renewable basis.

As per Regulation EC 726/2004, Art. 14(8), products for which the applicant can demonstrate that comprehensive data (in line with the requirements laid down in Annex I of Directive 2001/83/EC, as amended) cannot be provided (due to specific reasons foreseen in the legislation) might be eligible for marketing authorization under exceptional circumstances. This type of authorization is reviewed annually to reassess the risk-benefit balance. The fulfillment of any specific procedures/obligations imposed as part of the marketing authorization under exceptional circumstances is aimed at the provision of information on the safe and effective use of the product and will normally not lead to the completion of a full dossier/approval.

We cannot predict whether any of our products will obtain any of such designations or predict the ultimate impact, if any, of such designations on the timing, conditions or likelihood of EMA authorization.

Marketing authorization shall be valid for five years in principle and the marketing authorization may be renewed after five years on the basis of a re-evaluation of the risk-benefit balance by the EMA or by the competent authority of the authorizing member state. To this end, the marketing authorization holder shall provide the EMA or the competent authority with a consolidated version of the file in respect of quality, safety and efficacy, including all variations introduced since the marketing authorization was granted, at least six months before the marketing authorization ceases to be valid. Once renewed, the marketing authorization shall be valid for an unlimited period, unless the Commission or the competent authority decides, on justified grounds relating to pharmacovigilance, to proceed with one additional five-year renewal. Any authorization which is not followed by the actual placing of the drug on the EU market (in case of centralized procedure) or on the market of the authorizing member state within three years after authorization shall cease to be valid (the so-called sunset clause).

Regulation 141/2000 states that a drug shall be designated as an orphan drug if its sponsor can establish:

An application for designation as an orphan product can be made any time prior to the filing of an application for approval to market the product. Marketing authorization for an orphan drug leads to a ten-year period of market exclusivity. This period may, however, be reduced to six years if, at the end of the fifth year, it is established that the product no longer meets the criteria for orphan drug designation, for example because the product is sufficiently profitable not to justify market exclusivity. Market exclusivity can be revoked only in very selected cases, such as consent from the marketing authorization holder, inability to supply sufficient quantities of the product, demonstration of “clinically relevant superiority” by a similar medicinal product, or, after a review by the Committee for Orphan Medicinal Products, requested by a member state in the fifth year of the marketing exclusivity period (if the designation criteria are believed to no longer apply). Medicinal products designated as orphan drugs pursuant to Regulation 141/2000

shall be eligible for incentives made available by the European Community and by the member states to support research into, and the development and availability of, orphan drugs.

We have applied for and been granted orphan status in the EU for all compounds in our portfolio which are intended for the treatment of DMD.

Without prejudice to the law on the protection of industrial and commercial property, all applications for marketing authorization receive an 8+2+1 protection regime.

This regime consists of a regulatory data protection period of eight years plus a concurrent market exclusivity of ten years plus an additional market exclusivity of one further year if, during the first eight years of those ten years, the marketing approval holder obtains an approval for one or more new therapeutic indications which, during the scientific evaluation prior to their approval, are determined to bring a significant clinical benefit in comparison with existing therapies. Under the current rules, a third party may reference the preclinical and clinical data of the original sponsor beginning eight years after first approval, but the third party may market a generic version after only ten (or eleven) years have lapsed.

As indicated, additional data protection can be applied for when an applicant has complied with all requirements as set forth in an approved PIP.

The manufacturing of authorized drugs, for which a separate manufacturer’s license is mandatory, must be conducted in strict compliance with the EMA’s current Good Manufacturing Practices requirements and comparable requirements of other regulatory bodies, which mandate the methods, facilities and controls used in manufacturing, processing and packing of drugs to assure their safety and identity. The EMA enforces its current Good Manufacturing Practices requirements through mandatory registration of facilities and inspections of those facilities. The EMA may have a coordinating role for these inspections while the responsibility for carrying them out rests with the member states competent authority under whose responsibility the manufacturer falls. Failure to comply with these requirements could interrupt supply and result in delays, unanticipated costs and lost revenues, and could subject the applicant to potential legal or regulatory action, including but not limited to warning letters, suspension of manufacturing, seizure of product, injunctive action or possible civil and criminal penalties.

The marketing and promotion of authorized drugs, including industry-sponsored continuing medical education and advertising directed toward the prescribers of drugs and/or the general public, are strictly regulated in the European Community notably under Directive 2001/83 in the European Community code relating to medicinal products for human use as amended by Directive 2004/27. The applicable regulation aims to ensure that information provided by holders of marketing authorizations regarding their products is truthful, balanced and accurately reflects the safety and efficacy claims authorized by the EMA or by the competent authority of the authorizing member state. Failure to comply with these requirements can result in adverse publicity, warning letters, corrective advertising and potential civil and criminal penalties.

We and the operations of our CMOs are further subject to various foreign, national, federal, state and local laws and regulations relating to environmental, health and safety matters, including the handling, disposal, release, and use of and maintenance of a registry for hazardous materials, among others. Although we do not believe that we will be required to make material operating or capital expenditures in connection with such laws and regulations, we may be required to incur significant costs to comply with these laws and regulations in the future, and complying with these laws and regulations may result in a material adverse effect upon our business, financial condition and results of operations. Further, our failure or the failure of our CMOs to comply with such laws and regulations could have a material adverse effect on our business and reputation, result in an interruption or delay in the development or manufacture of our products, or increase the costs for the development or manufacture of our products.

Significant uncertainty exists as to the coverage and reimbursement status of any drug products for which we obtain regulatory approval, including the products being developed and potentially commercialized by GSK. Sales of any of our product candidates or GSK’s licensed product candidates under our collaboration, if approved, will depend, in part, on the extent to which the costs of the products will be covered by third-party payors, including government health programs such as Medicare and Medicaid, commercial health insurers and managed care organizations. The process for determining whether a payor will provide coverage for a drug product may be separate from the process for setting the price or reimbursement rate that the payor will pay for the drug product once coverage is approved. Third party payors may limit coverage to specific drug products on an approved list, or formulary, which might not include all of the approved drugs for a particular indication.

In order to secure coverage and reimbursement for any product that might be approved for sale, we or GSK, as applicable, may need to conduct pharmacoeconomic studies in order to demonstrate the medical necessity and cost-effectiveness of the product, in addition to the costs required to obtain FDA or other comparable regulatory approvals. Our product candidates or GSK’s licensed product candidates may not be considered medically necessary or cost-effective. A payor’s decision to provide coverage for a drug product does not imply that an adequate reimbursement rate will be approved. Third party reimbursement may not be sufficient to enable us to maintain price levels high enough to realize an appropriate return on our investment in product development.

The containment of healthcare costs has become a priority of governments, and the prices of drugs have been a focus in this effort. Third party payors are increasingly challenging the prices charged for medical products and services and examining the medical necessity and cost-effectiveness of medical products and services, in addition to their safety and efficacy. If these third-party payors do not consider our products to be cost-effective compared to other available therapies, they may not cover our products after approval as a benefit under their plans or, if they do, the level of payment may not be sufficient to allow us to sell our products at a profit. The U.S. government, state legislatures and non-U.S. governments have shown significant interest in implementing cost containment programs to limit the growth of government-paid health care costs, including price controls, restrictions on reimbursement and requirements for substitution of generic products for branded prescription drugs. Adoption of such controls and

measures, and tightening of restrictive policies in jurisdictions with existing controls and measures, could limit payments for pharmaceuticals such as the product candidates that we are developing and could adversely affect our net revenue and results.

Pricing and reimbursement schemes vary widely from country to country. Some countries provide that drug products may be marketed only after a reimbursement price has been agreed. Some countries may require the completion of additional studies that compare the cost-effectiveness of a particular product candidate to currently available therapies. For example, the European Union provides options for its member states to restrict the range of drug products for which their national health insurance systems provide reimbursement and to control the prices of medicinal products for human use. European Union member states may approve a specific price for a drug product or may instead adopt a system of direct or indirect controls on the profitability of the company placing the drug product on the market. Other member states allow companies to fix their own prices for drug products, but monitor and control company profits. The downward pressure on health care costs in general, particularly prescription drugs, has become very intense. As a result, increasingly high barriers are being erected to the entry of new products. In addition, in some countries, cross-border imports from low-priced markets exert competitive pressure that may reduce pricing within a country. There can be no assurance that any country that has price controls or reimbursement limitations for drug products will allow favorable reimbursement and pricing arrangements for any of our products.

The marketability of any products for which we or GSK with respect to the product candidates it licenses under our collaboration receive regulatory approval for commercial sale may suffer if the government and third-party payors fail to provide adequate coverage and reimbursement. In addition, emphasis on managed care in the United States has increased and we expect will continue to increase the pressure on drug pricing. Coverage policies, third-party reimbursement rates and drug pricing regulation may change at any time. In particular, the Patient Protection and Affordable Care Act was enacted in the United States in March 2010 and contains provisions that may reduce the profitability of drug products, including, for example, increased rebates for drugs sold to Medicaid programs, extension of Medicaid rebates to Medicaid managed care plans, mandatory discounts for certain Medicare Part D beneficiaries and annual fees based on pharmaceutical companies’ share of sales to federal health care programs. Even if favorable coverage and reimbursement status is attained for one or more products for which we or GSK receive regulatory approval, less favorable coverage policies and reimbursement rates may be implemented in the future.

We lease approximately 20,000 square feet of office and laboratory space in Leiden, the Netherlands. This facility serves as our corporate headquarters and central laboratory facility. We believe that our existing facilities are adequate to meet our current needs, and that suitable additional alternative spaces will be available in the future on commercially reasonable terms.

As of March 31, 2013, we had 85 employees, 24 of whom hold M.D. or Ph.D. degrees. None of our employees is subject to a collective bargaining agreement or represented by a trade or labor union. We are in the process of establishing a workers’ council for our employees. We consider our relations with our employees to be good.

From time to time we are involved in legal proceedings that arise in the ordinary course of business. We believe that the outcome of these proceedings, if determined adversely to us, will not have a material adverse effect on our financial position. During the period covered by the audited and approved financial statements contained herein, we have not been a party to or paid any damages in connection with litigation that has had a material adverse effect on our financial position. No assurance can be given that future litigation will not have a material adverse effect on our financial position.

Below is a summary of relevant information concerning our management board, our supervisory board, senior management and other employees as well as a brief summary of certain significant provisions of Dutch corporate law, the Articles of Association that will be in effect upon the consummation of this offering and the Dutch Corporate Governance Code, or DCGC, in respect of our management board and supervisory board.

We are currently reviewing the composition of our boards and our corporate governance practices in light of this offering and applicable requirements of the SEC and Nasdaq. In subsequent filings with the SEC, we will update any relevant disclosure as appropriate.

We have a two-tier board structure consisting of our supervisory board (raad van commissarissen) and a separate management board (raad van bestuur).

Our supervisory board supervises the policies of the management board and the general course of the affairs of our business. The supervisory board gives advice to the management board and is guided by the interests of the business when performing its duties. The management board provides the supervisory board with such necessary information as is required to perform its duties. Supervisory directors are appointed by the general meeting of shareholders upon a binding nomination of the supervisory board for a term of up to four years. The binding nomination will be prepared by the nominating and corporate governance committee.

Our Articles of Association provide for a term of appointment of supervisory directors of up to four years. The current supervisory directors may be appointed for different terms as a result of which only approximately one-fourth of our supervisory board members will be subject to election in any one year. Such an appointment would have the effect of creating a staggered board and may deter a takeover attempt.

The supervisory board meets as often as a supervisory board member deems necessary. In a meeting of the supervisory board, each supervisory director has a right to cast one vote. All resolutions by the supervisory board are adopted by an absolute majority of the votes cast. In the event the votes are equally divided, the chairman has a decisive vote. A supervisory director may grant another supervisory director a written proxy to represent him at the meeting, but a supervisory director cannot represent more than one supervisory director.

Our supervisory board can pass resolutions outside of meetings, provided that the resolution is adopted in writing and all supervisory directors have consented to adopting the resolution outside of a meeting. The chairman shall prepare and sign a report of the resolutions adopted in this manner.

Our supervisory directors do not have a retirement age requirement under our Articles of Association. The current members of our supervisory board were elected at a shareholders’ meeting held on , 2013.

The following table presents the names of the current members of our supervisory board.

The following is a brief summary of the business experience of the members of our supervisory board. Unless otherwise indicated, the current business address for the members of our supervisory board is J.H. Oortweg 21, 2333 CH Leiden, the Netherlands.

Daan Ellens is chairman of our supervisory board and has served on the board since 2007. Dr. Ellens also serves as chairman of the supervisory board of Hybrigenics SA, Zealand Pharma A/S. and Kreatech Holding B.V. Prior to these positions, Dr. Ellens was Chief Executive Officer of Rhein Biotech N.V. from 1994 to 2002. Dr. Ellens holds a Ph.D. degree in molecular biology from the University of Utrecht in the Netherlands and a M.B.A. degree from the University Eindhoven, the Netherlands. Dr. Ellens’ extensive and successful track record as one of the most successful European biotechnology entrepreneurs adds significant value to our team. We believe that Dr. Ellens is qualified to serve on our supervisory board because of his career in the pharmaceutical industry, including his extensive experience as an entrepreneur and executive and his service on the boards of directors of other biopharmaceutical companies.

Stephen Bunting has served on our supervisory board since 2007. Dr. Bunting has been the managing partner of Abingworth since 2002 and has over 30 years of experience in the venture capital business. Dr. Bunting has served on the boards of a number of life science companies including Ablynx N.V., Astex Technologies, Aurora Biosciences Inc., Devgen N.V., Galapagos N.V. and Genetic Therapy Inc. Dr. Bunting holds a Ph.D. degree from the University of Reading in biological sciences. Dr. Bunting was nominated to serve on our board by Abingworth, one of our shareholders. We believe that Dr. Bunting is qualified to serve on our supervisory board because of his extensive experience as a venture capital investor and his service on the boards of directors of biopharmaceutical companies in the United States and Europe. These experiences allow him to provide the board with insight into a broad range of issues related to our business activities at this stage in our development.

Rémi Droller has served on our supervisory board since 2008. Mr. Droller is a managing partner at Kurma Life Sciences Partners, which he joined in September 2010. Mr. Droller was previously with CDC Innovation from 2000 to 2003 and with AGF Private Equity SA (now Idinvest Partners) from 2003 to 2010 where he was in charge of the development of the life sciences investment activity. During this period, Mr. Droller served on the board of several investee companies such as Adocia S.A.S., AM Pharma Holding B.V., BioAlliance Pharma S.A., Domain Therapeutics S.A., IntegraGen S.A., Novagali Pharma S.A., STAT Diagnostica S.L. and Zealand Pharma A.V. Mr. Droller holds a master’s degree in molecular biology from Paris VI University and a master’s degree in finance and innovation management from Masternova – AgroParisTech. Mr. Droller was nominated to serve on our board by Idinvest Partners, one of our shareholders. We believe that Mr. Droller is qualified to serve on our supervisory board because of his extensive experience as a venture capital investor and his service on the boards of directors of other biopharmaceutical companies.

Peter Goodfellow has served on our supervisory board since 2008 and is also a member of our scientific advisory board. Dr. Goodfellow was formerly Senior Vice President for Discovery Research at GlaxoSmithKline plc from 1998 to 2006. In addition, Dr. Goodfellow serves as a director of the Institute of Cancer Research and as a member of several advisory boards, including the Scientific Advisory Board of the Institute of Molecular and Cell Biology, the Gates Foundation Discovery Board and Sanofi’s Strategic Development and Scientific Advisory Council. He has also held the Balfour chair in genetics at Cambridge University and research positions at the Imperial Cancer Research Fund. Dr. Goodfellow holds bachelor’s and doctorate degrees from the University of Bristol and a doctorate degree from Oxford University. We believe that Dr. Goodfellow is qualified to serve on our supervisory board because of his career in the pharmaceutical industry, including his extensive experience as an executive and service on the boards of directors of other biopharmaceutical companies.

Martijn Kleijwegt has served on our supervisory board since 2008. Mr. Kleijwegt founded Life Sciences Partners in 1998 and has been managing partner of Life Sciences Partners since then. Mr. Kleijwegt has served on the boards of a number of companies including Qiagen N.V., Rhein Biotech N.V., Crucell N.V., Movetis N.V. and Pronota N.V. Mr. Kleijwegt graduated from the University of Amsterdam with a degree in economics. Mr. Kleijwegt was nominated to serve on our board by Life Sciences Partners, one of our shareholders. We believe that Mr. Kleijwegt is qualified to serve on our supervisory board because of his experience in the biopharmaceutical industry as a venture capital investor, a founder of Life Sciences Partners and a member of the boards of directors of other biopharmaceutical companies.

David Mott has served on our supervisory board since 2012. Mr. Mott has served as a general partner of New Enterprise Associates, an investment firm focused on venture capital and growth equity investments, since September 2008, where he leads the healthcare investing practice. Prior to joining NEA, Mr. Mott was President and Chief Executive Officer of MedImmune LLC, subsidiary of AstraZeneca plc, and Executive Vice President of AstraZeneca plc. From 1992 to 2008, Mr. Mott worked at MedImmune Limited and served in numerous roles during his tenure including Chief Operating Officer, Chief Financial Officer, President and Chief Executive Officer. Prior to joining MedImmune, Mr. Mott was a Vice President in the Health Care Investment Banking Group at Smith Barney, Harris Upham & Co. Inc. Mr. Mott is currently Chairman of 3-V Biosciences, Inc., TESARO, Inc., and Zyngenia, Inc. and is a director of Ardelyx, Inc., Epizyme, Inc., and Omthera Pharmaceuticals, Inc. Mr. Mott also serves on the governing board of St. Albans School. Mr. Mott received a bachelor of arts degree from Dartmouth College. Mr. Mott was nominated to serve on our board by New Enterprise Associates, one of our shareholders. We believe that Mr. Mott is qualified to serve on our supervisory board because of his experience as a venture capital investor, his experience in the pharmaceutical industry and his service on the boards of directors of other biopharmaceutical companies.

Jim Van heusden has served on our supervisory board since 2008. Dr. Van heusden has been a partner in venture capital at Gimv N.V. since 2001 and focuses on investments in life sciences. Dr. Van heusden currently serves on the board of Pronota N.V. and has been a board member at Ablynx, ActoGeniX, CropDesign and Multiplicom. Prior to joining Gimv N.V., Dr. Van heusden worked as a senior scientist at Janssen Pharmaceutica N.V., a Johnson & Johnson company, where he also served on the research management committee of the collaboration with Rigel Pharmaceuticals. Dr. Van heusden holds bachelor’s and master’s degrees in chemistry and biochemistry from the University of Antwerp and a Ph.D. degree in molecular and cellular biology from the University of Maastricht. Dr. Van heusden was nominated to serve on our

board by Gimv N.V., one of our shareholders. We believe that Mr. Van heusden is qualified to serve on our supervisory board because of his experience as a venture capital investor, his experience in the pharmaceutical industry and his service on the boards of directors of other biopharmaceutical companies.

The management board is in charge of managing us under the supervision of the supervisory board.

The supervisory board determines the number of managing directors. Managing directors are appointed by the general meeting of shareholders upon a binding nomination of the supervisory board for a term of up to four years.

At least once per year the management board informs the supervisory board in writing of the main lines of our strategic policy, the general and financial risks and the management and control system.

We have a strong centralized management board led by Hans Schikan, our Chief Executive Officer, with broad experience in general management, strategy, corporate development, operations, in particular the commercialization of orphan drugs for rare diseases, information technology, finance, sales, communications and training. Many of our managing directors have worked together as a team for many years.

The following is a brief summary of the business experience of the members of our management board. Unless otherwise indicated, the current business addresses for the members of our management board is J.H. Oortweg 21, 2333 CH Leiden, the Netherlands.

Hans Schikan has served as our Chief Executive Officer since January 2009. Mr. Schikan has more than 25 years of senior managerial experience in the pharmaceutical and biotechnology industries. From May 2004 until January 2009, Mr. Schikan worked at Genzyme Corporation in various executive roles, including Vice President of Global Marketing and Strategic Development for its rare genetic disease franchise. In this position he oversaw the launch of various orphan drugs globally. Prior to Genzyme, Mr. Schikan worked at Organon International from 1986 to 2004 in various senior business roles across different geographies, including managing director positions in multiple countries. Mr. Schikan also serves as Non-executive Director of Swedish Orphan Biovitrum A.B., Executive Board Member of the Dutch Top Institute Pharma, and Member of the Core Team of the Dutch Top Sector Life Sciences & Health. He is also past Chairman of Nefarma, the Dutch Association of Research Based Pharmaceutical Industry. Mr. Schikan holds a Pharm.D. degree from the University of Utrecht, the Netherlands.

Giles Campion has served as our Chief Medical Officer and Senior Vice-President of Research and Development since May 2009. Board certified in rheumatology, Dr. Campion has more than twenty years of experience in the pharmaceutical and biotechnology industries and is an expert in translational medicine. From 2005 to 2008, Dr. Campion was head of global medicine, GE Healthcare. Dr. Campion has held posts of increasing seniority in both large pharmaceutical and biotechnology companies working in Europe and the United States, covering many different therapeutic areas. Dr. Campion holds a bachelor’s and doctorate degree in medicine from the University of Bristol.

Luc Dochez has served as our Chief Business Officer and Senior Vice-President of Business Development since November 2008. Mr. Dochez has over 15 years of experience in the biotechnology industry. Before joining Prosensa, Mr. Dochez was a consultant within Arthur D. Little’s biotechnology practice from 1998 to 2001, Director of Business Development at Methexis Genomics N.V. from 2001 to 2002, Vice President of Business Development at TiGenix N.V. from 2002 to 2008 and President of TiGenix Inc. from 2007 to 2008. Mr. Dochez holds a Pharm.D. degree from the University of Leuven, a postgraduate degree in business economics from the same university and a M.B.A. degree from Vlerick Management School. Mr. Dochez is currently an independent supervisory board member at Ovizio S.A.

Berndt Modig has served as our Chief Financial Officer since March 2010. Mr. Modig has more than twenty-five years of international experience in finance and operations, private equity and mergers and acquisitions. Before joining Prosensa, Mr. Modig was Chief Financial Officer at Jerini AG from October 2003 to November 2008, where he directed private financing rounds, its initial public offering in 2005 and its acquisition by Shire plc in 2008. Prior to Jerini, Mr. Modig served as Chief Financial Officer at Surplex AG from 2001 to 2003 and as Finance Director Europe of U.S.-based Hayward Industrial Products Inc. from 1999 to 2001. In previous positions, Mr. Modig was a partner in the Brussels-based private equity firm Agra Industria from 1994 to 1999 and a Senior Manager in the Financial Services Industry Group of Price Waterhouse LLP in New York from 1991 to 1994. Mr. Modig served as a director of Mobile Loyalty plc from 2012 to 2013. Mr. Modig has a bachelor’s degree in business administration, economics and German from the University of Lund, Sweden and a M.B.A. degree from INSEAD, France and is a Certified Public Accountant.

The audit committee, which is expected to consist of , and , will assist the supervisory board in overseeing our accounting and financial reporting processes and the audits of our financial statements. The audit committee will consist exclusively of members of our supervisory board who are financially literate, and is considered an “audit committee financial expert” as defined by the SEC. In addition, under SEC and Nasdaq rules, there are heightened independence standards for members of the audit committee, including a prohibition against the receipt of any compensation from us other than standard supervisory director fees. All of our expected audit committee members will meet this heightened standard. The audit committee will be governed by a charter that complies with Nasdaq rules.

Upon the completion of this offering, the audit committee will be responsible for:

The audit committee will meet as often as one or more members of the audit committee deem necessary, but in any event will meet at least four times per year. The audit committee will meet at least once per year with our independent accountant, without our management board being present.

The compensation committee, which is expected to consist of , and , will assist the supervisory board in determining management board compensation. The committee will recommend to the supervisory board for determination the compensation of each of our managing directors. Under SEC and Nasdaq rules, there are heightened independence standards for members of the compensation committee, including a prohibition against the receipt of any compensation from us other than standard supervisory director fees. All of our expected compensation committee members will meet this heightened standard.

Upon the completion of this offering, the compensation committee will be responsible for:

The nominating and corporate governance committee, which is expected to consist of , and , will assist our supervisory board in identifying individuals qualified to become members of our supervisory board and management board consistent with criteria established by our supervisory board and in developing our corporate governance principles.

Upon the completion of this offering, the nominating and corporate governance committee will be responsible for:

We intend to adopt a Code of Business Conduct and Ethics which covers a broad range of matters including the handling of conflicts of interest, compliance issues and other corporate policies such as insider trading and equal opportunity and non-discrimination standards.

We have entered into management services agreements with each of our managing directors. The management services agreements contain a termination notice period of . All of the management services agreements provide that the managing director may be terminated in the event of an urgent reason (dringende reden) at any time, without advance notice. Each management services agreement provides for severance pay upon (i) a termination of the managing director’s employment without cause, (ii) the resignation of the managing director within 12 months following a change in control event or (iii) or at the end of their term of appointment, unless the managing director is re-appointed. For termination without cause,

this severance pay is calculated based on that managing director’s annual remuneration. The management services agreements for Giles Campion, Luc Dochez and Berndt Modig provide for severance pay upon a termination of the managing director’s employment by us without cause in the amount of 50% of their annual remuneration. The management services agreement for Hans Schikan provides for severance pay upon termination of his employment by us without cause in the amount of 100% of his annual remuneration. Each management services agreement provides for a lump-sum payment following a change in control subject to certain conditions. That payment is equal to 130% of the individual’s annual gross fixed salary in effect at the time of the change in control for Giles Campion, Luc Dochez and Berndt Modig and 150% for Hans Schikan. This offering is not expected to constitute a change of control under the agreements. The management services employment agreements contain post-termination restrictive covenants, including post-termination non-competition and non-solicitation covenants. These covenants typically last for a period of at least six months post-termination.

Pursuant to each of the 2004 Employee Stock Option Plan, the 2006 Employee Stock Option Plan, the 2007 Employee Stock Option Plan and the 2010 Equity Incentive Plan (collectively, the “Incentive Plans”), our officers, employees, consultants and other eligible persons as described in the Incentive Plans may be granted the right to acquire (non-voting) depositary receipts (“Depositary Receipts”) issued in respect of our ordinary shares.

Upon the exercise of an option right, ordinary shares are issued to a Dutch foundation called Stichting Administratiekantoor Prosensa Holding (the “Foundation”), whose purpose is to facilitate administration of share-based compensation awards and pool the voting interests of the underlying shares. The Foundation thereupon grants a Depository Receipt for each issued ordinary share to the person exercising its option right. The Depositary Receipt holder is entitled to any dividends or other distributions paid on the ordinary shares for which the Depositary Receipts are granted. The voting rights attached to the ordinary shares are exercised by the Foundation. The Depositary Receipt holders are not entitled to attend a general meeting of shareholders or to cast a vote. The voting rights attached to the ordinary shares are exercised by the Foundation at its own discretion.

Board members of the Foundation are appointed by our supervisory board. The board consists of at least three board members. Currently, one board member is appointed on the binding nomination of the joint meeting of holders of Class A and Class B preferred shares. A second board member is appointed on the binding nomination of the general meeting of shareholders. The third board member is an employee.

In 2010 we established the 2010 Equity Incentive Plan (“the 2010 Plan”) with the purpose of advancing the interests of our shareholders by enhancing our ability to attract, retain and motivate individuals who are expected to make important contributions to us and by providing those persons with performance-based incentives that are intended to better align their interests with those of our shareholders.

Subject to adjustment for changes in ordinary shares due to changes in capitalization or reorganization events, Awards may be made under the 2010 Plan for up to 1,750,000 Depositary

Receipts issued by the Foundation with respect to the ordinary shares. As of the date of this prospectus, we have granted Awards under the 2010 Plan covering 1,397,630 shares.

Plan Administration. The 2010 Plan is administered by our management board. Approval of the supervisory board is required for all aggregate and significant individual grants of Awards under the 2010 Plan and the terms and conditions of exercise, vesting, purchase or repurchase in relation thereto.

Eligibility. All of our employees, officers and directors, as well as consultants and advisors, members of the supervisory board and members of advisory committees are eligible to be granted Awards. Awards include Options, SARs, Restricted Shares and Other Stock-Based Awards (each as defined below) under the 2010 Plan.

Subject to the approval of the supervisory board, the management board may grant options to purchase Depositary Receipts (“Options”) and determine the number of Depositary Receipts to be covered by each Option, the exercise price of each Option and the conditions and limitations applicable to the exercise of each Option, including conditions relating to applicable securities laws, as it considers necessary or advisable. We grant Options with only service-based vesting conditions or with service-based vesting conditions combined with vesting conditions subject to a liquidity event. With respect to Options with only service-based vesting conditions, 25% of the Depositary Receipts underlying the Options vest on the first anniversary of the grant date, and 2.0833% vest monthly thereafter. With respect to Options with service-based vesting conditions combined with vesting conditions subject to an initial public offering, 25% of the Depositary Receipts underlying the Options vest upon specified price thresholds of our ordinary shares, and 2.0833% vest monthly thereafter.

Approval of the supervisory board is required for all aggregate and significant individual grants of Awards under the 2010 Plan. Subject to the approval of the supervisory board, the management board establishes the exercise price of each Option and specifies the exercise price in the applicable Option agreement, which may be less than, equal to, or greater than the fair market value per ordinary share on the date the Option is granted. For purposes of the 2010 Plan, the fair market value per ordinary share is determined by (or in a manner approved by) the management board. Each Option is exercisable at such times and subject to such terms and conditions as the management board may specify in the applicable Option agreement with a maximum term of ten years.

Subject to the approval of the supervisory board, the management board may grant awards consisting of Stock Appreciation Rights (“SARs”) entitling the holder, upon exercise, to receive an amount of Depositary Receipts or cash or a combination thereof determined by reference to appreciation, from and after the date of grant, in the fair market value of an ordinary share over the measurement price established by the management board. The management board establishes the measurement price of each SAR and specifies it in the applicable SAR agreement pursuant to an applicable formula. The measurement price may not be less than 100% of the fair market value on the date the SAR is granted. Each SAR is exercisable at such times and subject to

such terms and conditions as the management board may specify in the applicable SAR agreement with a maximum term of ten years. We have never issued SARs.

Subject to the approval of the supervisory board, the management board may grant Awards entitling recipients to acquire Depositary Receipts (“Restricted Shares”), subject to our right to repurchase all or part of such Depositary Receipts at their issue price or other stated or formula price from the recipient in the event that conditions specified by the management board in the applicable Award are not satisfied prior to the end of the applicable restriction period or periods established by the management board for such Award. The management board determines the terms and conditions of a Restricted Share Award, including the conditions for vesting and repurchase (or forfeiture) and the issue price, if any. A holder of Restricted Shares has no voting rights with respect to such shares.

Other Awards of Depositary Receipts, and other Awards that are valued in whole or in part by reference to, or are otherwise based on, Depositary Receipts or other property, may be granted to participants (“Other Stock-Based Awards”). Such Other Stock-Based Awards are also available as a form of payment in the settlement of other Awards granted under the 2010 Plan or as payment in lieu of compensation to which a participant is otherwise entitled. Other Stock-Based Awards may be paid in Depositary Receipts or cash, as the Management Board determines. The management board determines the terms and conditions of each Other Stock-Based Award, including the conditions for vesting and repurchase and the issue price, if any.

Amendment. Subject to the approval of our shareholders and the supervisory board, we may amend, suspend or terminate the 2010 Plan or any portion thereof at any time. Unless otherwise specified in the amendment, any amendment to the 2010 Plan shall apply to, and be binding on the holders of, all Awards outstanding under the 2010 Plan at the time the amendment is adopted, provided the supervisory board determines that such amendment, taking into account any related action, does not materially and adversely affect the rights of participants under the 2010 Plan. In addition, we may from time to time establish one or more sub-plans under the 2010 Plan for purposes of satisfying applicable securities, tax or other laws of various jurisdictions.

Lock-up. The documentation evidencing each Award requires a participant, in connection with the initial underwritten public offering of the ordinary shares on a recognized stock exchange, (i) not to (a) enter into a potential transfer with respect to any shares of our ordinary shares or any other securities or (b) enter into any swap or other agreement that transfers, in whole or in part, any of the economic consequences of ownership of our ordinary shares or other securities during a specified period and (ii) to exercise any agreement reflecting clause (i) above as may be requested by us or the managing underwriters at the time of such offering.

In 2007 we established our 2007 Employee Stock Option Plan (as amended and restated in 2010, the “2007 Plan”), in 2006 we established our 2006 Employee Stock Option Plan (the “2006 Plan”) and in 2004 we established our 2004 Employee Stock Option Plan (the “2004 Plan,” and together with the 2007 Plan and the 2006 Plan, the “Prior Plans”). Each of the Prior Plans permits the

grant of options (“Options”) to purchase Depositary Receipts of an ordinary share. The Options are subject to transfer restrictions.

Plan Administration. Under each of the Prior Plans, an Option will be granted with the approval of the supervisory board and is evidenced by an Option agreement signed by the participant to indicate his acceptance of its terms and conditions. We do not intend to issue any future Options under any of the Prior Plans.

Eligibility. Under the 2006 Plan, Options may only be granted to an employee or a supervisory board member. Under the 2007 Plan and 2004 Plan, Options may be granted to an employee, a supervisory board member or a scientific advisory board member.

Option Exercise Price. The exercise price to acquire one Depositary Receipt upon exercise of an Option is determined by the management board in its sole discretion upon granting the Options. The exercise prices for currently granted and un-exercised Options under the Prior Plans range from €0.01 to €2.54.

Vesting Period. Under each of the Prior Plans, the option period commences at the date of grant and lasts ten years. Under the 2007 Plan, generally 25% of the Depositary Receipts underlying Options vest on the first anniversary of the grant date, and 2.0833% vest monthly thereafter. Under each of the 2006 Plan and the 2004 Plan, generally all the Depositary Receipts underlying Options vested immediately, with us having the right to repurchase a portion of the underlying Depositary Receipts if the employee or supervisory board member left within four years of the grant date.

Amendment. Subject to the approval of our shareholders and the supervisory board, we are authorized to amend each of the Prior Plans at any time and in any manner we deem fit. Amendments will in no event prejudice the existing rights of a participant, unless that participant consents to the amendments in writing. Each of the 2004 Plan, the 2006 Plan and, subject to the approval of the supervisory board, the 2007 Plan may be terminated by a resolution of the general meeting of shareholders.

Dutch law provides that we must establish a policy in respect of the remuneration of the members of our management board. The remuneration policy was adopted by the general meeting of shareholders on , 2013 on the proposal of the supervisory board. The supervisory board determines the remuneration of the management directors in accordance with the remuneration policy. A proposal by the supervisory board with respect to remuneration schemes in the form of shares or rights to shares is submitted by the supervisory board to the general meeting of shareholders for its approval. This proposal must set out at least the maximum number of shares or rights to shares to be granted to members of the management board and the criteria for granting or amendment. For the year ended December 31, 2012, we paid members of our management board an aggregate of €1,215,000 in compensation and benefits in kind (excluding bonuses) and an aggregate of €318,000 in bonuses. The bonuses to the managing directors are discretionary and are set by our supervisory board. For the year ended December 31, 2012, we also granted to the managing directors 100,000 Restricted Shares, 20,000 Options subject service-based vesting, and 1.0 million Options subject to service-based vesting combined with vesting upon a liquidity event such as a change of control or initial public offering. In the event of our initial public offering, the number of such options granted is automatically reduced from 1.0 million to

800,000. See “Management’s discussion and analysis of financial condition and results of operations—Share-based compensation—Share options.”

The general meeting of shareholders determines the compensation of the supervisory directors. Our Compensation Committee is in place to aid in such determination. For the year ended December 31, 2012, we paid an aggregate of €50,000 in compensation to Daan Ellens and Peter Goodfellow for their service as supervisory directors. Dr. Goodfellow also received compensation of €7,000 in connection with consulting services provided to us in 2012. The supervisory directors who were nominated by our venture capital investors did not receive any remuneration. Supervisory directors are, however, entitled to be reimbursed for their reasonable expenses incurred in attending meetings of the supervisory board or in otherwise acting for us. In addition, supervisory directors are entitled to receive share-based compensation subject to service-based vesting. For the year ended December 31, 2012, supervisory directors were granted 11,250 Options and 15,000 Restricted Shares.

The total amount set aside or accrued by us to provide pension, retirement or similar benefits for our managing directors and supervisory directors for the year ended December 31, 2012 was €0.

Managing directors and supervisory directors have the benefit of indemnification provisions in our Articles of Association. These provisions give managing directors and supervisory directors the right, to the fullest extent permitted by law, to recover from us amounts, including but not limited to litigation expenses, and any damages they are ordered to pay, in relation to acts or omissions in the performance of their duties. However, there is generally no entitlement to indemnification for acts or omissions that amount to willful (opzettelijk), intentionally reckless (bewust roekeloos) or seriously culpable (ernstig verwijtbaar) conduct. In addition, we have entered into agreements to indemnify managing directors and supervisory directors against expenses and liabilities to the fullest extent permitted by law. These agreements also provide, subject to certain exceptions, for indemnification for related expenses including, among others, attorneys’ fees, judgments, penalties, fines and settlement amounts incurred by any of these individuals in any action or proceeding. In addition to such indemnification, we provide our managing directors and supervisory directors with directors’ and officers’ liability insurance.

Insofar as indemnification of liabilities arising under the Securities Act may be permitted to supervisory directors, managing directors or persons controlling us pursuant to the foregoing provisions, we have been informed that, in the opinion of the SEC such indemnification is against public policy as expressed in the Securities Act and is therefore unenforceable.

The following table sets forth information relating to the beneficial ownership of our ordinary shares as of March 31, 2013, by:

The number of ordinary shares beneficially owned by each entity, person, director or executive officer is determined in accordance with the rules of the SEC, and the information is not necessarily indicative of beneficial ownership for any other purpose. Under such rules, beneficial ownership includes any shares over which the individual has sole or shared voting power or investment power as well as any shares that the individual has the right to acquire within 60 days of March 31, 2013 through the exercise of any option, warrant or other right. Except as otherwise indicated, and subject to applicable community property laws, the persons named in the table have sole voting and investment power with respect to all ordinary shares held by that person.

The percentage of shares beneficially owned is computed on the basis of 29,002,298 of our ordinary shares as of March 31, 2013, which reflects automatic conversion of all of our outstanding preferred shares into an aggregate of 25,511,240 ordinary shares immediately prior to the consummation of this offering pursuant to the shareholders’ agreement described in “Related party transactions—Shareholders’ agreement.” Ordinary shares that a person has the right to acquire within 60 days of March 31, 2013 are deemed outstanding for purposes of computing the percentage ownership of the person holding such rights, but are not deemed outstanding for purposes of computing the percentage ownership of any other person, except with respect to the percentage ownership of all directors and executive officers as a group. Unless otherwise indicated below, the address for each beneficial owner listed is c/o Prosensa Holding B.V., at J.H. Oortweg 21, 2333 CH Leiden, the Netherlands.

The following is a description of related party transactions we have entered into since January 1, 2010 with any of our members of our supervisory board or management board and the holders of more than 5% of our ordinary shares.

In January 2012, we entered into a subscription agreement pursuant to which we issued and sold an aggregate of 5,000,004 of our Class B2 shares at a price per share of €2.30 for an aggregate purchase price of €11,500,009 and (ii) an aggregate of 4,107,140 of our Class B3 shares at a price per share of €2.80 for an aggregate purchase price of €11,499,992. The following table sets forth the number of our Class B2 and Class B3 shares purchased by our directors, executive officers and 5% shareholders and their affiliates:

On December 8, 2008, all of our then existing shareholders entered into a shareholders agreement, as amended on June 29, 2010 and January 16, 2012 (as amended, the “Shareholders’ Agreement”), the principal terms of which are as follows:

Board composition. Our supervisory board is to consist of one member nominated by each of LSP III Omni, ABV IV Holdings N.V., Idinvest Partners, Gimv N.V. and New Enterprise Associates 13, L.P. (so long as such shareholder’s preferred shares have not been converted to ordinary shares), as well as up to three industry experts nominated by the supervisory board. Martijn Kleijwegt was nominated to our supervisory board by LSP III Omni, Stephen Bunting was nominated to our supervisory board by ABV IV Holdings N.V., Rémi Droller was nominated to our supervisory board by Idinvest Partners, Jim Van heusden was nominated to our supervisory board by Gimv N.V. and David Mott was nominated to our supervisory board by New Enterprise Associates 13, L.P.

Transfer restrictions. Certain transfer restrictions, including a right of first refusal as well as tag-along and drag-along rights by holders of certain of our preferred shares, are provided for.

Anti-dilution/preemptive rights. Holders of Class A and Class B preferred shares have anti-dilution protection in the event we issue shares at a price that is less than the conversion price at which the preferred shares convert into ordinary shares. In the event such shares are issued, Holders of Class A and Class B preferred shares have the option of either (a) adjusting the conversion price at which their preferred shares will convert into ordinary shares to account for the lower price paid by the new shares or (b) causing us to issue to them additional Class A and Class B preferred shares. This right does not apply in the event of a public offering of our shares in connection with which all the outstanding preferred shares are converted into ordinary shares. All existing shareholders also have preemptive rights in the event of any issuance of new shares. These rights are expected to be waived in connection with this offering.

Share conversion. All of the issued preferred shares will convert into our ordinary shares in the event of, among other things, our initial public offering. The conversion rate for the preferred shares is calculated by reference to the original issue price of relevant preferred shares, adjusted for any stock splits, share distributions and, in the case of holders of Class A and Class B preferred shares, certain anti-dilution protections. The conversion rate immediately prior to the consummation of this offering will be one-to-one, and therefore all of our outstanding preferred shares will convert into an aggregate of 25,511,240 ordinary shares. We refer to this as the Share Conversion.

Amendment. The Shareholders’ Agreement may only be amended by the written consent of each of the parties to the agreement.

In connection with the consummation of this offering, the Shareholders’ Agreement will be terminated.

Our Incentive Plans utilize a Dutch foundation called Stichting Administratiekantoor Prosensa Holding (the Foundation). The purpose of the Foundation is to facilitate administration of share-based compensation awards and pool the voting interests of the underlying shares. Upon the exercise of an option right under any of the Incentive Plans, ordinary shares are issued to the Foundation, which thereupon grants a depository receipt for each issued ordinary share to the person exercising its option right. The depositary receipt holder is entitled to any dividends or other distributions paid on the shares for which the depositary receipts are granted. The voting rights attached to the shares are exercised by the Foundation. The depositary receipt holders do not have meeting rights: they are not entitled to attend a general meeting of shareholders or to cast a vote. The voting rights attached to the shares are exercised by the Foundation at its own discretion.

Board members of the Foundation are appointed by our supervisory board. The board consists of at least three board members. Currently, one board member is appointed on the binding nomination of the joint meeting of holders of Class A and Class B preferred shares. A second board member is appointed on the binding nomination of the meeting of holders of ordinary shares. The third board member is an employee.

Effective upon consummation of this offering, we intend to enter into a registration rights agreement with certain of our existing shareholders pursuant to which we will grant them the right, under certain circumstances and subject to certain restrictions, to require us to register under the Securities Act ordinary shares held by them.

We intend to enter into indemnification agreements with our managing directors and supervisory directors. The indemnification agreements and our Articles of Association require us to indemnify our managing directors and supervisory directors to the fullest extent permitted by law. See “Management—Insurance and indemnification” for a description of these indemnification agreements.

Prior to the consummation of this offering, we intend to enter into a related person transaction policy.

We were incorporated on November 26, 1997 as a private company with limited liability (besloten vennootschap met beperkte aansprakelijkheid) under Dutch law. Upon consummation of this offering, we intend to convert into a public company with limited liability (naamloze vennootschap) pursuant to a Deed of Amendment and Conversion, and our legal name will be Prosensa Holding N.V.

We are registered with the Trade Register of the Chamber of Commerce Den Haag, the Netherlands (handelsregister van de Kamer van Koophandel en Fabrieken Den Haag) under number 28076693. Our corporate seat is in Leiden, the Netherlands, and our registered office is J.H. Oortweg 21, 2333 CH Leiden, the Netherlands.

As of the date of this prospectus, our share capital is divided into several series of preferred shares and ordinary shares. All of our outstanding preferred shares will be converted into ordinary shares pursuant to the Share Conversion upon consummation of this offering. Our issued share capital at the date of this prospectus amounts to €290,023.

As of the execution of the Deed of Amendment and Conversion, our authorized share capital will be , divided into ordinary shares, each with a nominal value of € and cumulative preferred shares, each with a nominal value of € . We have adopted an anti-takeover measure pursuant to which our management board may, subject to supervisory board approval but without shareholder approval, issue (or grant the right to acquire) cumulative preferred shares. We may issue an amount of cumulative preferred shares up to 100% of our issued capital immediately prior to the issuance of such preferred shares. In such event, the cumulative preferred shares will be issued to a separate, newly established foundation. If the management board determines to issue the cumulative preferred shares to such a foundation, the foundation’s articles of association will provide that it will act to serve the best interests of us, our associated business and all parties connected to us, by opposing any influences that conflict with these interests and threaten to undermine our continuity, independence and identity. This foundation will be structured to operate independently of us.

The management board may issue these cumulative preferred shares to protect us from influences that do not serve our best interests and threaten to undermine our continuity, independence and identity. These influences may include a third-party acquiring a significant percentage of our ordinary shares, the announcement of a public offer for our ordinary shares, other concentration of control over our ordinary shares or any other form of pressure on us to alter our strategic policies.

Under Dutch law, our authorized share capital is the maximum capital that we may issue without amending our Articles of Association. An amendment of our Articles of Association would

require a resolution of the general meeting of shareholders upon proposal by the management board with the prior approval of the supervisory board.

We intend to apply to list our ordinary shares on Nasdaq under the symbol “RNA.”

Initial settlement of the ordinary shares issued in this offering will take place on the consummation date of this offering through The Depository Trust Company, or DTC, in accordance with its customary settlement procedures for equity securities. Each person owning ordinary shares held through DTC must rely on the procedures thereof and on institutions that have accounts therewith to exercise any rights of a holder of the ordinary shares.

Our Articles of Association as are in force at the date of this prospectus are referred to herein as our “Current Articles.” When we refer to our Articles of Association in this prospectus, we refer to our Articles of Association as they will be in force after the expected execution of the Deed of Amendment and Conversion prior to the consummation of this offering.

Our Current Articles were last amended by deed of amendment, executed on December 18, 2012. We shall further amend our Current Articles and convert our company into a public company with limited liability effective prior to the consummation of this offering. On , 2013, the general meeting of shareholders resolved to amend the Current Articles and to convert into a public company with limited liability (naamloze venootschap), subject to completion of this offering. The draft Deed of Amendment and Conversion was made available to the shareholders prior to the date of such resolution and remains available for inspection by interested parties at our offices in Leiden up to and including the consummation of this offering.

Set forth below is a summary of relevant information concerning our share capital and material provisions of our Articles of Association and applicable Dutch law. This summary does not constitute legal advice regarding those matters and should not be regarded as such.

The general meeting of shareholders may resolve to amend the Articles of Association, at the proposal of the management board, with the prior approval of the supervisory board. A resolution by the general meeting of shareholders to amend the Articles of Association requires a simple majority of the votes cast.

Subject to Dutch law and the Articles of Association, we must keep our shareholders’ register accurate and up-to-date. The management board keeps our shareholders’ register and records names and addresses of all holders of shares, showing the date on which the shares were acquired, the date of the acknowledgement by or notification of us as well as the amount paid on each share. The register also includes the names and addresses of those with a right of use and enjoyment (vruchtgebruik) in shares belonging to another or a pledge in respect of such shares.

Our corporate objectives are: (1) to develop products based on medical bioengineering in the broad sense, in connection with organic chemistry; (2) to incorporate, to participate in, to

conduct the management of and to gain financial or other interest in companies and/or enterprises in other ways; (3) to render administrative, technical, financial, economic or managerial services to other companies, persons and/or enterprises; (4) to acquire, to dispose, to manage and to exploit goods and immovable property including patents, trademark rights, licences, permits and other intellectual property rights; (5) to lend and borrow sums of money and to furnish security for our debts and our subsidiaries’ debts, to warrant performance by or bind ourself jointly or severally or in addition to or on behalf of others, the foregoing independent or in cooperation with third-parties and including the performance and support of everything which in the broadest sense is connected directly or indirectly with the above-mentioned objects.

Under Dutch law, managing directors, supervisory directors and certain other officers may be held liable for damages in the event of improper or negligent performance of their duties. They may be held jointly and severally liable for damages to the Company and to third parties for infringement of the Articles of Association or of certain provisions of the Dutch Civil Code. In certain circumstances, they may also incur additional specific civil and criminal liabilities. Managing directors, supervisory directors and certain other officers are insured under an insurance policy taken out by us against damages resulting from their conduct when acting in the capacities as such directors or officers. In addition, our Articles of Association provide for indemnification of our managing directors and supervisory directors, including reimbursement for reasonable legal fees and damages or fines based on acts or failures to act in their duties. Such indemnification will not be available in instances of willful (opzettelijk), intentionally reckless (bewust roekeloos) or seriously culpable (ernstig verwijtbaar) conduct unless Dutch law provides otherwise for additional information, please see “Management—Insurance and indemnification.”

General meetings of shareholders are held in Leiden, Amsterdam or in the municipality of Haarlemmermeer (Schiphol Airport), the Netherlands. The annual general meeting of shareholders must be held within six months of the end of each financial year. Additional extraordinary general meetings of shareholders may also be held, whenever considered appropriate by the management board or the supervisory board. Pursuant to Dutch law, one or more shareholders, who jointly represent at least one-tenth of the issued capital may, on their application, be authorized by Court to convene a general meeting of shareholders. The Court shall disallow the application if it does not appear that the applicants have previously requested the management board and the supervisory board to convene a general meeting of shareholders and neither the management nor the supervisory board has taken the necessary steps so that the general meeting of shareholders could be held within six weeks after the request.

General meetings of shareholders shall be convened by a notice, which shall include an agenda stating the items to be discussed, including for the annual general meeting of shareholders, among other things, the adoption of the annual accounts, appropriation of our profits and proposals relating to the composition of the management board or supervisory board, including the filling of any vacancies in the management board or supervisory board. In addition, the agenda shall include such items as have been included therein by the management board or

supervisory board. The agenda shall also include such items requested by one or more shareholders, and others entitled to attend general meetings of shareholders, representing at least 1% of the issued share capital or representing a value of at least €50 million. Under recently adopted legislation, the 1% threshold will be increased to 3% with effect as of July 1, 2013, except where the Articles of Association state a lower percentage, and the €50 million threshold will cease to apply. Our Articles of Association do not state such lower percentage. Requests must be made in writing and received by the management board at least sixty days before the day of the convocation of the meeting. The management board may decide not to place items so requested on the agenda, if they are of the opinion that doing so would be detrimental to our vital interests. No resolutions shall be adopted on items other than those which have been included in the agenda.

The general meeting is presided over by the chairman of the supervisory board. However, the chairman may charge another person to preside over the general meeting in his place even if he himself is present at the meeting. If the chairman of the supervisory board is absent and he has not charged another person to preside over the meeting in his place, the supervisory directors present at the meeting shall appoint one of them to be chairman. If no members of the supervisory board are present at the general meeting, the general meeting is to be presided over by the chairman of the management board or, if the chairman of the management board is absent, by one of the other managing directors designated for that purpose by the management board. Managing directors and supervisory directors may attend a general meeting of shareholders. In these meetings, they have an advisory vote. The chairman of the meeting may decide at its discretion to admit other persons to the meeting.

All shareholders and others entitled to attend general meetings of shareholders are authorized to attend the general meeting of shareholders, to address the meeting and, in so far as they have such right, to vote.

Each ordinary share confers the right on the holder to cast one vote at the general meeting of shareholders. Shareholders may vote by proxy. The voting rights attached to any shares held by us are suspended as long as they are held in treasury. Nonetheless, the holders of a right of use and enjoyment (vruchtgebruik) in shares belonging to another and the holders of a right of pledge in respect of ordinary shares held by us are not excluded from any right they may have to vote on such ordinary shares, if the right of use and enjoyment (vruchtgebruik) or the right of pledge was granted prior to the time such ordinary share was acquired by us. We may not cast votes in respect of a share in respect of which there is a right of use and enjoyment (vruchtgebruik) or a right of pledge. Shares which are not entitled to voting rights pursuant to the preceding sentences will not be taken into account for the purpose of determining the number of shareholders that vote and that are present or represented, or the amount of the share capital that is provided or that is represented at a general meeting of shareholders.

In accordance with Dutch law and generally accepted business practices, our articles of association do not provide quorum requirements generally applicable to general meetings of shareholders. To this extent, our practice varies from the requirement of Nasdaq Listing Rule 5620(c), which requires an issuer to provide in its bylaws for a generally applicable quorum, and that such quorum may not be less than one-third of the outstanding voting stock.

Decisions of the general meeting of shareholders are taken by an absolute majority of votes cast, except where Dutch law or the Articles of Association provide for a qualified majority or unanimity.

Under our Articles of Association, the managing directors and supervisory directors are appointed by the general meeting of shareholders upon nomination by our supervisory board. However, the general meeting of shareholders may at all times overrule the binding nomination by a resolution adopted by at least a two-thirds majority of the votes cast, provided such majority represents more than half of the issued share capital. If the general meeting of shareholders overrules the binding nomination, the supervisory board shall make a new nomination.

Under Dutch law, the management board is responsible for our management, strategy, policy and operations. The supervisory board is responsible for supervising the conduct of and providing advice to the management board and for supervising our business generally. Furthermore, each managing director and supervisory director has a duty to act in the corporate interest of the company. Under Dutch law, the corporate interest extends to the interests of all corporate stakeholders, such as shareholders, creditors, employees, customers and suppliers. The duty to act in the corporate interest of the company also applies in the event of a proposed sale or break-up of the company, whereby the circumstances generally dictate how such duty is to be applied. Any resolution of the management board regarding a significant change in our identity or character requires shareholder approval.

We may only make distributions to our shareholders if our shareholders’ equity exceeds the sum of the paid-in and called-up share capital plus the reserves as required to be maintained by Dutch law or by the Articles of Association. Under the Articles of Association, a dividend is first paid out of the profit, if available for distribution, on any preferred shares, of which none will be outstanding after the Share Conversion prior to the consummation of this offering. Any amount remaining out of the profit is carried to reserve as the management board determines, subject to the approval of the supervisory board. After reservation by the management board of any profit, the remaining profit will be at the disposal of the general meeting of shareholders.

We only make a distribution of dividends to our shareholders after the adoption of our annual accounts demonstrating that such distribution is legally permitted. The management board is permitted, subject to certain requirements and subject to approval of the supervisory board, to declare interim dividends without the approval of the general meeting of shareholders.

Dividends and other distributions shall be made payable not later than the date determined by the management board. Claims to dividends and other distributions not made within five years from the date that such dividends or distributions became payable, will lapse and any such amounts will be considered to have been forfeited to us (verjaring).

Under existing laws of the Netherlands, there are no exchange controls applicable to the transfer to persons outside of the Netherlands of dividends or other distributions with respect to, or of the proceeds from the sale of, shares of a Dutch company.

Pursuant to Section 92a, Book 2, Dutch Civil Code, a shareholder who for his own account contributes at least 95% of our issued share capital may initiate proceedings against our minority shareholders jointly for the transfer of their shares to the claimant. The proceedings are held before the Enterprise Chamber and can be instituted by means of a writ of summons served upon each of the minority shareholders in accordance with the provisions of the Dutch Code of Civil Procedure (Wetboek van Burgerlijke Rechtsvordering). The Enterprise Chamber may grant the claim for squeeze out in relation to all minority shareholders and will determine the price to be paid for the shares, if necessary after appointment of one or three experts who will offer an opinion to the Enterprise Chamber on the value to be paid for the shares of the minority shareholders. Once the order to transfer becomes final before the Enterprise Chamber, the person acquiring the shares shall give written notice of the date and place of payment and the price to the holders of the shares to be acquired whose addresses are known to him. Unless the addresses of all of them are known to the acquiring person, such person is required to publish the same in a daily newspaper with a national circulation.

Pursuant to the Dutch Financial Markets Supervision Act (Wet op het financieel toezicht, “FMSA”), any managing director or supervisory director and any other person who has managerial or co-managerial responsibilities in respect of us or who has the authority to make decisions affecting our future developments and business prospects and who may have regularly access to inside information relating, directly or indirectly, to us, must give written notice to the Netherlands Authority for the Financial Markets (NAFM) by means of a standard form of any transactions conducted for his own account relating to our shares or in financial instruments the value of which is also based on the value of our shares.

Furthermore, in accordance with the FMSA and the regulations promulgated thereunder, certain persons who are closely associated with members of our supervisory board or any of the other persons as described above, are required to notify the NAFM of any transactions conducted for their own account relating to our shares or in financial instruments the value of which is also based on the value of our shares. The FMSA and the regulations promulgated thereunder cover the following categories of persons: (1) the spouse or any partner considered by national law as equivalent to the spouse, (2) dependent children, (3) other relatives who have shared the same household for at least one year at the relevant transaction date, and (4) any legal person, trust or partnership whose, among other things, managerial responsibilities are discharged by a person referred to under (1), (2) or (3) above or by the relevant supervisory director or other person with any authority in respect of us as described above.

The NAFM must be notified no later than the fifth business day following the relevant transaction date. Under certain circumstances, notification may be postponed until the date the value of the transactions performed for that person’s own account, together with transactions

carried out by the persons closely associated with that person, amounts to €5,000 or more in the calendar year in question.

Non-compliance with the notification obligations under the FMSA could lead to criminal fines, administrative fines, imprisonment or other sanctions. In addition, non-compliance with some of the notification obligations under the FMSA may lead to civil sanctions, including suspension of the voting rights relating to our shares held by the offender for a period of not more than three years and a prohibition to own shares or voting rights on our shares for a period of not more than five years.

The NAFM does not issue separate public announcements of notifications received by it. It does, however, keep a public register of all notifications under the FMSA on its website, http://www.afm.nl. Third parties can request to be notified automatically by e-mail of changes to the public register in relation to a particular company’s shares or a particular notifying party.

The FMSA contains rules intended to prevent market abuse, such as insider trading, tipping and market manipulation.

Pursuant to the rules intended to prevent market abuse, prior to the consummation of this offering we intend to adopt an internal code on inside information in respect of the holding of and carrying out of transactions by managing directors, supervisory directors and employees in our shares or in financial instruments the value of which is determined by the value of our shares. Furthermore, we have drawn up a list of those persons working for us who could have access to inside information on a regular or incidental basis and have informed such persons of the rules on insider trading and market manipulation, including the sanctions which can be imposed in the event of a violation of those rules.

Comparison of Dutch corporate law and our Articles of Association and U.S. corporate law

The following comparison between Dutch corporation law, which applies to us, and Delaware corporation law, the law under which many publicly listed corporations in the United States are incorporated, discusses additional matters not otherwise described in this prospectus. Although we believe this summary is materially accurate, the summary is subject to Dutch law, including Book 2 of the Dutch Civil Code and Delaware corporation law, including the Delaware General Corporation Law.

The Netherlands. We have a two-tier board structure consisting of our management board (raad van bestuur) and a separate supervisory board (raad van commissarissen).

Under Dutch law, the management board is responsible for the management and the strategy, policy and operations of the company. The supervisory board is responsible for supervising the conduct of and providing advice to the management board and for supervising the business generally. Furthermore, each managing director and supervisory director has a duty to act in the corporate interest of the company. Under Dutch law, the corporate interest extends to the interests of all corporate stakeholders, such as shareholders, creditors, employees, customers and suppliers. The duty to act in the corporate interest of the company also applies in the event of a

proposed sale or break-up of the company, whereby the circumstances generally dictate how such duty is to be applied. Any resolution of the management board regarding a significant change in the identity or character of the company requires shareholders’ approval.

Delaware. The board of directors bears the ultimate responsibility for managing the business and affairs of a corporation. In discharging this function, directors of a Delaware corporation owe fiduciary duties of care and loyalty to the corporation and to its stockholders. Delaware courts have decided that the directors of a Delaware corporation are required to exercise informed business judgment in the performance of their duties. Informed business judgment means that the directors have informed themselves of all material information reasonably available to them. Delaware courts have also imposed a heightened standard of conduct upon directors of a Delaware corporation who take any action designed to defeat a threatened change in control of the corporation. In addition, under Delaware law, when the board of directors of a Delaware corporation approves the sale or break-up of a corporation, the board of directors may, in certain circumstances, have a duty to obtain the highest value reasonably available to the stockholders.

The Netherlands. Under Dutch law, managing directors of a listed company are generally appointed for an individual term of a maximum of four years. There is no limit in the number of consecutive terms managing directors may serve. Our managing directors are appointed by the general meeting of shareholders for a term of up to four years. A managing director can be reappointed for a new term of up to four years.

The general meeting of shareholders shall at all times be entitled to suspend or dismiss a managing director. The general meeting of shareholders may only adopt a resolution to suspend or dismiss such managing director by at least a two thirds majority of the votes cast, if such majority represents more than half of the issued share capital, unless the proposal was made by the supervisory board, in which case a simple majority of the votes cast is sufficient. The supervisory board may at all times suspend (but not dismiss) a managing director.

Delaware. The Delaware General Corporation Law generally provides for a one-year term for directors, but permits directorships to be divided into up to three classes with up to three-year terms, with the years for each class expiring in different years, if permitted by the certificate of incorporation, an initial bylaw or a bylaw adopted by the stockholders. A director elected to serve a term on a “classified” board may not be removed by stockholders without cause. There is no limit in the number of terms a director may serve.

The Netherlands. Under Dutch law, new managing directors are appointed by the general meeting of shareholders. Under our Articles of Association, managing directors are appointed by the general meeting of shareholders upon the binding nomination by our supervisory board. However, the general meeting of shareholders may at all times overrule the binding nomination by a resolution adopted by at least a two-thirds majority of the votes cast, provided such majority represents more than half of the issued share capital. If the general meeting of shareholders overrules the binding nomination, the supervisory board shall make a new nomination.

Delaware. The Delaware General Corporation Law provides that vacancies and newly created directorships may be filled by a majority of the directors then in office (even though less than a

quorum) unless (i) otherwise provided in the certificate of incorporation or bylaws of the corporation or (ii) the certificate of incorporation directs that a particular class of stock is to elect such director, in which case any other directors elected by such class, or a sole remaining director elected by such class, will fill such vacancy.

The Netherlands. Under our Articles of Association, managing directors and supervisory directors shall not take part in any discussion or decision-making that involves a subject or transaction in relation to which he or she has a conflict of interest with us. Our Articles of Association provide that if as a result thereof no resolution of the management board can be adopted, the resolution is adopted by the supervisory board. If as a result of the conflict of interest of supervisory directors no resolution of the supervisory board can be adopted, the resolution can nonetheless be adopted by the supervisory board. In that case, each supervisory board member is entitled to participate in the discussion and decision making process and to cast a vote.

Delaware. The Delaware General Corporation Law generally permits transactions involving a Delaware corporation and an interested director of that corporation if:

The Netherlands. An absent managing director may issue a proxy for a specific management board meeting but only to another management board member in writing. An absent supervisory director may issue a proxy for a specific supervisory board meeting but only to another supervisory board member in writing.

Delaware. A director of a Delaware corporation may not issue a proxy representing the director’s voting rights as a director.

The Netherlands. In accordance with Dutch law and our Articles of Association, each issued ordinary share confers the right to cast one vote at the general meeting of shareholders. Each holder of ordinary shares may cast as many votes as it holds shares. Shares that are held by us or our direct or indirect subsidiaries do not confer the right to vote.

For each general meeting of shareholders, a record date will be applied with respect to ordinary shares in order to establish which shareholders are entitled to attend and vote at the general meeting of shareholders, which date is set by the management board. The record date and the manner in which shareholders can register and exercise their rights will be set out in the notice of the meeting.

Delaware. Under the Delaware General Corporation Law, each stockholder is entitled to one vote per share of stock, unless the certificate of incorporation provides otherwise. In addition, the certificate of incorporation may provide for cumulative voting at all elections of directors of the corporation, or at elections held under specified circumstances. Either the certificate of incorporation or the bylaws may specify the number of shares and/or the amount of other securities that must be represented at a meeting in order to constitute a quorum, but in no event will a quorum consist of less than one third of the shares entitled to vote at a meeting.

Stockholders as of the record date for the meeting are entitled to vote at the meeting, and the board of directors may fix a record date that is no more than 60 nor less than 10 days before the date of the meeting, and if no record date is set then the record date is the close of business on the day next preceding the day on which notice is given, or if notice is waived then the record date is the close of business on the day next preceding the day on which the meeting is held. The determination of the stockholders of record entitled to notice or to vote at a meeting of stockholders shall apply to any adjournment of the meeting, but the board of directors may fix a new record date for the adjourned meeting.

The Netherlands. Pursuant to our Articles of Association, extraordinary general meetings of shareholders will be held whenever our supervisory board or management board deems such to be necessary. Pursuant to Dutch law, one or more shareholders representing at least one-tenth of the issued share capital may request the Dutch courts to order that a general meeting of shareholders be held and may, on their application, be authorized by the court to convene a general meeting of shareholders. The court shall disallow the application if it does not appear that the applicants have previously requested the management board and the supervisory board to convene a general meeting of shareholders and neither the management nor the supervisory board has taken the necessary steps so that the general meeting of shareholders could be held within six weeks after the request.

Also, the agenda for a general meeting of shareholders shall include such items requested by one or more shareholders, and others entitled to attend general meetings of shareholders, representing at least 1% of the issued share capital or representing a value of at least € 50 million. Under recently adopted legislation, the 1% threshold will be increased to 3% with effect as of July 1, 2013, except where the Articles of Association state a lower percentage, and the €50 million threshold will cease to apply. The Articles of Association do not state such lower percentage.

Delaware. Delaware law does not specifically grant stockholders the right to bring business before an annual or special meeting. However, if a Delaware corporation is subject to the SEC’s proxy rules, a stockholder who owns at least $2,000 in market value, or 1% of the corporation’s securities entitled to vote, may propose a matter for a vote at an annual or special meeting in accordance with those rules.

The Netherlands. Under Dutch law, shareholders’ resolutions may be adopted in writing without holding a meeting of shareholders, provided that (i) all shareholders agree on this practice for decision making and, (ii) the resolution is adopted unanimously by all shareholders

that are entitled to vote. For a listed company, this method of adopting resolutions is not feasible.

Delaware. Although permitted by Delaware law, publicly listed companies do not typically permit stockholders of a corporation to take action by written consent.

The Netherlands. The concept of appraisal rights is not known as such under Dutch law.

However, pursuant to Dutch law a shareholder who for his own account contributes at least 95% of our issued share capital may initiate proceedings against our minority shareholders jointly for the transfer of their shares to the claimant. The proceedings are held before the Enterprise Chamber. The Enterprise Chamber may grant the claim for squeeze out in relation to all minority shareholders and will determine the price to be paid for the shares, if necessary after appointment of one or three experts who will offer an opinion to the Enterprise Chamber on the value to be paid for the shares of the minority shareholders. Once the order to transfer becomes final before the Enterprise Chamber, the person acquiring the shares shall give written notice of the date and place of payment and the price to the holders of the shares to be acquired whose addresses are known to him. Unless the addresses of all of them are known to the acquiring person, such person is required to publish the same in a daily newspaper with a national circulation.

Furthermore, in accordance with the directive 2005/56/EC of the European Parliament and the Council of October 26, 2005 on cross-border mergers of limited liability companies, Dutch law provides that, to the extent that the acquiring company in a cross-border merger is organized under the laws of another EU member state, a shareholder of a Dutch disappearing company who has voted against the cross-border merger may file a claim with the Dutch company for compensation. Such compensation to be determined by one or more independent experts. The shares of such shareholder that are subject to such claim will cease to exist as of the moment of entry into effect of the cross-border merger.

Payment by the acquiring company is only possible if the resolution to approve the cross-border merger by the corporate body of the other company or companies involved in the cross-border merger includes the acceptance of the rights of the shareholders of the Dutch company to oppose the cross-border merger.

Delaware. The Delaware General Corporation Law provides for stockholder appraisal rights, or the right to demand payment in cash of the judicially determined fair value of the stockholder’s shares, in connection with certain mergers and consolidations.

The Netherlands. In the event a third party is liable to a Dutch company, only the company itself can bring a civil action against that party. The individual shareholders do not have the right to bring an action on behalf of the company. Only in the event that the cause for the liability of a third party to the company also constitutes a tortious act directly against a shareholder does that shareholder have an individual right of action against such third party in its own name. The Dutch Civil Code provides for the possibility to initiate such actions collectively. A foundation or an association whose objective is to protect the rights of a group of persons having similar

interests can institute a collective action. The collective action itself cannot result in an order for payment of monetary damages but may only result in a declaratory judgment (verklaring voor recht). In order to obtain compensation for damages, the foundation or association and the defendant may reach—often on the basis of such declaratory judgment—a settlement. A Dutch court may declare the settlement agreement binding upon all the injured parties with an opt-out choice for an individual injured party. An individual injured party may also itself institute a civil claim for damages.

Delaware. Under the Delaware General Corporation Law, a stockholder may bring a derivative action on behalf of the corporation to enforce the rights of the corporation. An individual also may commence a class action suit on behalf of himself and other similarly situated stockholders where the requirements for maintaining a class action under Delaware law have been met. A person may institute and maintain such a suit only if that person was a stockholder at the time of the transaction which is the subject of the suit. In addition, under Delaware case law, the plaintiff normally must be a stockholder at the time of the transaction that is the subject of the suit and throughout the duration of the derivative suit. Delaware law also requires that the derivative plaintiff make a demand on the directors of the corporation to assert the corporate claim before the suit may be prosecuted by the derivative plaintiff in court, unless such a demand would be futile.

The Netherlands. Under Dutch law, a company such as ours may not subscribe for newly issued shares in its own capital. Such company may, however, subject to certain restrictions of Dutch law and its Articles of Association, acquire shares in its own capital. We may acquire fully paid shares in our own capital at any time for no valuable consideration. Furthermore, subject to certain provisions of Dutch law and our Articles of Association, we may repurchase fully paid shares in our own capital if (i) such repurchase would not cause our shareholders’ equity to fall below an amount equal to the sum of the paid-up and called-up part of the issued share capital and the reserves we are required to maintain pursuant to applicable law and (ii) we would not as a result of such repurchase hold more than 50% of our own issued share capital.

Other than shares acquired for no valuable consideration, ordinary shares may only be acquired following a resolution of our management board, acting pursuant to an authorization for the repurchase of shares granted by the general meeting of shareholders. An authorization by the general meeting of shareholders for the repurchase of shares can be granted for a maximum period of 18 months. Such authorization must specify the number and class of shares that may be acquired, the manner in which these shares may be acquired and the price range within which the shares may be acquired. Our management board has been authorized, acting with the approval of our supervisory board, for a period of 18 months to cause the repurchase of ordinary shares by us of up to 50% of our issued share capital, for a price per share not exceeding 110% of the average closing price of the ordinary shares on the Nasdaq Global Market for the five trading days prior to the day of purchase.

No authorization of the general meeting of shareholders is required if ordinary shares are acquired by us with the intention of transferring such ordinary shares to our employees under an applicable employee stock purchase plan.

Delaware. Under the Delaware General Corporation Law, a corporation may purchase or redeem its own shares unless the capital of the corporation is impaired or the purchase or redemption

would cause an impairment of the capital of the corporation. A Delaware corporation may, however, purchase or redeem out of capital any of its preferred shares or, if no preferred shares are outstanding, any of its own shares if such shares will be retired upon acquisition and the capital of the corporation will be reduced in accordance with specified limitations.

The Netherlands. Under Dutch law, various protective measures are possible and permissible within the boundaries set by Dutch law and Dutch case law. We have adopted several provisions that may have the effect of making a takeover of our company more difficult or less attractive, including:

Delaware. In addition to other aspects of Delaware law governing fiduciary duties of directors during a potential takeover, the Delaware General Corporation Law also contains a business combination statute that protects Delaware companies from hostile takeovers and from actions following the takeover by prohibiting some transactions once an acquirer has gained a significant holding in the corporation.

Section 203 of the Delaware General Corporation Law prohibits “business combinations,” including mergers, sales and leases of assets, issuances of securities and similar transactions by a corporation or a subsidiary with an interested stockholder that beneficially owns 15% or more of a corporation’s voting stock, within three years after the person becomes an interested stockholder, unless:

A Delaware corporation may elect not to be governed by Section 203 by a provision contained in the original certificate of incorporation of the corporation or an amendment to the original certificate of incorporation or to the bylaws of the company, which amendment must be approved by a majority of the shares entitled to vote and may not be further amended by the board of directors of the corporation. Such an amendment is not effective until twelve months following its adoption.

The Netherlands. The management board and the supervisory board provide the general meeting of shareholders in good time with all information that the shareholders require for the exercise of their powers, unless this would be contrary to an overriding interest of us. If the management board or supervisory board invokes an overriding interest, it must give reasons.

Delaware. Under the Delaware General Corporation Law, any stockholder may inspect for any proper purpose certain of the corporation’s books and records during the corporation’s usual hours of business.

The Netherlands. Under our Articles of Association, the general meeting of shareholders shall at all times be entitled to suspend or dismiss a managing director or supervisory director. The general meeting of shareholders may only adopt a resolution to suspend or dismiss such a member by at least a two thirds majority of the votes cast, provided such majority represents more than half of the issued share capital, unless the proposal was made by the supervisory board in which case a simple majority of the votes cast is sufficient.

Delaware. Under the Delaware General Corporation Law, any director or the entire board of directors may be removed, with or without cause, by the holders of a majority of the shares then entitled to vote at an election of directors, except (i) unless the certificate of incorporation provides otherwise, in the case of a corporation whose board is classified, stockholders may effect such removal only for cause, or (ii) in the case of a corporation having cumulative voting, if less than the entire board is to be removed, no director may be removed without cause if the votes cast against his removal would be sufficient to elect him if then cumulatively voted at an election of the entire board of directors, or, if there are classes of directors, at an election of the class of directors of which he is a part.

The Netherlands. Under Dutch law, in the event of an issuance of ordinary shares, each shareholder will have a pro rata preemptive right in proportion to the aggregate nominal value of the ordinary shares held by such holder (with the exception of ordinary shares to be issued to employees or ordinary shares issued against a contribution other than in cash). Under our Articles of Association, the preemptive rights in respect of newly issued ordinary shares may be restricted or excluded by a resolution of the general meeting of shareholders upon proposal of the management board.

The management board, subject to approval of the supervisory board, may restrict or exclude the preemptive rights in respect of newly issued ordinary shares if it has been designated as the authorized body to do so by the general meeting of shareholders. Such designation can be

granted for a period not exceeding five years. A resolution of the general meeting of shareholders to restrict or exclude the preemptive rights or to designate the management board as the authorized body to do so requires a two-thirds majority of the votes cast, if less than one half of our issued share capital is represented at the meeting.

At our annual general meeting held on , 2013 the general meeting of shareholders authorized our management board acting with the approval of our supervisory board for a period of five years from , 2013 to limit or exclude preemptive rights accruing to shareholders in connection with the issue of ordinary shares or rights to subscribe for ordinary shares.

Delaware. Under the Delaware General Corporation Law, stockholders have no preemptive rights to subscribe for additional issues of stock or to any security convertible into such stock unless, and to the extent that, such rights are expressly provided for in the certificate of incorporation.

The Netherlands. Dutch law provides that dividends may be distributed after adoption of the annual accounts by the general meeting of shareholders from which it appears that such dividend distribution is allowed. Moreover, dividends may be distributed only to the extent the shareholders’ equity exceeds the amount of the paid-up and called-up part of the issued share capital and the reserves that must be maintained under the law or the Articles of Association. Interim dividends may be declared as provided in the Articles of Association and may be distributed to the extent that the shareholders’ equity exceeds the amount of the issued and paid-up and called-up part of the issued share capital and the required legal reserves as described above as apparent from our financial statements. Under Dutch law, the Articles of Association may prescribe that the management board decide what portion of the profits are to be held as reserves.

Under the Articles of Association first a dividend is paid out of the profit, if available for distribution, on any preferred shares, of which none will be outstanding after the Share Conversion upon consummation of this offering. Any amount remaining out of the profit is carried to reserve as the management board determines, subject to the approval of the supervisory board. After reservation by the management board of any profit, the remaining profit will be at the disposal of the general meeting of shareholders. We only make a distribution of dividends to our shareholders after the adoption of our annual accounts demonstrating that such distribution is legally permitted. The management board is permitted, subject to certain requirements and subject to approval of the supervisory board, to declare interim dividends without the approval of the general meeting of shareholders.

Dividends and other distributions shall be made payable not later than the date determined by the management board. Claims to dividends and other distribution not made within five years from the date that such dividends or distributions became payable, will lapse and any such amounts will be considered to have been forfeited to us (verjaring).

Delaware. Under the Delaware General Corporation Law, a Delaware corporation may pay dividends out of its surplus (the excess of net assets over capital), or in case there is no surplus, out of its net profits for the fiscal year in which the dividend is declared and/or the preceding

fiscal year (provided that the amount of the capital of the corporation is not less than the aggregate amount of the capital represented by the issued and outstanding stock of all classes having a preference upon the distribution of assets). In determining the amount of surplus of a Delaware corporation, the assets of the corporation, including stock of subsidiaries owned by the corporation, must be valued at their fair market value as determined by the board of directors, without regard to their historical book value. Dividends may be paid in the form of common stock, property or cash.

The Netherlands. Under Dutch law, the general meeting of shareholders must approve resolutions of the management board relating to a significant change in the identity or the character of the company or the business of the company, which includes:

Under Dutch law, a shareholder who owns shares representing at least 95% of the nominal value of a company’s issued share capital may institute proceedings against the company’s other shareholders jointly for the transfer of their shares to that shareholder. The proceedings are held before the Enterprise Chamber (Ondernemingskamer), which may grant the claim for squeeze-out in relation to all minority shareholders and will determine the price to be paid for the shares, if necessary after appointment of experts who will offer an opinion to the Enterprise Chamber on the value of the shares.

Delaware. Under the Delaware General Corporation Law, the vote of a majority of the outstanding shares of capital stock entitled to vote thereon generally is necessary to approve a merger or consolidation or the sale of all or substantially all of the assets of a corporation. The Delaware General Corporation Law permits a corporation to include in its certificate of incorporation a provision requiring for any corporate action the vote of a larger portion of the stock or of any class or series of stock than would otherwise be required.

Under the Delaware General Corporation Law, no vote of the stockholders of a surviving corporation to a merger is needed, however, unless required by the certificate of incorporation, if (i) the agreement of merger does not amend in any respect the certificate of incorporation of the surviving corporation, (ii) the shares of stock of the surviving corporation are not changed in the merger and (iii) the number of shares of common stock of the surviving corporation into which any other shares, securities or obligations to be issued in the merger may be converted does not exceed 20% of the surviving corporation’s common stock outstanding immediately prior to the effective date of the merger. In addition, stockholders may not be entitled to vote in

certain mergers with other corporations that own 90% or more of the outstanding shares of each class of stock of such corporation, but the stockholders will be entitled to appraisal rights.

The Netherlands. Under Dutch law and our Articles of Association, we must adopt a remuneration policy for managing directors. Such remuneration policy shall be adopted by the general meeting of shareholders upon the proposal of the supervisory board. The supervisory board determines the remuneration of the managing directors in accordance with the remuneration policy. A proposal by the supervisory board with respect to remuneration schemes in the form of shares or rights to shares is submitted by the supervisory board to the general meeting for its approval. This proposal must set out at least the maximum number of shares or rights to shares to be granted to the management board and the criteria for granting or amendment.

The general meeting may determine the remuneration of supervisory directors. The supervisory directors shall be reimbursed for their expenses.

Delaware. Under the Delaware General Corporation Law, the stockholders do not generally have the right to approve the compensation policy for directors or the senior management of the corporation, although certain aspects of executive compensation may be subject to stockholder vote due to the provisions of U.S. federal securities and tax law, as well as exchange requirements.

Prior to this offering, there has been no market for our ordinary shares. Future sales of substantial amounts of our ordinary shares in the public market could adversely affect market prices prevailing from time to time. Furthermore, because only a limited number of ordinary shares will be available for sale shortly after this offering due to existing contractual and legal restrictions on resale as described below, there may be sales of substantial amounts of our ordinary shares in the public market after such restrictions lapse. This may adversely affect the prevailing market price of our ordinary shares and our ability to raise equity capital in the future.

Upon completion of this offering, we will have ordinary shares outstanding, or ordinary shares outstanding if the underwriters exercise their option in full to purchase additional ordinary shares, and assuming the conversion of all outstanding preferred shares pursuant to the Share Conversion. Of these shares, ordinary shares, or ordinary shares if the underwriters exercise their option in full to purchase additional shares, sold in this offering will be freely transferable without restriction or registration under the Securities Act, except for any shares purchased by one of our existing “affiliates,” as that term is defined in Rule 144 under the Securities Act. The remaining ordinary shares are “restricted shares” as defined in Rule 144. Restricted shares may be sold in the public market only if registered or if they qualify for an exemption from registration under Rules 144 or 701 of the Securities Act. As a result of the contractual 180-day lock-up period described below and the provisions of Rules 144 and 701, these shares will be available for sale in the public market as follows:

In general, a person who has beneficially owned our ordinary shares that are restricted shares for at least six months would be entitled to sell such securities, provided that (i) such person is not deemed to have been one of our affiliates at the time of, or at any time during the 90 days preceding, a sale and (ii) we are subject to the Exchange Act periodic reporting requirements for at least 90 days before the sale. Persons who have beneficially owned our ordinary shares that are restricted shares for at least six months but who are our affiliates at the time of, or any time during the 90 days preceding, a sale, would be subject to additional restrictions, by which such person would be entitled to sell within any three month period only a number of securities that does not exceed the greater of either of the following:

provided, in each case, that we are subject to the Exchange Act periodic reporting requirements for at least 90 days before the sale. Such sales both by affiliates and by non-affiliates must also comply with the manner of sale, current public information and notice provisions of Rule 144 to the extent applicable.

In general, under Rule 701, any of our employees, directors, officers, consultants or advisors who purchases shares from us in connection with a compensatory share or option plan or other written agreement before the effective date of this offering is entitled to resell such shares 90 days after the effective date of this offering in reliance on Rule 144, without having to comply with the holding period requirements or other restrictions contained in Rule 701.

The SEC has indicated that Rule 701 will apply to typical share options granted by an issuer before it becomes subject to the reporting requirements of the Exchange Act, along with the shares acquired upon exercise of such options, including exercises after the date of this prospectus. Securities issued in reliance on Rule 701 are restricted securities and, subject to the contractual restrictions described below, beginning 90 days after the date of this prospectus, may be sold by persons other than “affiliates,” as defined in Rule 144, subject only to the manner of sale provisions of Rule 144 and by “affiliates” under Rule 144 without compliance with its one-year minimum holding period requirement.

Regulation S provides generally that sales made in offshore transactions are not subject to the registration or prospectus-delivery requirements of the Securities Act.

We intend to enter into a registration rights agreement upon consummation of this offering pursuant to which we will agree under certain circumstances to file a registration statement to register the resale of the shares held by certain of our existing shareholders, as well as to cooperate in certain public offerings of such shares. Registration of these shares under the Securities Act would result in these shares becoming freely tradable without restriction under the Securities Act immediately upon the effectiveness of the registration, except for shares purchased by affiliates. See “Related party transactions—Registration rights agreement.”

All of our directors, executive officers and the holders of approximately of our ordinary shares have agreed, subject to limited exceptions, not to offer, pledge, announce the intention to sell, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase or otherwise dispose of, directly or indirectly, or enter into any swap or other agreement that transfers, in whole or in part, any of the economic consequences of ownership of the ordinary shares or such other securities for a period of 180 days after the date of this prospectus, subject to certain exceptions, without the prior written consent of J.P. Morgan Securities LLC. See “Underwriting.”

The following summary contains a description of certain Dutch and U.S. federal income tax consequences of the acquisition, ownership and disposition of ordinary shares, but it does not purport to be a comprehensive description of all the tax considerations that may be relevant to a decision to purchase ordinary shares. The summary is based upon the tax laws of Dutch and regulations thereunder and on the tax laws of the United States and regulations thereunder as of the date hereof, which are subject to change.

The following discussion is a summary of the material Dutch tax considerations relating to the purchase, ownership and disposition of our ordinary shares.

The following is intended as general information only and it does not purport to present any comprehensive or complete description of all aspects of Dutch tax law which could be of relevance to a holder of ordinary shares (a “Shareholder”). For Dutch tax purposes, a Shareholder may include an individual or entity who does not have the legal title of the shares, but to whom nevertheless the shares are attributed based either on such individual or entity holding a beneficial interest in the shares or based on specific statutory provisions, including statutory provisions pursuant to which shares are attributed to an individual who is, or who has directly or indirectly inherited from a person who was, the settlor, grantor or similar originator of a trust, foundation or similar entity that holds the shares.

Prospective Shareholders should therefore consult their tax adviser regarding the tax consequences of any purchase, ownership or disposal of ordinary shares.

The following summary is based on the Dutch tax law as applied and interpreted by Dutch tax courts and as published and in effect on the date hereof, without prejudice to any amendments introduced at a later date and implemented with or without retroactive effect.

For the purpose of this paragraph, “Dutch Taxes” shall mean taxes of whatever nature levied by or on behalf of the Netherlands or any of its subdivisions or taxing authorities. The Netherlands means the part of the Kingdom of the Netherlands located in Europe.

A Shareholder is generally subject to Dutch dividend withholding tax at a rate of 15% on dividends distributed by the company. Generally, the company is responsible for the withholding of such dividend withholding tax at source; the dividend withholding tax is for the account of the Shareholder.

(a) the general meeting of Shareholders has resolved in advance to make such repayment, and

(b) the nominal value of the ordinary shares concerned has been reduced with an equal amount by way of an amendment to the Articles of Association of the company.

The term “net profits” includes anticipated profits that have yet to be realized.

Notwithstanding the above, no withholding is required in the event of a repurchase of ordinary shares, if certain conditions are fulfilled.

If a Shareholder is resident or deemed to be resident in the Netherlands or, in case of an individual, has opted to be treated as if resident in Netherlands, such Shareholder is generally entitled to an exemption or a full credit for any Dutch dividend withholding tax against his Dutch (corporate) income tax liability and to a refund of any residual Dutch dividend withholding tax.

If a Shareholder is resident in a country other than the Netherlands under circumstances exemptions from, reduction in or refunds of, dividend withholding tax may be available pursuant to Dutch domestic law or treaties or regulations for the avoidance of double taxation.

According to Dutch domestic anti-dividend stripping rules, no credit against Dutch (corporate) income tax, exemption from, reduction in or refund of, Dutch dividend withholding tax will be granted if the recipient of the dividend paid by the company is not considered to be the beneficial owner (uiteindelijk gerechtigde) of such dividends as meant in these rules.

This section does not purport to describe the possible Dutch tax considerations or consequences that may be relevant to a Shareholder:

The description of certain Dutch tax consequences in this paragraph is only intended for the following Shareholders:

(a) individuals who are resident or deemed to be resident in the Netherlands for Dutch income tax purposes

(b) individuals who opt to be treated as if resident in the Netherlands for Dutch income tax purposes ((a) and (b) jointly “Dutch Individuals”); and

(c) entities that are subject to the CITA and are resident or deemed to be resident in the Netherlands for corporate income tax purposes “Dutch Corporate Entities”).

Dutch Individuals engaged or deemed to be engaged in an enterprise or in miscellaneous activities

Dutch Individuals are generally subject to income tax at statutory progressive rates with a maximum of 52% with respect to any benefits derived or deemed to be derived from Dutch Enterprise Shares (as defined below), including any capital gains realized on the disposal thereof.

“Dutch Enterprise Shares” are shares or any right to derive benefits from shares:

Dutch Individuals are generally subject to income tax at statutory rate of 25% with respect to any benefits derived or deemed to be derived from shares, excluding Dutch Enterprise Shares, (including any capital gains realized on the disposal thereof) that are attributable to a (fictitious) substantial interest (such shares being “Substantial Interest Shares”).

Generally, a Shareholder has a substantial interest (aanmerkelijk belang) in the company if such Shareholder, alone or together with his partner, directly or indirectly:

A Shareholder will also have a substantial interest if his partner or one of certain relatives of the Shareholder or of his partner has a substantial interest.

Generally, a Shareholder has a fictitious substantial interest (fictief aanmerkelijk belang) in the company if, without having an actual substantial interest in the company:

Dutch Individuals not engaged or deemed to be engaged in an enterprise or in miscellaneous activities or having a (fictitious) substantial interest

Generally, a Dutch Individual who owns shares, excluding Dutch Enterprise Shares and Substantial Interest Shares, will be subject annually to an income tax imposed on a fictitious yield on such shares under the regime for savings and investments (inkomen uit sparen en beleggen). Irrespective of the actual income or capital gains realized, the annual taxable benefit of all the assets and liabilities of a Dutch Individual that are taxed under this regime, including the shares, is set at a fixed amount. The fixed amount equals 4% of the fair market value of the assets reduced by the liabilities and measured, in general, exclusively at the beginning of every calendar year. The tax rate under the regime for savings and investments is a flat rate of 30%.

Dutch Corporate Entities are generally subject to corporate income tax at statutory rates up to 25% with respect to any benefits derived or deemed to be derived (including any capital gains realized on the disposal) of shares.

A Shareholder other than a Dutch Individual or Dutch Corporate Entity, will not be subject to any Dutch Taxes on income or capital gains with respect to the ownership and disposal of the shares, other than dividend withholding tax as described above, except if:

No Dutch gift or inheritance tax is due in respect of any gift of the shares by, or inheritance of the shares on the death of, a Shareholder, except if:

For purposes of Dutch gift or inheritance tax, an individual who is of Dutch nationality will be deemed to be resident in the Netherlands if he has been resident in the Netherlands at any time during the ten years preceding the date of the gift or his death. For purposes of Dutch gift tax, any individual, irrespective of his nationality, will be deemed to be resident in the Netherlands if he has been resident in the Netherlands at any time during the 12 months preceding the date of the gift.

No other Dutch Taxes, including turnover tax and taxes of a documentary nature, such as capital tax, stamp or registration tax or duty, are payable by or on behalf of a Shareholder by reason only of the purchase, ownership and disposal of the ordinary shares.

A Shareholder will not become resident, or deemed resident in the Netherlands for tax purposes by reason only of holding the ordinary shares.

In the opinion of Davis Polk & Wardwell LLP, the following is a description of the material U.S. federal income tax consequences to the U.S. Holders described below of owning and disposing of ordinary shares. It is not a comprehensive description of all tax considerations that may be relevant to a particular person’s decision to acquire securities. This discussion applies only to a U.S. Holder that holds ordinary shares as capital assets for tax purposes. In addition, it does not describe all of the tax consequences that may be relevant in light of a U.S. Holder’s particular circumstances, including alternative minimum tax consequences, the potential application of the provisions of the Code known as the Medicare contribution tax, and tax consequences applicable to U.S. Holders subject to special rules, such as:

If an entity that is classified as a partnership for U.S. federal income tax purposes holds ordinary shares, the U.S. federal income tax treatment of a partner will generally depend on the status of the partner and the activities of the partnership. Partnerships holding ordinary shares and partners in such partnerships are encouraged to consult their own tax advisers as to the particular U.S. federal income tax consequences of holding and disposing of ordinary shares.

The discussion is based on the Code, administrative pronouncements, judicial decisions, final, temporary and proposed Treasury Regulations, and the income tax treaty between the Netherlands and the United States (the “Treaty”) all as of the date hereof, changes to any of which may affect the tax consequences described herein—possibly with retroactive effect.

A “U.S. Holder” is a holder who, for U.S. federal income tax purposes, is a beneficial owner of ordinary shares who is eligible for the benefits of the Treaty and is:

(2) a corporation, or other entity taxable as a corporation, created or organized in or under the laws of the United States, any state therein or the District of Columbia; or

(3) an estate or trust the income of which is subject to U.S. federal income taxation regardless of its source.

U.S. Holders are encouraged to consult their own tax advisers concerning the U.S. federal, state, local and foreign tax consequences of owning and disposing of ordinary shares in their particular circumstances.

Subject to the passive foreign investment company rules described below, distributions paid on ordinary shares, other than certain pro rata distributions of ordinary shares, will generally be treated as dividends to the extent paid out of our current or accumulated earnings and profits (as determined under U.S. federal income tax principles). Because we do not maintain calculations of our earnings and profits under U.S. federal income tax principles, we expect that distributions generally will be reported to U.S. Holders as dividends. Subject to applicable limitations, dividends paid to certain non-corporate U.S. Holders may be taxable at preferential rates applicable to long-term capital gain. The amount of a dividend will include any amounts withheld by us in respect of Dutch income taxes. The amount of the dividend will be treated as foreign-source dividend income to U.S. Holders and will not be eligible for the dividends-received deduction generally available to U.S. corporations under the Code. Dividends will be included in a U.S. Holder’s income on the date of the U.S. Holder’s receipt of the dividend. The amount of any dividend income paid in euros will be the U.S. dollar amount calculated by reference to the exchange rate in effect on the date of actual or constructive receipt, regardless of whether the payment is in fact converted into U.S. dollars. If the dividend is converted into U.S. dollars on the date of receipt, a U.S. Holder should not be required to recognize foreign currency gain or loss in respect of the dividend income. A U.S. Holder may have foreign currency gain or loss if the dividend is converted into U.S. dollars after the date of receipt.

Subject to applicable limitations, some of which vary depending upon the U.S. Holder’s particular circumstances, Dutch income taxes withheld from dividends on ordinary shares at a rate not exceeding the rate provided by the Treaty will be creditable against the U.S. Holder’s U.S. federal income tax liability. The rules governing foreign tax credits are complex and U.S. Holders should consult their tax advisers regarding the creditability of foreign taxes in their particular circumstances. In lieu of claiming a foreign tax credit, U.S. Holders may, at their election, deduct foreign taxes, including any Dutch income tax, in computing their taxable income, subject to generally applicable limitations under U.S. law. An election to deduct foreign taxes instead of claiming foreign tax credits applies to all foreign taxes paid or accrued in the taxable year.

Subject to the passive foreign investment company rules described below, gain or loss realized on the sale or other taxable disposition of ordinary shares will be capital gain or loss, and will be long-term capital gain or loss if the U.S. Holder held the ordinary shares for more than one year. The amount of the gain or loss will equal the difference between the U.S. Holder’s tax basis in the ordinary shares disposed of and the amount realized on the disposition, in each case as determined in U.S. dollars. This gain or loss will generally be U.S.-source gain or loss for foreign tax credit purposes. The deductibility of capital losses is subject to limitations.

Under the Code, we will be a PFIC for any taxable year in which, after the application of certain “look-through” rules with respect to subsidiaries, either (i) 75% or more of our gross income

consists of “passive income,” or (ii) 50% or more of the average quarterly value of our assets consist of assets that produce, or are held for the production of, “passive income.” Passive income generally includes interest, dividends, rents, certain non-active royalties and capital gains. Whether we will be a PFIC in any year depends on the composition of our income and assets, and the relative fair market value of our assets from time to time, which we expect may vary substantially over time. Because (i) we currently own, and will own after the completion of this offering, a substantial amount of passive assets, including cash, and (ii) the values of our assets, including our intangible assets, that generate non-passive income for PFIC purposes, is uncertain and may vary substantially over time, it is uncertain whether we will be, and there can be no assurance that we will not be a PFIC in 2013 or any future years. If we are a PFIC for any year during which a U.S. Holder holds ordinary shares, we generally would continue to be treated as a PFIC with respect to that U.S. Holder for all succeeding years during which the U.S. Holder holds ordinary shares, even if we ceased to meet the threshold requirements for PFIC status.

If we are a PFIC for any taxable year during which a U.S. Holder holds ordinary shares, the U.S. Holder may be subject to adverse tax consequences. Generally, gain recognized upon a disposition (including, under certain circumstances, a pledge) of ordinary shares by the U.S. Holder would be allocated ratably over the U.S. Holder’s holding period for such shares. The amounts allocated to the taxable year of disposition and to years before we became a PFIC would be taxed as ordinary income. The amount allocated to each other taxable year would be subject to tax at the highest rate in effect for that taxable year for individuals or corporations, as appropriate, and would be increased by an additional tax equal to interest on the resulting tax deemed deferred with respect to each such other taxable year. Further, to the extent that any distribution received by a U.S. Holder on its ordinary shares exceeds 125% of the average of the annual distributions on such ordinary shares received during the preceding three years or the U.S. Holder’s holding period, whichever is shorter, that distribution would be subject to taxation in the same manner described immediately above with respect to gain on disposition

Alternatively, if we are a PFIC and if our ordinary shares are “regularly traded” on a “qualified exchange,” a U.S. Holder could make a mark-to-market election that would result in tax treatment different from the general tax treatment described in the preceding paragraph. Our ordinary shares would be treated as “regularly traded” in any calendar year in which more than a de minimis quantity of the ordinary shares, are traded on a qualified exchange on at least 15 days during each calendar quarter. The Nasdaq Global Market is a qualified exchange for this purpose. If a U.S. Holder makes the mark-to-market election, the U.S. Holder generally will recognize as ordinary income any excess of the fair market value of the ordinary shares at the end of each taxable year over their adjusted tax basis, and will recognize an ordinary loss in respect of any excess of the adjusted tax basis of the ordinary shares over their fair market value at the end of the taxable year (but only to the extent of the net amount of income previously included as a result of the mark-to-market election). If a U.S. Holder makes the election, the U.S. Holder’s tax basis in the ordinary shares will be adjusted to reflect these income or loss amounts. Any gain recognized on the sale or other disposition of ordinary shares in a year when we are a PFIC will be treated as ordinary income and any loss will be treated as an ordinary loss (but only to the extent of the net amount of income previously included as a result of the mark-to-market election).

A timely election to treat a PFIC as a qualified electing fund under Section 1295 of the Code would result in alternative treatment. U.S. Holders should be aware, however, that we do not intend to satisfy the record-keeping and other requirements that would permit U.S. Holders to make qualified electing fund elections if we were a PFIC.

In addition, if we are a PFIC or, with respect to particular U.S. Holders, are treated as a PFIC for the taxable year in which we paid a dividend or for the prior taxable year, the preferential rates discussed above with respect to dividends paid to certain non-corporate U.S. Holders would not apply.

If a U.S. Holder owns ordinary shares during any year in which we are a PFIC, the holder generally must file an IRS Form 8621, generally with the holder’s federal income tax return for that year.

U.S. Holders should consult their tax advisers regarding whether we are or or may become a PFIC and the potential application of the PFIC rules.

Payments of dividends and sales proceeds that are made within the United States or through certain U.S.-related financial intermediaries generally are subject to information reporting, and may be subject to backup withholding, unless (i) the U.S. Holder is a corporation or other exempt recipient or (ii) in the case of backup withholding, the U.S. Holder provides a correct taxpayer identification number and certifies that it is not subject to backup withholding.

The amount of any backup withholding from a payment to a U.S. Holder will be allowed as a credit against the holder’s U.S. federal income tax liability and may entitle it to a refund, provided that the required information is timely furnished to the IRS.

Certain U.S. Holders who are individuals may be required to report information relating to their ownership of an interest in certain foreign financial assets, including stock of a non-U.S. person, generally on Form 8938, subject to exceptions (including an exception for stock held through a U.S. financial institution). U.S. Holders should consult their tax advisers regarding their reporting obligations with respect to ordinary shares.

We are offering the ordinary shares described in this prospectus through a number of underwriters. J.P. Morgan Securities LLC is acting as book running manager of the offering and as representative of the underwriters. We have entered into an underwriting agreement with the underwriters. Subject to the terms and conditions of the underwriting agreement, we have agreed to sell to the underwriters, and each underwriter has severally agreed to purchase, at the public offering price less the underwriting discounts and commissions set forth on the cover page of this prospectus, the number of ordinary shares listed next to its name in the following table:

The underwriters are committed to purchase all the ordinary shares offered by us if they purchase any shares. The underwriting agreement also provides that if an underwriter defaults, the purchase commitments of non-defaulting underwriters may also be increased or the offering may be terminated.

The underwriters propose to offer the ordinary shares directly to the public at the initial public offering price set forth on the cover page of this prospectus and to certain dealers at that price less a concession not in excess of $ per share. Any such dealers may resell shares to certain other brokers or dealers at a discount of up to $ per share from the initial public offering price. After the initial public offering of the shares, the offering price and other selling terms may be changed by the underwriters. Sales of shares made outside of the United States may be made by affiliates of the underwriters.

The underwriters have an option to buy up to additional ordinary shares from us to cover sales of shares by the underwriters which exceed the number of shares specified in the table above. The underwriters have 30 days from the date of this prospectus to exercise this over-allotment option. If any shares are purchased with this over-allotment option, the underwriters will purchase shares in approximately the same proportion as shown in the table above. If any additional ordinary shares are purchased, the underwriters will offer the additional shares on the same terms as those on which the shares are being offered.

The underwriting fee is equal to the public offering price per ordinary share less the amount paid by the underwriters to us per ordinary share. The underwriting fee is $ per share. The following table shows the per share and total underwriting discounts and commissions to be paid to the underwriters assuming both no exercise and full exercise of the underwriters’ option to purchase additional shares.

We estimate that the total expenses of this offering, including registration, filing and listing fees, printing fees and legal and accounting expenses, but excluding the underwriting discounts and commissions, will be approximately $ .

A prospectus in electronic format may be made available on the web sites maintained by one or more underwriters, or selling group members, if any, participating in the offering. The underwriters may agree to allocate a number of shares to underwriters and selling group members for sale to their online brokerage account holders. Internet distributions will be allocated by the representatives to underwriters and selling group members that may make Internet distributions on the same basis as other allocations.

We have agreed that we will not (i) offer, pledge, announce the intention to sell, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase or otherwise dispose of, directly or indirectly, or file with the Securities and Exchange Commission a registration statement under the Securities Act relating to, any of our ordinary shares or securities convertible into or exchangeable or exercisable for any of our ordinary shares, or publicly disclose the intention to make any offer, sale, pledge, disposition or filing, or (ii) enter into any swap or other arrangement that transfers all or a portion of the economic consequences associated with the ownership of any ordinary shares or any such other securities (regardless of whether any of these transactions are to be settled by the delivery of ordinary shares or such other securities, in cash or otherwise), in each case without the prior written consent of J.P. Morgan Securities LLC for a period of 180 days after the date of this prospectus, other than the ordinary shares to be sold hereunder.

Our directors and executive officers, and certain of our significant shareholders have entered into lock up agreements with the underwriters prior to the commencement of this offering pursuant to which each of these persons or entities, with limited exceptions, for a period of 180 days after the date of this prospectus, may not, without the prior written consent of J.P. Morgan Securities LLC, (1) offer, pledge, announce the intention to sell, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, or otherwise transfer or dispose of, directly or indirectly, any of our ordinary shares or any securities convertible into or exercisable or exchangeable for our ordinary shares (including, without limitation, ordinary shares or such other securities which may be deemed to be beneficially owned by such directors, executive officers, managers and members in accordance with the rules and regulations of the SEC and securities which may be issued upon exercise of a stock option or warrant) or (2) enter into any swap or other agreement that transfers, in whole or in part, any of the economic consequences of ownership of the ordinary shares or such other securities, whether any such transaction described in clause (1) or (2) above is to be settled by

delivery of ordinary shares or such other securities, in cash or otherwise, or (3) make any demand for or exercise any right with respect to the registration of any of our ordinary shares or any security convertible into or exercisable or exchangeable for our ordinary shares.

We have agreed to indemnify the underwriters against certain liabilities, including liabilities under the Securities Act.

We intend to apply to have our ordinary shares approved for listing on Nasdaq under the symbol “RNA.”

In connection with this offering, the underwriters may engage in stabilizing transactions, which involves making bids for, purchasing and selling ordinary shares in the open market for the purpose of preventing or retarding a decline in the market price of the ordinary shares while this offering is in progress. These stabilizing transactions may include making short sales of the ordinary shares, which involves the sale by the underwriters of a greater number of ordinary shares than they are required to purchase in this offering, and purchasing ordinary shares on the open market to cover positions created by short sales. Short sales may be “covered” shorts, which are short positions in an amount not greater than the underwriters’ over-allotment option referred to above, or may be “naked” shorts, which are short positions in excess of that amount. The underwriters may close out any covered short position either by exercising their over-allotment option, in whole or in part, or by purchasing shares in the open market. In making this determination, the underwriters will consider, among other things, the price of shares available for purchase in the open market compared to the price at which the underwriters may purchase shares through the over-allotment option. A naked short position is more likely to be created if the underwriters are concerned that there may be downward pressure on the price of the ordinary shares in the open market that could adversely affect investors who purchase in this offering. To the extent that the underwriters create a naked short position, they will purchase shares in the open market to cover the position.

The underwriters have advised us that, pursuant to Regulation M of the Securities Act, they may also engage in other activities that stabilize, maintain or otherwise affect the price of the ordinary shares, including the imposition of penalty bids. This means that if the representatives of the underwriters purchase ordinary shares in the open market in stabilizing transactions or to cover short sales, the representatives can require the underwriters that sold those shares as part of this offering to repay the underwriting discount received by them.

These activities may have the effect of raising or maintaining the market price of the ordinary shares or preventing or retarding a decline in the market price of the ordinary shares, and, as a result, the price of the ordinary shares may be higher than the price that otherwise might exist in the open market. If the underwriters commence these activities, they may discontinue them at any time. The underwriters may carry out these transactions on Nasdaq, in the over the counter market or otherwise.

Prior to this offering, there has been no public market for our ordinary shares. The initial public offering price will be determined by negotiations between us and the representatives of the underwriters. In determining the initial public offering price, we and the representatives of the underwriters expect to consider a number of factors including:

Neither we nor the underwriters can assure investors that an active trading market will develop for our ordinary shares, or that the shares will trade in the public market at or above the initial public offering price.

Other than in the United States, no action has been taken by us or the underwriters that would permit a public offering of the securities offered by this prospectus in any jurisdiction where action for that purpose is required. The securities offered by this prospectus may not be offered or sold, directly or indirectly, nor may this prospectus or any other offering material or advertisements in connection with the offer and sale of any such securities be distributed or published in any jurisdiction, except under circumstances that will result in compliance with the applicable rules and regulations of that jurisdiction. Persons into whose possession this prospectus comes are advised to inform themselves about and to observe any restrictions relating to the offering and the distribution of this prospectus. This prospectus does not constitute an offer to sell or a solicitation of an offer to buy any securities offered by this prospectus in any jurisdiction in which such an offer or a solicitation is unlawful.

This document is only being distributed to and is only directed at (i) persons who are outside the United Kingdom or (ii) to investment professionals falling within Article 19(5) of the Financial Services and Markets Act 2000 (Financial Promotion) Order 2005 (the “Order”) or (iii) high net worth entities, and other persons to whom it may lawfully be communicated, falling with Article 49(2)(a) to (d) of the Order (all such persons together being referred to as “relevant persons”). The securities are only available to, and any invitation, offer or agreement to subscribe, purchase or otherwise acquire such securities will be engaged in only with, relevant persons. Any person who is not a relevant person should not act or rely on this document or any of its contents.

In relation to each Member State of the European Economic Area which has implemented the Prospectus Directive (each, a “Relevant Member State”), from and including the date on which the European Union Prospectus Directive (the “EU Prospectus Directive”) was implemented in that Relevant Member State (the “Relevant Implementation Date”) an offer of securities described in this prospectus may not be made to the public in that Relevant Member State prior to the publication of a prospectus in relation to the shares which has been approved by the competent authority in that Relevant Member State or, where appropriate, approved in another Relevant Member State and notified to the competent authority in that Relevant Member State, all in accordance with the EU Prospectus Directive, except that, with effect from and including the Relevant Implementation Date, an offer of securities described in this prospectus may be made to the public in that Relevant Member State at any time:

For the purposes of this provision, the expression an “offer of securities to the public” in relation to any securities in any Relevant Member State means the communication in any form and by any means of sufficient information on the terms of the offer and the securities to be offered so as to enable an investor to decide to purchase or subscribe for the securities, as the same may be varied in that Member State by any measure implementing the EU Prospectus Directive in that Member State. The expression “EU Prospectus Directive” means Directive 2003/71/EC (and any amendments thereto, including the 2010 PD Amending Directive, to the extent implemented in the Relevant Member State) and includes any relevant implementing measure in each Relevant Member State, and the expression “2010 PD Amending Directive” means Directive 2010/73/EU.

Certain of the underwriters and their affiliates have provided in the past to us and our affiliates and may provide from time to time in the future certain commercial banking, financial advisory, investment banking and other services for us and such affiliates in the ordinary course of their business, for which they have received and may continue to receive customary fees and commissions. In addition, from time to time, certain of the underwriters and their affiliates may effect transactions for their own account or the account of customers, and hold on behalf of themselves or their customers, long or short positions in our debt or equity securities or loans, and may do so in the future.

We estimate that our expenses in connection with this offering, other than underwriting discounts and commissions, will be as follows:

All amounts in the table are estimates except the U.S. Securities and Exchange Commission registration fee, the Nasdaq listing fee and the FINRA filing fee. We will pay all of the expenses of this offering.

The validity of our ordinary shares and certain other matters of Dutch law will be passed upon for us by De Brauw Blackstone Westbroek N.V. Certain matters of U.S. federal and New York State law will be passed upon for us by Davis Polk & Wardwell LLP, New York, New York. The underwriters have been represented in connection with this offering by Skadden, Arps, Slate, Meagher & Flom LLP, New York, New York.

The financial statements as of December 31, 2012 and 2011 and for each of the two years in the period ended December 31, 2012 included in this Prospectus and Registration Statement have been so included in reliance on the report of PricewaterhouseCoopers Accountants N.V., an independent registered public accounting firm, given on the authority of said firm as experts in auditing and accounting.

The current address of PricewaterhouseCoopers Accountants N.V. is Thomas R. Malthusstraat 5, 1066 JR Amsterdam, the Netherlands.

The United States and the Netherlands currently do not have a treaty providing for the reciprocal recognition and enforcement of judgments, other than arbitration awards, in civil and commercial matters. Consequently, a final judgment for payment given by a court in the United States, whether or not predicated solely upon U.S. securities laws, would not automatically be recognized or enforceable in the Netherlands. In order to obtain a judgment which is enforceable in the Netherlands, the party in whose favor a final and conclusive judgment of the U.S. court has been rendered will be required to file its claim with a court of competent jurisdiction in the Netherlands. Such party may submit to the Dutch court the final judgment rendered by the U.S. court. If and to the extent that the Dutch court finds that the jurisdiction of the U.S. court has been based on grounds which are internationally acceptable and that proper legal procedures have been observed, the court of the Netherlands will, in principle, give binding effect to the judgment of the U.S. court, unless such judgment contravenes principles of public policy of the Netherlands. Dutch courts may deny the recognition and enforcement of punitive damages or other awards. Moreover, a Dutch court may reduce the amount of damages granted by a U.S. court and recognize damages only to the extent that they are necessary to compensate actual losses or damages. Enforcement and recognition of judgments of U.S. courts in the Netherlands are solely governed by the provisions of the Dutch Civil Procedure Code.

Dutch civil procedure differs substantially from U.S. civil procedure in a number of respects. Insofar as the production of evidence is concerned, U.S. law and the laws of several other jurisdictions based on common law provide for pre-trial discovery, a process by which parties to the proceedings may prior to trial compel the production of documents by adverse or third parties and the deposition of witnesses. Evidence obtained in this manner may be decisive in the outcome of any proceeding. No such pre-trial discovery process exists under Dutch law.

We have filed with the U.S. Securities and Exchange Commission a registration statement (including amendments and exhibits to the registration statement) on Form F-1 under the Securities Act. This prospectus, which is part of the registration statement, does not contain all of the information set forth in the registration statement and the exhibits and schedules to the registration statement. For further information, we refer you to the registration statement and the exhibits and schedules filed as part of the registration statement. If a document has been filed as an exhibit to the registration statement, we refer you to the copy of the document that has been filed. Each statement in this prospectus relating to a document filed as an exhibit is qualified in all respects by the filed exhibit.

Upon completion of this offering, we will become subject to the informational requirements of the Exchange Act. Accordingly, we will be required to file reports and other information with the SEC, including annual reports on Form 20-F and reports on Form 6-K. You may inspect and copy reports and other information filed with the SEC at the Public Reference Room at 100 F Street, N.E., Washington, D.C. 20549. Information on the operation of the Public Reference Room may be obtained by calling the SEC at 1-800-SEC-0330. In addition, the SEC maintains an Internet website that contains reports and other information about issuers, like us, that file electronically with the SEC. The address of that website is www.sec.gov.

As a foreign private issuer, we are exempt under the Exchange Act from, among other things, the rules prescribing the furnishing and content of proxy statements, and our executive officers, directors and principal shareholders are exempt from the reporting and short-swing profit recovery provisions contained in Section 16 of the Exchange Act. In addition, we will not be required under the Exchange Act to file periodic reports and financial statements with the SEC as frequently or as promptly as U.S. companies whose securities are registered under the Exchange Act.

We will send the transfer agent a copy of all notices of shareholders’ meetings and other reports, communications and information that are made generally available to shareholders. The transfer agent has agreed to mail to all shareholders a notice containing the information (or a summary of the information) contained in any notice of a meeting of our shareholders received by the transfer agent and will make available to all shareholders such notices and all such other reports and communications received by the transfer agent.

The notes are an integral part of these condensed consolidated financial statements.

The activities of Prosensa Holding B.V. and its subsidiaries (together the company) primarily consist of developing innovative, RNA based therapeutics to fill unmet medical needs for patients with genetic diseases.

The company is a B.V. and is incorporated and domiciled in the Netherlands. The address of its registered office is J.H. Oortweg 21, Leiden. Prosensa Holding B.V. is the ultimate parent of the following group of entities:

The shares of Prosensa Holding B.V. are held by multiple shareholders, none of them having a share in the company in excess of 25%.

The condensed consolidated financial statements of Prosensa have been prepared in accordance with International Financial Reporting Standards (IFRS) as issued by the International Accounting Standards Board (IASB). There are no material differences between IFRS as adopted by the European Union and IFRS as adopted by the IASB.

The condensed consolidated financial statements of the company were prepared in accordance with IFRS for interim financial information (IAS 34). Certain information and disclosures normally included in consolidated financial statements prepared in accordance with IFRS have been condensed or omitted. Accordingly, these condensed consolidated financial statements should be read in conjunction with the company’s annual consolidated financial statements for the year ended December 31, 2012 and accompanying notes.

The preparation of financial statements in conformity with IFRS requires the use of certain critical accounting estimates. It also requires management to exercise its judgment in the process of applying the company’s accounting policies. The areas involving a higher degree of judgment or complexity, or areas where assumptions and estimates are significant to the condensed consolidated financial statements are disclosed in note 4.

The following standards and amendments to standards became effective for annual periods on January 1, 2013 and have been adopted by the company in the preparation of the condensed consolidated financial statements:

The adoption of these new standards and amendments to standards did not impact the company’s financial position or results of operations. The adoption of IFRS 13, “Fair value measurement”, resulted in revised disclosure of the company’s fair value measurements. Refer to note 3.2 of these condensed consolidated financial statements for further information.

The only standard which could have a significant effect on the condensed consolidated financial statements of the company is IFRS 9 “Financial Instruments”. IFRS 9 is the first step in the process of replacing IAS 39 “Financial Instruments: Recognition and Measurement”. The standard is not applicable until January 1, 2015, but is available for early adoption. The company has yet to assess IFRS 9’s full impact and intends to adopt IFRS 9 no later than January 1, 2015. None of the other standards (e.g. amendments to IFRS 10, 12 or IAS 27) are expected to have a significant effect on the condensed consolidated financial statements of the company.

Subsidiaries are all entities over which the company has the power to govern the financial and operating policies generally accompanying a shareholding of more than 50% of the voting rights. The existence and effect of potential voting rights that are currently exercisable or convertible are considered when assessing whether the company controls another entity. Subsidiaries are fully consolidated from the date on which control is transferred to the company. They are de-consolidated from the date that control ceases.

Inter-company transactions, balances, income and expenses on transactions between group companies are eliminated. Profits and losses resulting from inter-company transactions that are recognized in assets are also eliminated. Accounting policies of subsidiaries have been changed where necessary to ensure consistency with the policies adopted by the company.

The condensed consolidated financial statements do not include all financial risk management information and disclosures required in the annual consolidated financial statements, and should be read in conjunction with the company’s annual consolidated financial statements for the period ended December 31, 2012.

There have been no changes in the financial management team that is responsible for financial risk management or in the financial risk management policies since December 31, 2012.

The company has entered into a floating-to-fixed interest rate swap to reduce the impact of volatility in changes to interest rates. The determined fair value of the interest rate swap is the impact between a fixed interest rate of 4.15% and the estimated interest rate at measurement date for the remaining period of the instrument discounted over time. The estimated interest rate and discount rates are level two fair value hierarchy inputs. As of March 31, 2013 and 2012 the change in fair value of the interest rate swap which was recorded through the profit and loss statement amounted to a 3 thousand gain and a nil thousand loss, respectively. The interest rate swap is recorded as both a non-current and current liability in the consolidated balance sheet.

The class A and class B equity shares as issued by the company contain an embedded derivative. This derivative is meant to protect the holders of class A and B equity shares against potential dilution of their equity. The embedded derivative is not recorded in the consolidated balance sheet as its value was determined to be insignificant because the anti-dilution option only applies when the class A and B equity shares decreases over time which is currently not the estimate.

An independent valuation firm performed a valuation as of September 30, 2012 and December 5, 2012 on the enterprise value which was allocated to the preferred shares and ordinary shares using the current value method (CVM) and option pricing method (OPM). In determining the aggregate enterprise value three generally accepted approaches were considered: income approach, market approach and cost approach. Based on the stage of development and information available, the company has determined that the income approach is the most appropriate method, and when applicable, the company has also employed the prior sale of company stock method to estimate the aggregate enterprise value.

The preparation of financial statements in conformity with IFRS requires the company to make estimates and assumptions that affect the reported amounts and classifications of assets and liabilities, revenues and expenses in the condensed consolidated financial statements. The estimates that have a significant risk of causing a material adjustment to the financial statements are utilized for share-based compensation, income taxes, research and development expenditures and borrowings. Actual results could differ materially from those estimates and assumptions.

The preparation of financial statements in conformity with IFRS also requires the company to exercise judgment in applying the accounting policies. Critical judgments in the application of the company’s accounting policies relate to income taxes, research and development expenditures and revenue and the cost of license revenue.

In the first quarter of 2013 the company engaged professional advisors to explore a capital markets transaction. Advisors invoiced the company for a total of €572,000 for services performed

until March 31, 2013. These expenses were recorded in G & A expense, because a capital markets transaction is deemed not probable as of March 31, 2013.

The condensed consolidated financial statements do not include all disclosures for critical accounting estimates and judgments that are required in the annual consolidated financial statements, and should be read in conjunction with the company’s annual consolidated financial statements for the period ended December 31, 2012.

The company‘s financial results have varied substantially, and are expected to continue to vary, from quarter to quarter. The company therefore believes that period to period comparisons should not be relied upon as indicative of future financial results.

The company operates in one reportable segment, which comprises the discovery and development of innovative, RNA based therapeutics. The Management Board is identified as the chief operating decision maker. The Management Board reviews the consolidated operating results regularly to make decisions about the resources and to assess overall performance.

The company derives its revenues currently from a single party, GSK (based in the United Kingdom). The company and GSK have entered into an exclusive worldwide collaboration for the development and commercialization of RNA based therapeutics for DMD. In October 2009 the company signed a Research & Development and Collaboration & License agreement with GSK to which the 2013 and 2012 net revenues both relate.

The amounts provided to the Management Board with respect to total assets and liabilities are measured in a manner consistent with that of the financial statements.

Depreciation expense of €199 thousand for the three months ended March 31, 2013 (three months ended March 31, 2012: €189 thousand) has been charged in research and development costs. Depreciation expense of €48 thousand for the three months ended March 31, 2013 (three months ended March 31, 2012: €46 thousand) has been charged in general and administrative costs.

The company made commitments to purchase laboratory and office equipment which had not been received as of March 31, 2013 in the amount of €21 thousand.

Amortization expense of €40 thousand for the three months ended March 31, 2013 (three months ended March 31, 2012: €32 thousand) has been charged in research and development costs. Amortization expense of €18 thousand for the three months ended March 31, 2013 (three months ended March 31, 2012: €24 thousand) has been charged in general and administrative costs.

The restricted cash balance secures a bank loan. Refer to note 12 of these condensed consolidated financial statements for further detail.

The fair value of trade and other receivables approximates their carrying value. As of March 31, 2013, no trade receivables and other receivables were impaired or not performing. The carrying amount of the company’s trade receivables is mostly denominated in British Pounds, while other receivables are denominated in Euros.

The other classes within trade and other receivables do not contain impaired assets. The maximum exposure to credit risk at the reporting date is the carrying value of each class of receivable mentioned above. The group does not hold any collateral as security.

Prepayments mainly relate to prepaid rent and insurance as of March 31, 2013 and 2012.

In 2006 the company received a bank loan of €900 thousand from ABN Amro N.V. An amount of €500 thousand secures the bank loan and is therefore considered restricted cash and recorded as a component of other financial assets. The remaining balance is at the free disposal of the company.

The total authorized number of common shares as of March 31, 2013 is 21 million shares (as of December 31, 2012: 21 million shares). The par value as of March 31, 2013 is €0.01 per share (as of December 31, 2012: €0.01 per share). All issued shares are fully paid.

Besides the minimum amount of share capital to be held under Dutch law, there are no distribution restrictions applicable to equity of the company.

On January 16, 2012, the company concluded an agreement for new equity financing led by a new investor, New Enterprise Associates, and supported by existing Prosensa investors: Abingworth, Life Sciences Partners, Gimv, Idinvest Partners and Medsciences Capital. As a result of this agreement, the company issued 9,107,144 class B shares with total net proceeds of €22.7 million, of which €11.4 million was received in the three months ended March 31, 2012.

As of March 31, 2013 and December 31, 2012 other liabilities mainly consist of accruals for services provided by vendors but not yet billed, reimbursements received from research and development partners for expenses which have yet to be incurred and miscellaneous liabilities.

The condensed consolidated financial statements do not include all disclosures for borrowings that are required in the annual consolidated financial statements, and should be read in conjunction with the company’s annual consolidated financial statements for the period ended December 31, 2012.

In the three months ended March 31, 2013 an amount of €859 thousand (three months ended March 31, 2012: €859 thousand) of the initial upfront payment was recognized as license revenue in the consolidated condensed income statement.

In the three months ended March 31, 2013, the group recognized revenue of €548 thousand (three months ended March 31, 2012: €526 thousand) related to other upfront payments.

The condensed consolidated financial statements do not include all disclosures for revenue and deferred revenue that are required in the annual consolidated financial statements, and should be read in conjunction with the company’s annual consolidated financial statements for the period ended December 31, 2012.

The group leases laboratory and office space under non-cancellable operating lease agreements. The group moved its laboratories and offices to new premises in J.H. Oortweg 21 in Leiden on February 2, 2011. The lease term is 5 years. Furthermore the group entered into lease agreements for office furniture. The lease term is between 1 and 5 years.

The lease obligations end between April 2013 and February 2015. The lease expenditure charged to the income statement for the three months ended March 31, 2013 €172 thousand (three months ended March 31, 2012: €187 thousand).

The future aggregate minimum lease payments under non-cancellable operating leases are as follows:

On December 5, 2012 the company granted to the members of the management board 1.0 million options that vest only upon a liquidity event such as a change of control of the company or an initial public offering. The actual number of options subject to vesting will depend on the value of the Company’s shares in the change of control transaction or the share price development following an initial public offering. This market performance condition is included in the fair value of the options granted. As of March 31, 2013, the requirements subject to the vesting of these options are deemed not probable under an IPO scenario, and amounts are de minimis under a change of control scenario, and therefore no expenses have been recognized. Until the date an IPO is considered to be probable, no expense will be recognized for these grants.

The condensed consolidated financial statements do not include all disclosures for share-based payments that are required in the annual consolidated financial statements, and should be read in conjunction with the company’s annual consolidated financial statements for the period ended December 31, 2012.

Basic loss per share is calculated by dividing the loss attributable to equity holders of the company by the weighted average number of ordinary and preferred shares in issue during the year.

Diluted loss per share is calculated by adjusting the weighted average number of ordinary shares outstanding to assume conversion of all dilutive potential ordinary shares. Due to the fact that the company is loss making all potential ordinary shares had an antidilutive effect, if converted, and thus have been excluded from the computation of loss per share.

In the period ended March 31, 2012 and 2013 the Management Board was paid regular salaries and contributions to post employment schemes. Additionally, selected members of the Supervisory Board received compensation for their services in the form of cash compensation.

On December 5, 2012 the Management Board was granted 1.0 million stock options that vest based on non-market conditions. As of March 31, 2013 the requirements to vest are deemed not probable under an IPO scenario, and amounts are de minimus under a change of control scenario, and therefore no expenses were recognized in the income statement. Refer to note 18 of these condensed consolidated financial statements for additional information.

The condensed consolidated financial statements do not include all disclosures for related-party transactions that are required in the annual consolidated financial statements, and should be read in conjunction with the company’s annual consolidated financial statements for the period ended December 31, 2012.

No events occurred after the balance sheet date that would have a material impact on the result or financial position of the group.

In our opinion, the accompanying consolidated balance sheets and the related consolidated statements of comprehensive income, of changes in equity and of cash flows present fairly, in all material respects, the financial position of Prosensa Holding B.V. and its subsidiaries at December 31, 2012 and December 31, 2011, and the results of their operations and their cash flows for each of the two years in the period ended December 31, 2012 in conformity with International Financial Reporting Standards as issued by the International Accounting Standards Board. These financial statements are the responsibility of the Company’s management. Our responsibility is to express an opinion on these financial statements based on our audits. We conducted our audits of these statements in accordance with the standards of the Public Company Accounting Oversight Board (United States). Those standards require that we plan and perform the audit to obtain reasonable assurance about whether the financial statements are free of material misstatement. An audit includes examining, on a test basis, evidence supporting the amounts and disclosures in the financial statements, assessing the accounting principles used and significant estimates made by management, and evaluating the overall financial statement presentation. We believe that our audits provide a reasonable basis for our opinion.

The company is a B.V. which is incorporated and domiciled in the Netherlands. The address of its registered office is J.H. Oortweg 21, Leiden. Prosensa Holding B.V. is the ultimate parent of the following group of entities:

The shares of Prosensa Holding B.V. are held by multiple shareholders, none of them having a share in the company in excess of 25%.

The Management Board and Supervisory Board approved the consolidated financial statements for issuance on April 16, 2013.

The principal accounting policies applied in the preparation of these consolidated financial statements are set out below. These policies have been consistently applied to all the years presented, unless otherwise stated.

The consolidated financial statements of Prosensa have been prepared in accordance with International Financial Reporting Standards (IFRS) as issued by the International Accounting Standards Board (IASB). There are no material differences between IFRS as adopted by the European Union and IFRS as issued by the International Accounting Standards Board for the financial years 2012 and 2011. The consolidated financial statements have been prepared under the historical cost convention, as modified by derivative instruments at fair value through profit or loss.

The preparation of financial statements in conformity with IFRS requires the use of certain critical accounting estimates. It requires management to exercise its judgment in the process of applying the company’s accounting policies. The areas involving a higher degree of judgment or complexity, or areas where assumptions and estimates are significant to the consolidated financial statements are disclosed in note 4.

During the year ended December 31, 2012 it was established that the company’s borrowings were understated. The prior year balances, including the company’s opening equity as of January 1, 2011 have been revised to correct for this understatement, resulting in a increase in accumulated deficit of €160 thousand. The company’s basic and diluted loss per share for the years ended December 31, 2012 and 2011 were not impacted for the understatement nor were cash flows used in operations. The company has determined that this was not a material adjustment.

There are no IFRS standards or IFRIC interpretations that are effective for the first time for the financial year beginning on or after January 1, 2012 that had a material impact on the company.

A number of new standards and amendments to standards and interpretations are effective for annual periods beginning after January 1, 2012 and have not been applied in preparing these consolidated financial statements (e.g. IFRS 11 and IFRS 12). None of these are expected to have a significant effect on the consolidated financial statements of the company, except the following set out below:

Items included in the financial statements of each of the company’s entities are measured using the currency of the primary economic environment in which the entity operates (‘the functional currency’). The consolidated financial statements are presented in Euro (‘EUR’), which is the company’s functional and presentation currency.

Foreign currency transactions are translated into the functional currency using the exchange rates prevailing at the dates of the transactions or valuation where items are re-measured. Foreign exchange gains and losses resulting from the settlement of such transactions and from the translation at year-end exchange rates of monetary assets and liabilities denominated in foreign currencies are recognized in the income statement.

Foreign exchange gains and losses that relate to borrowings and cash and cash equivalents are presented in the income statement within ‘finance income or cost.’ All other foreign exchange gains and losses are presented in the income statement within ‘other gains / (losses) – net.’

The cash flow statement has been prepared using the indirect method. The cash disclosed in the cash flow statement is comprised of cash and cash equivalents. Cash comprises cash on hand and demand deposits. Cash equivalents are short-term, highly liquid investments that are readily convertible to known amounts of cash and are subject to an insignificant risk of changes in value. Cash flows denominated in foreign currencies have been translated at the average exchange rates. Exchange differences, if any, affecting cash items are shown separately in the cash flow statement. Interest paid and received, dividends received and income tax are included in the cash from operating activities.

Leasehold improvements and equipment comprise mainly leasehold improvements, laboratory equipment and other office equipment. Leasehold improvements and equipment are stated at historical cost less depreciation. Historical cost includes expenditure that is directly attributable to the acquisition of the items.

Subsequent costs are included in the asset’s carrying amount or recognized as a separate asset only when it is probable that future economic benefits associated with the item will flow to the company and the cost of the item can be measured reliably. The carrying amount of the replaced part is derecognized. All other repairs and maintenance are charged to the income statement during the financial period in which they are incurred.

Depreciation on leasehold improvements and equipment is calculated using the straight-line method to allocate their cost over their estimated useful lives, as follows:

Leasehold improvements are depreciated over the shorter of the expected lease term for the buildings the assets relate to or the estimated useful life.

Tangible fixed assets that are leased under a finance lease are depreciated over the shorter of the lease term or their estimated useful lives unless there is reasonable certainty that the company will obtain ownership at the end of the lease term, in which case the assets are depreciated over their estimated useful lives.

The assets’ residual values and useful lives are reviewed, and adjusted if appropriate, at the end of each reporting period.

An asset’s carrying amount is written down immediately to its recoverable amount if the asset’s carrying amount is greater than its estimated recoverable amount (note 2.8). The impairment is recognized through operating income and loss.

Gains and losses on disposals are determined by comparing the proceeds with the carrying amount and are recognized within other gains—net in the income statement.

Intangible assets comprise mainly acquired patents, licenses and software. Intangible assets are initially measured at acquisition cost or production cost, including any directly attributable costs of preparing the asset for its intended use. Amortization begins when an asset is available for use and amortization is calculated using the straight-line method to allocate their cost over their estimated useful lives, as follows:

Intangible assets are carried at cost less accumulated amortization and accumulated impairment losses. The useful lives of intangible assets are reviewed at each reporting date. The effect of any adjustment to useful lives is recognized prospectively as a change of accounting estimate.

Amortization of intangible assets is recognized on the relevant line of the income statement according to the purpose for which the asset is used.

Research expenses are recognized as expenses when incurred. Costs incurred on development projects are recognized as intangible assets as of the date as of which it can be established that it is probable that future economic benefits attributable to the asset will flow to the company considering its technological and commercial feasibility. This is generally the case when regulatory approval for commercialization is achieved and costs can be measured reliably. Given the current stage of the development of the company’s products, no development expenditures have yet been capitalized. Intellectual property-related costs for patents are part of the expenditure for the research and development projects. Therefore, registration costs for patents are expensed when incurred as long as the research and development project concerned does not meet the criteria for capitalization.

Assets that are subject to amortization are reviewed for impairment whenever events or changes in circumstances indicate the carrying amount may not be recoverable. An impairment loss is recognized as the amount by which the asset’s carrying amount exceeds its recoverable amount. The recoverable amount is the higher of an asset’s fair value less costs to sell and value in use. For the purpose of assessing impairment, assets are grouped at the lowest levels for which there are separately identifiable cash flows (cash-generating units). Non-financial assets that were previously impaired are reviewed for possible reversal of the impairment at each reporting date.

The company classifies its financial assets in the following categories: a) Financial assets at fair value through profit and loss, and b) Loans and receivables.

The classification depends on the purpose for which the financial assets were acquired. Management determines the classification of its financial assets at initial recognition.

Derivative instruments are categorized in this category as the company currently does not apply hedge accounting (note 2.13).

Loans and receivables are non-derivative financial assets with fixed or determinable payments that are not quoted in an active market. They are included in current assets, except for maturities greater than 12 months after the end of the reporting period. These are classified as non-current

assets. The company’s loans and receivables comprise ‘trade and other receivables’ as well as ‘financial assets non-current’ which relate to lease deposits on the balance sheet (note 2.15 and 2.19).

Regular purchases and sales of financial assets are recognized on the trade-date—the date on which the company commits to purchase or sell the asset. Financial assets carried at fair value through profit or loss are initially recognized at fair value, and transaction costs are expensed in the income statement. Financial assets at fair value through profit or loss are subsequently carried at fair value. Loans and receivables are subsequently carried at amortized cost using the effective interest method. Financial assets are derecognized when the rights to receive cash flows from the investments have expired or have been transferred and the company has transferred substantially all risks and rewards of ownership.

Gains arising from changes in the fair value of the ‘financial assets at fair value through profit or loss’ category are presented in the income statement within other gains—net in the period in which they arise.

Financial assets and liabilities are offset and the net amount reported in the balance sheet when there is a legally enforceable right to offset the recognized amounts and there is an intention to settle on a net basis, or realize the asset and settle the liability simultaneously.

The company assesses at the end of each reporting period whether there is objective evidence that a financial asset or group of financial assets is impaired. Impairment losses are incurred only if there is objective evidence of impairment as a result of one or more events that occurred after the initial recognition of the asset (a loss event) and that loss event (or events) has an impact on the estimated future cash flows of the financial asset or group of financial assets that can be reliably estimated.

The criteria the company uses to determine if there is objective evidence of an impairment loss include:

The amount of the loss is measured as the difference between the asset’s carrying amount and the present value of estimated future cash flows (excluding future credit losses that have not been incurred) discounted at the financial asset’s original effective interest rate. The carrying

amount of the asset is reduced either directly or through use of an allowance amount. The amount of the loss is recognized in the consolidated income statement.

If, in a subsequent period, the amount of the impairment loss decreases and the decrease can be related objectively to an event occurring after the impairment was recognized (such as an improvement in the debtor’s credit rating), the reversal of the previously recognized impairment loss is recognized in the consolidated income statement.

Derivatives are initially recognized at fair value on the date a derivative contract is entered into and are subsequently re-measured at their fair value. The resulting gain or loss is recognized in the consolidated income statement as the company currently does not apply hedge accounting.

Inventories are stated at the lower of cost and net realizable value. Cost is determined using the first-in, first-out (FIFO) method. The cost of finished goods and work in progress comprises manufacturing design and validation costs, raw materials, direct labor, other direct costs and related production overheads (based on normal operating capacity). It excludes borrowing costs.

Net realizable value is the estimated selling price in the ordinary course of business, less applicable variable selling expenses.

Trade receivables are amounts due from customers for license fee payments or services performed in the ordinary course of business. If collection is expected in one year or less (or in the normal operating cycle of the business if longer), they are classified as current assets. Trade receivables are recognized initially at fair value and subsequently measured at amortized cost using the effective interest method, less provision for impairment, if any.

Cash and cash equivalents include cash on hand, deposits held at call with banks and current accounts with banks. Bank overdrafts are shown within borrowings in current liabilities on the balance sheet. Cash equivalents are short-term, liquid investments with original maturities of three months or less that are readily convertible to known amounts of cash and are subject to an insignificant risk of changes in value. Cash balances which are not freely available for use are classified as restricted cash as a component of other financial assets (note 11).

The company classifies an instrument, or its component parts, on initial recognition as a financial liability or an equity instrument in accordance with the substance of the contractual arrangement and the definitions of a financial liability and an equity instrument.

An instrument is classified as a financial liability when it is either (i) a contractual obligation to deliver cash or another financial asset to another entity or to exchange financial assets or financial liabilities with another entity under conditions that are potentially unfavorable to the company; or (ii) a contract that will or may be settled in the company’s own equity instruments and is a non-derivative for which the company is or may be obliged to deliver a variable number

of the company’s own equity instruments or a derivative that will or may be settled other than by the exchange of a fixed amount of cash or another financial asset for a fixed number of the company’s own equity instruments.

An equity instrument is defined as any contract that evidences a residual interest in the assets of an entity after deducting all of its liabilities. An instrument is an equity instrument only if the issuer has an unconditional right to avoid settlement in cash or another financial asset.

Ordinary shares are classified as equity. Incremental costs directly attributable to the issue of new shares or options are shown in equity as a deduction from the proceeds, net of tax.

A financial instrument or its component parts are classified on initial recognition as a financial liability or a financial asset or an equity instrument in accordance with the substance of the contractual arrangement and the definitions of a financial liability or a financial asset and an equity instrument.

Pursuant to the Shareholders’ Agreement all of the outstanding preferred shares will convert into the ordinary shares upon the consummation of an Initial Public Offering (IPO). The conversion rate for the preferred shares is calculated by reference to the original issue price of relevant preferred shares, adjusted for any stock splits, share distributions and, in the case of holders of Class A and Class B preferred shares, certain anti-dilution protections. The company expects that the conversion rate upon the consummation of this offering will be one-to-one and therefore that all of the outstanding preferred shares will convert into an aggregate of 25,511,240 ordinary shares.

The company issued three classes of preference shares, Class A, Class B and Class O shares. The dividend preference is non-cumulative and is only applicable when the general meeting of shareholder’s decides to make a profit distribution (note 15).

Class A and Class B shares have a dividend preference over ordinary shares and Class O shares. In addition Class A and Class B shares have an anti-dilution protection that is not applicable for Class O and ordinary Shares. The preference can result in additional issuance of a variable number of shares. Class A and Class B shares therefore consist of an equity element and a liability element with respect to the anti-dilution protection. Class A and Class B shares are split into an equity portion and a liability portion at inception of the instrument. The fair value of the anti-dilution preference is determined and separately recorded as an embedded derivative. The remainder amount after deducting the value of the anti-dilution preference from the consideration received upon issuance of the Class A and Class B shares is classified as equity. The anti-dilution preference is measured at fair value through profit and loss. The remaining equity component is not remeasured.

Issuance costs of the Class A and Class B shares are assigned to the relative fair values of the embedded derivative and the equity component on initial recognition. The issuance costs with respect to the equity part is recognized directly in equity and not remeasured.

Class O shares have a dividend preference over ordinary shares. Class O shares qualify as equity.

Trade payables are obligations to pay for goods or services that have been acquired in the ordinary course of business from suppliers. Accounts payable are classified as current liabilities if payment is due within one year or less (or in the normal operating cycle of the business if longer). If not, they are presented as non-current liabilities.

Trade payables are recognized initially at fair value and subsequently measured at amortized cost using the effective interest method.

Borrowings are recognized initially at fair value, net of transaction costs incurred. Borrowings are subsequently carried at amortized cost; any difference between the proceeds (net of transaction costs) and the redemption value is recognized in the income statement over the period of the borrowings using the effective interest method.

The company has obtained loans from various governmental and non-profit groups. To encourage research and development , the company obtained certain loans that generally bear an interest rate below the market interest rate, considered by the company to be 12% over the last four years. The difference between fair value and the notional amount at inception is treated as a donation received for certain research performed by the company.

Certain loans from patient organizations have no fixed redemption schemes and repayment is due when certain pre-determined milestones are met. A change in estimate on the redemption date has an impact on the borrowing value at each subsequent balance sheet date. The borrowing value at a certain date equals the discounted value of the redemption using the effective interest rate. The impact of the change in estimate is reflected as financial expenses.

The tax expense for the period comprises current and deferred tax. Tax effects are recognized in the income statement, except to the extent that it relates to items recognized in other comprehensive income or directly in equity. In this case the tax is also recognized in other comprehensive income or directly in equity, respectively.

The current income tax charge is calculated on the basis of the tax laws enacted or substantively enacted at the balance sheet date in the countries where the company’s subsidiaries and associates operate and generate taxable income. Management periodically evaluates positions taken in tax returns with respect to situations in which applicable tax regulation is subject to interpretation. It establishes provisions where appropriate on the basis of amounts expected to be paid to the tax authorities.

Deferred income tax is recognized, using the liability method, on temporary differences arising between the tax basis of assets and liabilities and their carrying amounts in the consolidated financial statements. However, the deferred income tax is not accounted for if it arises from

initial recognition of an asset or liability in a transaction other than a business combination that at the time of the transaction affects neither accounting nor taxable profit and loss. Deferred income tax is determined using tax rates (and laws) that have been enacted or substantially enacted by the balance sheet date and are expected to apply when the related deferred income tax asset is realized or the deferred income tax liability is settled.

Deferred income tax assets are recognized only to the extent that it is probable that future taxable profit will be available against which the temporary differences can be utilized.

Deferred income tax is provided on temporary differences arising on investments in subsidiaries and associates, except where the timing of the reversal of the temporary difference is controlled by the company and it is probable that the temporary difference will not reverse in the foreseeable future.

Deferred income tax assets and liabilities are offset when there is a legally enforceable right to offset current tax assets against current tax liabilities and when the deferred income taxes assets and liabilities relate to income taxes levied by the same taxation authority on either the taxable entity or different taxable entities where there is an intention to settle the balances on a net basis.

The company operates a defined contribution pension plan for all employees funded through payments to an insurance company. The company has no legal or constructive obligations to pay further contributions if the fund does not hold sufficient assets to pay all employees the benefits relating to employee service in the current and prior periods. The contributions are recognized as employee benefit expense when they are due. Prepaid contributions are recognized as an asset to the extent that a cash refund or a reduction in the future payments is available.

Termination benefits are payable when employment is terminated by the company before the normal retirement date, or whenever an employee accepts voluntary redundancy in exchange for these benefits. The company recognizes termination benefits when it is demonstrably committed to either: terminating the employment of current employees according to a detailed formal plan without possibility of withdrawal; or providing termination benefits as a result of an offer made to encourage voluntary redundancy. Benefits falling due more than 12 months after the end of the reporting period are discounted to their present value.

The company recognizes a liability and an expense for bonus plans if contractually obliged or if there is a past practice that has created a constructive obligation.

The company operates share-based compensation plans, under which it receives services from directors and selected employees as consideration for equity instruments (options or restricted shares) of the company. The fair value of these equity instruments granted in exchange for the

employee services received is recognized as an expense against a credit in equity. The total amount to be expensed is determined by reference to the grant date fair value of the equity instruments granted:

Vesting conditions are included in assumptions about the number of equity instruments that are expected to vest. The total expense is recognized over the vesting period, which is the period over which all of the specified vesting conditions are to be satisfied. At the end of each reporting period, the company revises its estimates of the number of equity instruments that are expected to vest based on the non-market vesting conditions. It recognizes the impact of the revision to previous estimates, if any, in the income statement, with a corresponding adjustment to equity.

If the terms of an equity-settled award are modified at a minimum an expense is recognized as if the terms had not been modified. An additional expense is recognized for any modification that increases the total fair value of the share-based payment arrangement or is otherwise beneficial to the employee as measured at the date of modification.

Where the company is receiving employee services in a share-based payment transaction settled by a shareholder, it measures the services received as an equity-settled share-based payment transaction. The fair value of employee services received, measured by reference to the grant date fair value, is recognized over the vesting period with a corresponding adjustment to equity.

In 2012 the company granted equity-settled options to members of the Management Board, which may vest only upon a liquidity event such as a change of control of the company or an IPO and is subject to continued employment conditions until the date such an event occurs. The number of options that vest will depend on the value of the company’s shares in the change of control transaction or the share price development following an IPO. This market performance condition is included in the fair value of the options granted.

Until the date a liquidity event is considered to be probable, no expense will be recognized for these equity-settled awards. As from the date such an event is deemed to be probable, the fair value is recognized as an expense over the estimated vesting period, taking into account the services received during the period from the grant date.

The company’s share-based compensation plans qualify as equity-settled share-based payment transactions. When the options are exercised, the company issues new shares. The proceeds received net of any directly attributable transaction costs are credited to share capital (nominal value) and share premium when the options are exercised.

The social security contributions payable by the company in connection with the vesting of the share options or restricted shares is considered an integral part of the grant itself, and the charge will be treated as a cash-settled transaction. Normally, the maximum social security charge of an employee that receives option grants is already met and no additional social security charges are due.

Revenue comprises the fair value of the consideration received or receivable for the sale of licenses and services in the ordinary course of the company’s activities. Revenue is shown net of value-added tax, returns, rebates and discounts and after eliminating sales within the company.

The company recognizes revenue when the amount of revenue can be reliably measured, it is probable that future economic benefits will flow to the entity and when specific criteria have been met for each of the company’s activities as described below. The company bases its estimates on historical results, taking into consideration the type of customer, the type of transaction and the specifics of each arrangement.

Non-refundable upfront licensing fees and certain guaranteed, time-based payments that require continuing involvement in the form of research and development, manufacturing or other efforts by the company are recognized in the period of the expected performance.

Upon signing of the Research & Development and Collaboration & License agreement with GSK the company received € 17.2 million (£ 16.0 million) as a non-refundable upfront payment. The expected performance occurs on a straight line basis over the 5 year period. The company is obliged to provide research and development services regarding certain pre-defined programs in the agreement. Other upfront payments are recognized by reference to the stage of completion of the underlying agreement at the balance sheet date (also referred to as percentage of completion method) whenever the rendering of services under a license revenue agreement can be estimated reliably. The rendering of services can be estimated reliably when, in addition to general conditions mentioned further above, the following conditions are met:

When the above criteria are not met, revenue arising from the rendering of services is recognized only to the extent of the expenses recognized that are recoverable (cost-recovery approach). Costs under these types of arrangements are expensed as incurred and therefore the pattern of cost recognition may be different than revenue recognition.

Milestone payments are contingent upon the achievement of contractually stipulated targets. The achievement of these milestones depends largely on meeting specific requirements laid out in the collaboration agreement, so the related revenue is only recognized once substantive services have been performed in relation to the payment and contractual milestones have been fully achieved and confirmed by the counterparty (note 19).

Cost reimbursements to which the company is entitled to under certain agreements are recognized in the income statement in the same period of the recorded cost they intend to compensate. When the reimbursable costs are not yet invoiced these amounts are included as a component of trade and other receivables on the balance sheet.

Interest income is recognized using the effective interest method. When a loan and receivable is impaired, the company reduces the carrying amount to its recoverable amount, being the estimated future cash flow discounted at the original effective interest rate of the instrument, and continues unwinding the discount as interest income. Interest income on impaired loan and receivables are recognized using the original effective interest rate.

The company receives certain government grants, which support its research effort in defined projects. These grants generally provide for reimbursement of approved costs incurred as defined in the respective grants. Income in respect of grants includes contributions towards the costs of research and development. Income is recognized when costs under each grant are incurred in accordance with the terms and conditions of the grant and the collectability of the receivable is reasonably assured.

Government grants relating to costs are deferred and recognized in the income statement over the period necessary to match them with the costs they are intended to compensate. When the cash in relation to recognized government grants is not yet received the amount is included as a receivable on the balance sheet.

The company includes income from government grants under ‘Other income’ in the income statement.

Research expenditures are recognized as expenses when incurred except when certain criteria for capitalization as intangible assets are met (note 2.7). At each balance sheet date, the company estimates the level of service performed by the vendors and the associated cost incurred for the services performed.

Leases in which a significant portion of the risks and rewards of ownership are retained by the lessor are classified as operating leases. Payments made under operating leases (net of any incentives received from the lessor) are charged to the income statement on a straight-line basis over the period of the lease.

The company leases certain laboratory equipment and office equipment. Leases for leasehold improvements and equipment where the company bears substantially all the risks and rewards of

ownership are classified as finance leases. Finance leases are capitalized at the lease’s commencement at the lower of the fair value of the leased property or the present value of the minimum lease payments.

Each finance lease payment is allocated between the liability and finance charges in order to achieve a constant rate on the finance balance outstanding. The finance balances, net of finance charges, are included in other long-term payables. The interest element of the finance cost is charged to the income statement over the lease period to produce a constant periodic rate of interest on the remaining balance of the liability for each period. The laboratory and office equipment acquired under finance leases are depreciated over the shorter of the useful life of the asset or the lease term.

Dividend distribution to the company’s shareholders shall be recognized as a liability in the company’s financial statements in the period in which the dividends are approved by the company’s shareholders.

The company’s activities expose it to a variety of financial risks: market risk (including currency risk, fair value interest rate risk, cash flow interest rate risk and price risk), credit risk and liquidity risk. The company’s overall risk management program focuses on the unpredictability of financial markets and seeks to minimize potential adverse effects on the company’s financial performance. The company uses derivative financial instruments on a limited scale to hedge certain risk exposures. No hedge accounting is applied.

Risk management is carried out by the financial management of the company. The financial management identifies, evaluates and hedges financial risks in close co-operation with the company’s operating units.

The company operates internationally and is exposed to foreign exchange risk arising from various currency exposures, primarily with respect to the British pound and the U.S. Dollar as the company receives payments from its main business partner GSK in British pounds and acquires materials produced according to good manufacturing practice for medicinal products (’GMP materials’) in US dollars. From these future commercial transactions foreign exchange risk arises. No formal policy has been set up to manage the foreign exchange risk against the functional currency of the company.

At December 31, 2012 there was a net amount of trade receivables in British pounds of € 0.6 million (2011: € 0.8 million) and a net liability in U.S. Dollars of € 0.2 million (2011: € 0.2 million). Foreign currency denominated trade receivables and trade payables are short term in nature (generally 30 to 45 days). As a result foreign exchange rate movements during the years presented had an immaterial effect on the financial statements.

The market prices for the production of preclinical and clinical compounds and drug substances as well as external contracted research may vary over time. Currently commercial product prices of the development products are uncertain. When the development products near the regulatory approval date or potential regulatory approval date, the uncertainty of the potential sales price decreases. The company is not exposed to commodity price risk.

Furthermore the company does not hold investments classified as available-for-sale or at fair value through profit or loss, therefore are not exposed to equity securities price risk.

The company’s interest rate risk arises from long-term borrowings. Borrowings issued at variable rates expose the company to cash flow interest rate risk, which is partially offset by cash held at variable rates. Borrowings issued at fixed rates expose the company to fair value interest rate risk. During 2012 and 2011, the company’s borrowings were mainly denominated in Euro’s.

The company manages its cash flow interest rate risk by using floating-to-fixed interest rate swaps. Such interest rate swaps have the economic effect of converting borrowings from floating rates to fixed rates.

At December 31, 2012 if interest rates on borrowings had been 0.1% higher/lower with all other variables held constant, post-tax results for the year would have been € 6 thousand (2011: € 4 thousand) lower/higher as a result of changes in the fair value of the borrowings. The effect of a change in interest rates of 0.1% on borrowings would have had an insignificant effect on post-tax results for the year as a result of changes in the fair value of the floating to fixed interest rate swap.

Credit risk is managed on a company basis. Credit risk arises from cash and cash equivalents as well as credit exposures to external parties, including amounts to be invoiced and outstanding receivables. For banks and financial institutions, only independently rated parties with a minimum rating of ‘A’ are accepted at the beginning of the fixed interest term.

The company does business with a limited group of external parties of which the most significant is GSK.

If external parties are independently rated, these ratings are used. If there is no independent rating, the credit quality of these parties is assessed, taking into account its financial position, past experience and other factors.

No credit limits were exceeded during the reporting period, and management does not expect any losses from non-performance by counterparties.

Management forecasts the company’s liquidity requirements to ensure it has sufficient cash to meet operational needs. Such forecasting takes into consideration the company’s financing plans and expected cash flow.

As of year-end 2012 the company had cash and cash equivalents of € 40.7 million. This in addition to expected milestone payments and cash from the collaboration with GSK will ensure the company is able to execute its operations as planned.

The table below analyses the company’s financial liabilities into relevant maturity groupings based on the remaining period at the balance sheet date to the contractual maturity date. Derivative financial liabilities are included in the analysis if their contractual maturities are essential for an understanding of the timing of the cash flows. The amounts disclosed in the table are the contractual discounted cash flows.

From inception until December 31, 2012 the company received € 5.5 million in loans from patient organizations and government agencies. Most loans have fixed redemption schemes and repayment is due when certain pre-determined milestones have been met. The company will reach these milestones on the successful commercialization of corresponding pipeline products. All such loans have been categorized as undefined.

The company’s objectives when managing capital are to safeguard the company’s ability to continue as a going concern in order to provide returns for shareholders, benefits for other stakeholders and to maintain an optimal capital structure to reduce the cost of capital.

In order to maintain or adjust the capital structure, the company may adjust the amount of dividends paid to shareholders, return capital to shareholders, issue new shares or sell assets to reduce debt.

The total amount of equity as recorded on the balance sheet is seen and managed as capital by the company.

For financial instruments that are measured in the balance sheet at fair value, IFRS 7 requires disclosure of fair value measurements by level of the following fair value measurement hierarchy:

The company’s assets and liabilities that are measured at fair value at December 31, 2012 and 2011 are all measured as level 2 financial instruments. As of December 31, 2012 and 2011 financial instruments at fair value through profit and loss amounted to € 48 thousand and € 53 thousand, respectively, and comprised of a floating to fixed interest swap (note 10).

The fair value of the anti-dilution right for Class A and B preferred shares is treated separately as an embedded derivative. The anti-dilution right is measured at nil (2011: nil).

The fair value of financial instruments that are not traded in an active market (for example, over-the-counter derivatives) is determined by using valuation techniques. These valuation techniques maximize the use of observable market data where it is available and rely as little as possible on entity specific estimates. If all significant inputs required to fair value an instrument are observable, the instrument is included in level 2.

If one or more of the significant inputs is not based on observable market data, the instrument is included in level 3.

The carrying amount of financial asset and financial liability is a reasonable approximation of the fair value and therefore information about the fair values of each class has not been disclosed.

Estimates and judgments are continually evaluated and are based on historical experience and other factors, including expectations of future events that are believed to be reasonable under the circumstances.

The company makes estimates and assumptions concerning the future. The resulting accounting estimates will, by definition, seldom equal the related actual results. The estimates and assumptions that have a significant risk of causing a material adjustment to the carrying amounts of assets and liabilities within the next financial year are addressed below.

The company has adopted an equity-settled share based compensation plan, pursuant to which the company’s directors and selected employees are granted the right to acquire depository receipts of the company (option shares). This plan is accounted for in accordance with the policy as stated in note 2.22. The total amount to be expensed is determined by reference to the fair

value of the options granted. The fair value of grants made under the Employee Share Option Plan is measured at the date of grant using a Monte-Carlo simulation model (note 16).

The company is subject to income taxes in the Netherlands. Significant judgment is required in determining the use of net operating loss carry forwards and taxation of upfront and milestone payments for income tax purposes. There are many transactions and calculations for which the ultimate tax determination is uncertain. Where the final tax outcome of these matters is different from the amounts that were initially recorded, such differences will impact the current and deferred income tax assets and liabilities in the period in which such determination is made.

Research expenditures are currently not capitalized but are reflected in the income statement because the criteria for capitalization are not met (note 4.2). At each balance sheet date, the company estimates the level of service performed by the vendors and the associated costs incurred for the services performed.

Although we do not expect the estimates to be materially different from amounts actually incurred, the understanding of the status and timing of services performed relative to the actual status and timing of services performed may vary and could result in reporting amounts that are too high or too low in any particular period.

Certain loans from patient organizations have no fixed redemption schemes and repayment is due when certain pre-determined milestones are met. Significant judgment is required in determining when the company will achieve these pre-determined milestones and these judgments may vary over time. A change in the estimate on the redemption date has an impact on the borrowing value at the balance sheet date. The borrowing value at a certain date equals the discounted value of the redemption using the effective interest rate.

The Dutch corporate income tax act provides for the possibility of a consolidated tax regime, referred to as a fiscal unity. A fiscal unity is a combination of a parent and subsidiaries whereby formally the parent, Prosensa Holding B.V., is the entity that is taxed for the consolidated profits of the fiscal unity.

The company, which has a history of recent tax losses, recognizes deferred tax assets arising from unused tax losses or tax credits only to the extent the relevant fiscal unity has sufficient taxable temporary differences or there is convincing other evidence that sufficient taxable profit will be available against which the unused tax losses or unused tax credits can be utilized by the fiscal unity. Management’s judgment is that sufficient convincing other evidence is not available and a deferred tax asset is therefore not recognized.

The project stage forms the basis for the decision whether costs incurred for the company’s research and development projects can be capitalized or not. In general, the company’s vision is

that clinical development expenditures are not capitalized until the company files for regulatory approval (i.e. approval to commercially use the product; for example the filing for final FDA approval in the United States or filing for market authorization with the EMA in the EU), as this is considered to be essentially the first point in time where it becomes probable that future revenues can be generated and the project becomes commercially successful.

As of each balance sheet date, the company estimates the level of service performed by the vendors and the associated costs incurred for the services performed. As part of the process of preparing the company’s financial statements the company is required to estimate its accrued expenses. This process involves reviewing quotations and contracts, identifying services that have been performed on the company’s behalf, estimating the level of service performed and the associated cost incurred for the service when it has not yet been invoiced or otherwise notified of the actual cost. The majority of the company’s service providers invoice it monthly in arrears for services performed or when contractual milestones are met. The company makes estimates of its accrued expenses as of each balance sheet date in its financial statements based on facts and circumstances known to it at that time. The company periodically confirms the accuracy of its estimates with the service providers and makes adjustments if necessary. The significant estimates in its accrued research and development expenses are related to fees paid to clinical research organizations, or CROs, in connection with research and development activities for which the company has not yet been invoiced. The company bases its expenses related to CROs on its estimates of the services received and efforts expended pursuant to quotes and contracts with CROs that conduct research and development on its behalf.

The financial terms of these agreements are subject to negotiation, vary from contract to contract and may result in uneven payment flows. There may be instances in which payments made to vendors will exceed the level of services provided and result in a prepayment of the research and development expense. In accruing service fees, the company estimates the time period over which services will be performed and the level of effort to be expended in each period. If the actual timing of the performance of services or the level of effort varies from the company’s estimate, it adjusts the accrual or prepayment expense accordingly. Although the company does not expect its estimates to be materially different from amounts actually incurred, its understanding of the status and timing of services performed relative to the actual status and timing of services performed may vary and could result in reporting amounts that are too high or too low in any particular period.

In October 2009 the company signed a Research & Development and Collaboration & License agreement with GSK. Upon signing of the agreement the company received € 17.2 million (GBP 16.0 million) as a non-refundable upfront payment. As the company has continuing performance obligations revenues related to the license fee payments are deferred and the related revenues are recognized in the period of the expected performance. The company has made the assumption that the expected performance occurs on a straight line basis over the 5 year period the company is obliged to provide research and development services regarding certain pre-defined programs in the agreement.

Other upfront license fee payments are deferred and revenue is recognized based on the percentage of completion method. Use of the percentage of completion method requires the company to estimate the work performed to date as a proportion of the total work to be performed.

Depreciation expense of € 757 thousand (2011: € 801 thousand) has been charged to research and development expense. Depreciation expense of € 175 thousand (2011: € 53 thousand) has been charged to general and administrative expense.

Lease rentals amounting to € 721 thousand (2011: € 662 thousand) and € 30 thousand (2011: € 41 thousand) relating to the lease of buildings and office equipment, respectively, are included in the income statement (note 22 and 23).

The company leases various laboratory equipment and office equipment under non-cancellable finance lease agreements. The lease terms are between 3 and 5 years.

Laboratory equipment includes the following amounts where the company is a lessee under a finance lease:

Office equipment includes the following amounts where the company is a lessee under a finance lease:

Amortization expense of € 139 thousand (2011: € 111 thousand) has been charged to research and development expense. Amortization expense of € 94 thousand (2011: € 95 thousand) has been charged to general and administrative expense.

The remaining amortization period of patent and licenses is approximately 6.5 years and 1-3 years for capitalized software.

The credit quality of financial assets that are neither past due nor impaired can be assessed by reference to external credit ratings (if available) or by historical information about counterparty default rates:

None of the financial assets that are fully performing have been renegotiated in the last year.

The notional principal amount of the outstanding interest rate swap contract at December 31, 2012 was € 500 thousand (2011: € 600 thousand).

At December 31, 2012 the fixed interest rate was 4.15% (2011: 4.15%), and the floating rate was Euribor plus 1.75% (2011: Euribor plus 1.75%).

Gains and losses from changes in the fair value of interest rate swap contracts are recorded through profit and loss.

Class A and B shareholders are equipped with an anti-dilution right, in case the company issues additional shares, options or securities below the shareholders’ acquisition price and certain pre-defined criteria are met. The anti-dilution option is a financial instrument and had an insignificant value as of December 31, 2012 and 2011.

In August 2012 the company settled a long term loan receivable from 2009 with outstanding payables of the related supplier. The restricted cash balance secures a bank loan.

As of December 31, 2012 the company valued finished goods of GMP materials to supply clinical centers at nil (2011: nil) due to the uncertainty that future economic benefit will flow to the company from the use of the inventories. As of December 31, 2012 these inventories represent a value at cost of € 2.7 million (2011: € 2.3 million).

The fair value of trade and other receivables approximates their carrying value. As of December 31, 2012 and 2011, no trade or other receivables were impaired or not performing. The carrying amount of the company’s trade receivables are approximately 61% denominated in British pounds, while other receivables are fully denominated in Euro’s.

In 2006 the company received a bank loan of € 900 thousand from ABN Amro N.V. An amount of € 500 thousand secures the bank loan, and is therefore considered restricted cash and recorded as a component of other financial assets. The remaining balance is at the free disposal of the company.

On January 16, 2012 the company concluded an agreement for new equity financing led by a new investor, New Enterprise Associates (NEA), and supported by existing Prosensa investors: Abingworth, Life Sciences Partners, Gimv, Idinvest Partners and MedSciences Capital. As a result of this agreement the company has issued 9,107,144 class B shares with total net proceeds of €22.7 million.

The total authorized number of ordinary shares is 21 million shares (2011: 21 million shares) with a par value of € 0.01 per share (2011: € 0.01 per share). All issued shares are fully paid.

Besides the minimum amount of share capital to be held under Dutch law, there are no distribution restrictions applicable to equity of the company.

Class A, Class B and Class O shares have a dividend preference over ordinary shares. Class B shares have a dividend preference over Class A and Class O. Class A have a dividend preference over Class O shares. The Class A, Class B and Class O have a dividend preference of 8%, 8% and 6% respectively. The dividend preference is non-cumulative. According to the statutory regulations of the company the general meeting of shareholders can decide to make a profit distribution.

Class A and Class B shares have an anti-dilution protection that is not applicable for Class O and ordinary Shares resulting in Class A and Class B shares being split in an equity part and a liability part at inception of the instrument. The anti-dilution option is measured at nil as of December 31, 2012 and 2011.

The company has adopted a share-based compensation plan, pursuant to which the company’s directors and selected employees are granted the right to acquire depository receipts of the company (option shares) (note 16). The share-based payment expenses are recorded in the income statement. The share based compensation plan is equity-settled. In case of an equity settled plan, there is no obligation to transfer economic benefits, therefore the credit entry should be recognized as an increase in equity. The company uses Other reserves as the equity classification.

Foundation Prosensa Trust Office (Stichting Administratiekantoor Prosensa Holding B.V.)

The Foundation Prosensa Trust Office (‘Stichting Administratiekantoor Prosensa Holding B.V.’ or ‘foundation’) is a trust office with a board independent of the company.

Upon the exercise of an option right, ordinary shares are issued to the foundation, whose purpose is to facilitate administration of options and pool the voting interests of the underlying shares. The foundation then grants a depository receipt for each issued ordinary share to the person exercising his or her option right. The depositary receipt holder is entitled to any dividends or other distributions paid on the ordinary shares for which the depositary receipts are granted. The voting rights and other rights attached to the ordinary shares are exercised by the foundation. The depositary receipt holders are not entitled to attend a general meeting of shareholders or to cast a vote. The voting rights attached to the ordinary shares are exercised by the foundation at its own discretion.

Board members of the foundation are appointed by the supervisory board. The board consists of at least three board members. Currently one board member is appointed on the binding nomination of the joint meeting of holders of Class A and Class B preferred shares. A second board member is appointed on the binding nomination of the general meeting of shareholders. The third board member is an employee.

The company has adopted share-based compensation plans, pursuant to which the company’s directors and selected employees are granted the right to acquire depository receipts issued over ordinary shares of the company by the foundation (option shares). The share-based compensation plans are equity-settled. Legal title to the shares issued under the share-based

compensation plan is held by the foundation. In the event such right is exercised the company issues ordinary shares to the foundation which issues non-voting depository receipts in the same quantities to the respective directors or selected employees.

Options are generally conditional on the employee completing a four year period of service (the vesting conditions). Each such option award vests based on the following schedule: (a) 25% on the first anniversary of the date of the grant, provided that on that date the relevant director or selected employee is still employed by the company, and (b) the remaining 75% in 36 equal monthly installments over a three year period following the first anniversary of the date of grant subject to continued employment of the relevant employee. The company may decide to accelerate the vesting of the options as a result of a change of control.

On December 5, 2012 the company granted to the members of the Management Board 1.0 million options that vest only upon a liquidity event such as a change of control of the company or an IPO, subject to the continued employment of the member of the Management Board. In the event of an IPO, the number of options eligible to vest is reduced from 1.0 million to 800,000. In order for any options to become subject to vesting, the proceeds from a liquidity event or in the case of an IPO, the sustained closing market price for the ordinary shares during any 20 consecutive trading days outside a lock-up or blackout period must exceed a threshold share price. The number of options subject to vesting increases between the threshold share price and the share price entitling the participant to exercise the maximum number of options. Upon each subsequent achievement of a sustained, higher closing market price or level of proceeds from a liquidity event, an additional number of options will become subject to vesting. Each option grant subject to vesting in the event of an initial public offering will vest and become exercisable based on the following schedule: 25% of the options subject to vesting will vest the day immediately following attainment of such pricing levels (the initial vesting date), and an additional 2.083% will vest at the end of each successive one month period following the initial vesting date, subject to the continued employment of the relevant member of the management board. Upon a change of control all options subject to vesting under this grant will immediately vest based on the price level of the total proceeds per share.

Unless forfeited or exercised on an earlier date the options expire 10 years after the grant date.

Movements in the number of share options outstanding and their related weighted average exercise prices are as follows:

Out of the 2,207,707 options outstanding (2011:1,418,232), 604,252 options (2011:342,872) were exercisable.

In 2012 and 2011 there was one opportunity to exercise options. The estimated fair value of the ordinary shares at the moment of exercise amounted to € 0.70 in 2012 and € 1.00 in 2011.

During 2011 the exercise price of 519,350 options was changed to € 0.01 to align the exercise price to the 2010 plan. The incremental fair value granted amounts to € 410 thousand and is the difference between the fair value of the options with revised exercise price (€ 0.01) versus the fair value of the options with the original exercise price, both estimated as at the date of the modification. From the modification date this incremental fair value is recognized as an expense over the remainder of the vesting period in addition to the expense recognized for the original fair value of the options.

Options outstanding at the end of the year have the following weighted average remaining contractual lifes and ranges of exercise prices:

The fair value of stock options under the various grants is based on a Monte-Carlo simulation using the following assumptions:

In respect of the 1.0 million options granted to members of the Management Board in 2012 that vest only upon a liquidity event such as a change of control of the company or an IPO, the actual number of options subject to vesting will depend on the value of the company’s shares in the change of control transaction or the share price development following an IPO. This market performance condition is included in the fair value of the options granted. As of December 31, 2012, the requirements subject to the vesting of these options are deemed not probable under an IPO scenario, and amounts are de minimus under a change of control scenario and therefore no expenses have been recognized. Until the date an IPO is considered to be probable, no expense will be recognized for these grants. The total expense to be recognized under an IPO scenario approximates €1.3 million.

The fair value of the ordinary shares is determined by the Management Board and Supervisory Board, and takes into account the most recently available valuation of ordinary shares performed by an independent valuation firm and the assessment of additional objective and subjective factors the company believes are relevant and which may have changed from the date of the most recent valuation through the date of the grant.

The management board and supervisory board consider numerous objective and subjective factors to determine their best estimate of the fair value of the ordinary shares as of each grant date, including the following:

In determining the fair values of the ordinary shares as of each award grant date, three generally accepted approaches were considered: income approach, market approach and cost approach. Based on the stage of development and information available, the company has determined that the income approach is the most appropriate method, and when applicable, the company has also employed the prior sale of company stock method to estimate the aggregate enterprise value. In addition, the company has taken into consideration the guidance prescribed by the American Institute of Certified Public Accounts (AICPA) Audit and Accounting Practice Aid, Valuation of Privately-Held-Company Equity Securities Issued as Compensation.

converted to present value by means of discounting, using a rate of return that accounts for the time value of money and the appropriate degree of risks inherent in the business. The discount rate in the DCF analysis is based upon a weighted average cost of capital (WACC) calculated at each valuation date. The WACC is a method that market participants commonly used to price securities and is derived by using the Capital Asset Pricing Model and inputs such as the risk-free rate, beta coefficient, equity risk premiums and the size of the company.

The indicated fair value calculated at each valuation date is allocated to the preferred shares and ordinary shares using the current value method (CVM) and option pricing method (OPM). The CVM assumes an immediate exit of the company and allocates value to the preferred shares based on the liquidation preferences or conversion values, whichever would be greater, and the residual value to the ordinary shares. The OPM treats ordinary shares and preferred shares as call options on the total equity value of a company, with exercise prices based on the value thresholds at which the allocation among the various holders of a company’s securities changes. Under this method, the ordinary shares have value only if the funds available for distribution to shareholders exceed the value of the liquidation preference at the time of a liquidity event, such as a strategic sale, assuming the enterprise has funds available to make a liquidation preference meaningful and collectible by the holders of preferred shares. The ordinary shares are modeled as a call option on the underlying equity value at a predetermined exercise price. In the model, the exercise price is based on a comparison with the total equity value rather than, as in the case of a regular call option, a comparison with a per share price. Thus, ordinary shares are considered to be a call option with a claim on the enterprise at an exercise price equal to the remaining value immediately after the preferred shares are liquidated. The OPM uses the Black Scholes option-pricing model to price the call options. This model defines the securities’ fair values as functions of the current fair value of a company and uses assumptions such as the anticipated timing of a potential liquidity event and the estimated volatility of the equity securities. Volatility has been estimated based on the observed daily share price returns of peer companies over a historic period equal to the period for which expected volatility is estimated. Volatility is defined as the annualized standard deviation of share price returns. In the allocation of equity, the company has also considered valuation outcomes of ordinary shares through a sale of the company versus an IPO and considered the probabilities of each at each valuation date, since the treatment of the liquidation rights is different for these two events. The aggregate value of the ordinary shares is then divided by the number of ordinary shares outstanding to arrive at the per share value.

significant results in 2011 from any of our development programs including the Phase III-DMD114044 pivotal trial initiated in December 2010, the continuation of the dose escalation study of PRO044 and the preclinical safety studies for PRO045 and PRO053 on-going throughout 2011. Additional valuations were performed by an independent valuation firm as of September 30, 2012 and December 5, 2012 for share-based compensation grants in 2012.

The ordinary shares valuation as of December 2010 relied on a DCF to derive the total enterprise value. The cash flow projections were based on probability-weighted scenarios which considered estimates of time to market of the products, market share and pricing. The cash flow projections were estimated over a period equal to the expected product life cycle, and a terminal value period was not applied. All DMD indications in development were included in estimating cash flow projections, most importantly drisapersen. The expected sales were estimated based on a regional level, estimated patient populations and market shares. Production and research and development costs were estimated at the indication level with general and administrative costs and selling and marketing costs assessed at the overall company level. Cash flow projections also incorporated expected royalties and milestones related to the collaboration agreement with GSK. A WACC of 16.0% was applied. Equity was allocated using the CVM and, applied retrospectively, an OPM, resulting in a determination by the Supervisory Board and the Management Board of a value per ordinary share of €1.00. The CVM and OPM rely on the anticipated timing and probability of a liquidity event based on then current plans and estimates of the Supervisory Board and Management Board regarding a liquidity event of 80-85% probability of a sale of the company and 15-20% probability of an IPO. The company assumed volatility of 60% based on historical trading volatility for the publicly traded peer companies and a time to liquidity of 1.5 years.

In December 2010, the Phase III-DMD114044 pivotal trial was initiated by GSK, and results are currently expected to be available in the fourth quarter of 2013. The completion of this trial will be later than anticipated in the projections that were used for the valuation performed in 2010. In 2011 the company also concluded an amendment to the GSK agreement related to the development terms for PRO044. In this amendment the timing of the milestone payment for GSK licensing PRO044, which had been anticipated in the second quarter of 2011, was restructured, and the anticipated licensing to GSK of PRO044 was deferred significantly. In January 2012, the company raised total net proceeds of € 22.7 million in a private placement of the preferred (Class B) shares. The additional Class B shares were issued on a pari passu basis to the original Class B shares issued in December 2008 with a liquidation preference senior to Class A, Class O and ordinary shares. The events above in the aggregate had a downward effect on the valuation of the ordinary shares as of the end of 2011 and in 2012.

The ordinary shares valuation as of September 30, 2012 and December 5, 2012 relied on a DCF as well as the prior sale of company stock method in connection with the January 2012 financing round to derive the total enterprise value. There were no events between the respective valuation dates and therefore the analyses and inputs remained the same. The cash flow projections were based on probability-weighted scenarios which considered estimates of time to market of the products, market share and pricing. Projections were updated from the December 2010 valuation for anticipated timing of placebo-controlled clinical trial results, the progress since the last valuation date and the development of a competing drug for DMD that increased the risk of the losing a first-mover advantage. A WACC of 15.5% was applied. Under the prior sale of company stock method, the company used the implied value from the latest financing round in January 2012 and an estimated annualized return on equity over the period

between the financing round and the valuation date for the valuation of the enterprise value as of September 30, 2012 considering the factors noted above. Equity was allocated using the CVM and OPM, resulting in a value per ordinary share of € 0.70. The CVM and OPM rely on the anticipated timing and probability of a liquidity event based on then current plans and estimates of the supervisory board and management board regarding a liquidity event of 80-85% probability of the sale of the company and 15-20% probability of an IPO. The company assumed volatility of 60% based on historical trading volatility for the publicly traded peer companies and a time to liquidity of 0.50 years.

The company expects all vested options to be exercised. Therefore the company considers the expected life of the options to be in line with the vesting period of the options.

The company has historically been a private company and lacks company-specific historical and implied volatility information. Therefore, the company estimates the expected volatility based on the historical volatility of the publicly traded peer companies as indicated above and has been set at 60%.

See note 24 for the total expense recognized in the income statement for share options and other share-based payment granted to directors and selected employees. Share options are accounted for as a contribution to equity and separately accounted for as other reserves.

In 2011 and 2012, the company made, as part of the share-based compensation plan, awards entitling recipients to acquire Depositary Receipts (Restricted Shares) against payment of the nominal value of the underlying ordinary shares (the Purchase Price), subject to the right to repurchase all or part of such Depositary Receipts at the lower of the Purchase Price and the fair value of the ordinary shares during the four year vesting period if the participant ceases to perform services to the company. The company has the right to repurchase 100% of the Restricted Shares awarded, and this right to repurchase shares will be reduced based on the following schedule: (a) 25% on a date of the year following the vesting commencement date no later than the anniversary of the grant, and (b) the remaining 75% in 36 equal monthly installments over a three year period following the first anniversary of the first vesting date.

During 2012, the company issued 115,000 Restricted Shares (2011: 89,750) with a vesting period up to 4 years. The fair value of the Restricted Shares granted in 2012 of € 0.70 (2011: € 1.00) was measured based on the estimated fair value of the ordinary shares at the moment of purchase the depository receipts, which amounts to € 0.70 in 2012 and € 1.00 in 2011 in line with the valuations of the ordinary shares. The company is not in a financial position to pay dividends in the foreseeable future. Therefore dividend payments have not been considered in the valuation of the restricted share awards.

The share-based payment expense related to the Restricted Shares amount to € 18 thousand in 2012 and € 45 thousand in 2011, which is included in the total share-based payment expense for the year disclosed (note 24).

The company granted option rights to two employees of the company to purchase a total of 123,750 ordinary shares owned by the shareholder at a price of €1.82 per ordinary share. The option rights are unconditional and can be exercised for ten years from the grant date. The outstanding options of 33,750 as of December 31, 2012 and 2011 are held by one single employee. The other employee exercised the options in previous years.

The weighted average remaining contractual life of the outstanding options was 5 and 6 years as of December 31, 2012 and 2011, respectively.

Movements in the number of call option rights outstanding and their related weighted average exercise prices are as follows:

Compensation of the Management Board and the Supervisory Board including share-based payment are described in note 31.

Other liabilities mainly consist of accruals for services provided by vendors but not yet billed, reimbursements received from research and development partners for expenses which have yet to be incurred and miscellaneous liabilities.

In 2008 Prosensa and Leiden Universitair Medisch Centrum (LUMC) extended and amended a research and license agreement with respect to commercialization of therapeutic products based on LUMC intellectual property rights and the joint technologies. Under this agreement the company is obliged to make milestone and royalty payments to LUMC, depending on the progress of the development of the joint technologies. In relation to this agreement as of December 31, 2012 and 2011 no amounts were outstanding.

In 2006 the company received a bank loan of € 900 thousand from ABN Amro N.V. which matures in 2017. The loan bears interest equal to Euribor plus 1.75% per year. The company redeems an amount of € 25 thousand per quarter. The current portion of € 100 thousand is included in borrowings—current portion. There is no portion of the loan exceeding five years. The company has a credit facility with an undrawn balance of € 254 thousand (2011: € 300 thousand). The total amount of the credit facility available to the company decreases by € 46 thousand per annum.

The company has obtained other loans from various governmental and non-profit groups. To encourage research and development the company obtained certain loans that generally bear an interest rate below the market interest rate, considered by the company to be 12% over the last years. The difference between fair value and the notional amount at inception is treated as a donation received for certain research performed by the company. These borrowings were initially recognized at fair value at inception with the difference between the fair value and the notional amount recognized as other income in the statement of comprehensive income.

There is no exposure for the company’s other borrowings to interest rate changes and contractual repricing. Interest rates are fixed until maturity. The fair values of the non-current borrowings approximate their carrying values. The fair value of current borrowings equals their carrying amount, as the impact of discounting is deemed immaterial. The carrying amounts of the company’s borrowings are denominated in Euro’s.

The principal amount of the loan is € 65 thousand and was received on October 10, 2005. The loan bears a below market interest rate. No fixed redemption scheme was agreed on. The loan shall be repaid in the first year after the company reaches a pre-defined milestone. The loan is not secured.

On December 22, 2005 a loan of € 70 thousand was granted. In 2006 an additional loan amount of € 70 thousand was received. The loans shall be repaid with fixed terms when the company obtains regulatory approval to bring the first product candidate to the market. The loans are interest free and are not secured.

In 2012 the company received from Association Française contre les Myopathies € 3.0 million related to a funding agreement for research and development in two separate installments on April 12, 2012 and December 21, 2012. The loans shall be repaid with fixed terms when the company meets a revenue target on the product candidates PRO044, PRO045 and PRO053.

The AFM agreement gives us the option to terminate the agreement if we undergo a change of control. If we exercise our option to terminate the agreement, we are required to repay the loan, together with interest. In the event that we abandon the program for reasons not justified by a scientific or medical reason, we are similarly required to repay the loan, together with interest.

The AFM agreement also requires us to grant to AFM a non-exclusive royalty-free license to the intellectual property covered by the agreement in the event that we abandon the research funded by the agreement.

This loan of € 500 thousand was received in two tranches, € 300 thousand on July 14, 2006 and € 200 thousand on October 10, 2006. The loan bears a below market interest rate that accumulates to the principal amount. No fixed redemption scheme was agreed on. The loan shall

be repaid with fixed terms after the company obtains regulatory approval to bring the first product candidate to the market. The loan is not secured.

On May 9, 2006 a loan of € 100 thousand was granted that was received in two tranches in 2006. In 2008 an additional amount of € 63 thousand was received. No interest is charged and no fixed redemption scheme was agreed. The loan shall be repaid after the company obtains regulatory approval to bring the first product candidate to the market. The loan is not secured.

The (subordinated) loan of € 250 thousand was received on December 22, 2006 and bears a below market interest rate. No fixed redemption scheme was agreed. In 2012 we received € 165 thousand and in 2011 we received € 475 thousand. The loan as well as an additional payment of € 250 thousand shall be repaid with fixed terms after the company obtains regulatory approval to bring the first product candidate to the market. In case of a liquidation event of the company (e.g. change of control of the company), the loan converts to ordinary shares with a maximum value of the loan amount, accumulated interest and an additional €250 thousand. The loan is not secured.

During 2012 and 2011, the company received loan installments from Agentschap NL for a total amount of € 640 thousand which bears an interest rate of 9.5% per annum. In 2012 we received €165 thousand and in 2011 we received €475 thousand. The granted loan is an innovation credit facility (Innovatiekrediet) of the Dutch Ministry of Economic Affairs. The company has pledged the part of its materials and immaterial fixed assets that directly relate to the project funded by the loan granted.

On September 27, 2012 the company received from Everest International Pte Ltd € 300 thousand as an installment of a € 1.0 million funding agreement for research and development. No fixed redemption scheme was agreed on. The loan shall be repaid with fixed terms when preclinical product candidates meet commercial milestones. The loan is not secured.

In 2012 the company received from Charley’s Fund $ 500 thousand (€387 thousand) as installment of a $ 1.5 million funding agreement for research and development which bears an interest rate that approximates the market interest rate. No fixed redemption scheme was agreed on. The loan shall be repaid in installments with fixed terms when certain clinical and regulatory milestones are met. The loan is not secured.

Finance lease liabilities are effectively secured as the rights to the leased asset revert to the lessor in the event of default. The carrying amount corresponds to the fair value as terms of the contracts were agreed at arm’s length and market conditions for such contracts have not changed since. The interest rate imposed by the lessor for all finance lease liabilities is 8% per annum.

Revenues to date have consisted principally of license revenue and collaboration revenue. The group generates both license revenue and collaboration revenue under the GSK Agreement.

In 2009, the company entered into the GSK Agreement for the development and commercialization of RNA-based therapeutics for DMD. Pursuant to the GSK Agreement, the company granted GSK an exclusive worldwide license to develop and commercialize the lead compound, drisapersen. The company has also granted GSK an option to receive an exclusive worldwide license for the second lead compound, PRO044. In addition, GSK has the option to obtain an exclusive worldwide license for either PRO045 or PRO053, and an option to obtain an exclusive worldwide license for either PRO052 or PRO055. PRO045 is paired with PRO053, and PRO052 is paired with PRO055, because each of the product candidates in the respective pairings addresses a patient sub-population of a similar size and is at a comparable stage of development. Since 2009, the company has received €47.4 million under the GSK Agreement and recognized revenue totaling €27.2 million of license revenue over the full period of the agreement until December 31, 2012. All payments by GSK are made in British pounds.

In October 2009 the company signed a Research & Development and Collaboration & License agreement with GSK. Upon signing of the agreement the company received GBP 16 million (€ 17.2 million) as a non-refundable upfront payment. The upfront fee relates to all compounds included in the agreement. Milestones relate to the individual projects (e.g. PRO045 / PRO053). The expected performance occurs on a straight line basis over the five year period. At initiation of the contract, the company determined to recognize the payment ratably over a period of five years which equals the minimum research term both parties committed to under the agreement. As the agreement is still in place, the company still considers the contractual term to be the accurate term for deferring revenue.

The company receives upfront payments to fund research and development activities until GSK exercises its option for a particular compound. The upfront payments are recognized by reference to the stage of completion of the underlying agreement at the balance sheet date (also referred to as percentage of completion method) due to the fact that the rendering of services under the license revenue agreement can be estimated reliably.

Use of the percentage of completion method requires the group to estimate the work performed to date as a proportion of the total work to be performed. The company updates the cost to complete to determine the percentage of completion at least on a quarterly basis. In 2012, the group released to revenue € 2.3 million (2011: € 3.1 million) related to the upfront payments for the PRO045 / PRO053 program and the PRO052 / PRO055 program.

In June 2012, the company received a GBP 5.0 million (€ 6.2 million) advance option payment under the GSK collaboration agreement. The advance option payment was deferred and will be recognized in revenue when the payment becomes unconditional. The payment will become unconditional at the time that GSK exercises its option to the related compound.

Collaboration revenue from contracts, typically from delivering research and development services, which may or may not be related to the licensing agreement, is recognized on the basis of labor hours delivered at the contractual full time employee rates. Under the agreement an additional amount of € 2.1 million (2011: € 2.2 million) was recognized as collaboration revenue from delivering research and development services for studies to GSK.

Other income of € 174 thousand (2011: € 36 thousand) includes € 4 thousand income from government grants and € 170 thousand from a donation received for research activities. To encourage research and development the company obtained certain loans that generally bear interest at a rate below the market interest rate, considered by the company to be 12% over the last four years. The difference between fair value and the notional amount at inception is treated as a donation received for certain research performed by the company.

Foreign exchange gains relate largely to transactions with GSK denominated in British pounds.

No tax charge or income has been recognized in the years 2012 and 2011 since the company is in a loss-making position and has a history of losses. Thus, no deferred tax asset has been recognized for carry-forward losses (note 4).

The company has tax loss carry-forwards of approximately € 42.1 million (2011: € 32.2 million). An amount of € 4.7 million relates to the pre-fiscal unity of the Prosensa Holding B.V. As a result of the Dutch income tax law, tax loss carry-forwards are subject to a time limitation of nine years. Tax loss carry-forwards incurred in prior years will expire as follows:

Deferred income tax assets are recognized for tax losses and other temporary differences to the extent that the realization of the related tax benefit through future taxable profits is probable. Deferred tax assets and liabilities are offset if they pertain to future tax effects for the same taxable entity towards the same taxation authority.

No income taxes were paid and no deferred income tax was expensed or recognized through the income statement in the years ended December 31, 2012 and 2011. Losses are attributable to operations in the Netherlands.

As the company’s temporary differences between tax gains / losses and current gains / losses, if any, are deemed immaterial and their realization is uncertain the company refrains from further disclosures.

In order to promote innovative technology development activities and investments in new technologies, a corporate income tax incentive has been introduced in Dutch tax law called the Innovations Box. For the qualifying profits, the company effectively owes only 5% income tax, instead of the general tax rate of 25.5% which results in an estimated effective tax rate of 10%. The agreement with the tax authorities is currently signed for the years 2011 – 2015 but expected to be extended.

Basic loss per share is calculated by dividing the loss attributable to equity holders of the company by the weighted average number of ordinary and preferred shares in issue during the year.

The company did not declare dividends for the years ended December 31, 2012 and 2011.

The company leases office space and laboratory space under non-cancellable operating lease agreements. The lease term is between 1 and 5 years.

Furthermore the company entered into several lease agreements for office equipment. The annual obligations amount to € 14 thousand (2011: € 41 thousand). The lease obligations term is between 1 and 3 years.

The lease expenditure charged to the income statement during the year amounted to € 751 thousand (2011: € 703 thousand). The future aggregate minimum lease payments under non-cancellable operating leases are as follows:

In 2011 the company secured the fulfillment of the terms and conditions of an operational lease agreement through a bank guarantee to the lessor for an amount of € 18 thousand. The guarantee was released in 2012.

In 2012 the company received a loan from Agentschap NL for a total amount of € 640 thousand which bears an interest rate of 9.5% per annum. The company has pledged the part of its materials and immaterial fixed assets that directly relate to the project funded by the loan granted.

The Supervisory Board members were paid € 7 thousand and € 4 thousand for consulting services during the years ended December 31, 2012 and 2011, respectively. The services were rendered at arm’s length.

In 2012 and 2011 the Management Board was paid a total of € 1.6 million and € 1.1 million, respectively, in salaries as well as short term benefits. In 2012 the Management Board members received bonus payments in March related to 2011 and in December related to 2012. € 160 thousand and € 557 thousand, respectively, was expensed for share-based payment awards. Contributions to post employment schemes amounted to € 161 thousand and € 140 thousand during the years ended December 31, 2012 and 2011, respectively. No termination benefits or other long term benefits were paid. The Management Board held 1,759 thousand and 969 thousand stock options as of December 31, 2012 and 2011, respectively. In addition, the Management Board held 149 thousand restricted shares and 472 thousand other depositary receipts issued by the Foundation.

On December 5, 2012 the Management Board were granted 1.0 million stock options that vest subject to a liquidity event and continued employment. As of December 31, 2012 the requirements to vest were deemed not probable under an IPO Scenario, and de minimus under a change of control scenario, and therefore no expenses were recognized in the income statement.

Selected members of the Supervisory Board were paid in total an amount of € 50 thousand during the years ended December 31, 2012 and 2011. In 2012 two members of the Supervisory Board were granted 15,000 Restricted Shares and 11,250 Options with an exercise price of € 0.01(2011: 30,000 Restricted Shares and 42,500 Options with an exercise price of € 0.01). The Options and Restricted Shares were granted under the company’s share based compensation plan (note 16).

No loans, advances and guarantees were made to the Management Board and Supervisory Board members as of December 31, 2012 and 2011.

The auditors PricewaterhouseCoopers Accountants N.V. have performed the following services for the company:

No events occurred after the balance sheet date that would have a material impact on the result or financial position the company.

No action is being taken in any jurisdiction outside the United States to permit a public offering of the ordinary shares or possession or distribution of this prospectus in that jurisdiction. Persons who come into possession of this prospectus in jurisdictions outside the United States are required to inform themselves about and to observe any restrictions as to this offering and the distribution of this prospectus applicable to that jurisdiction.

Until , 2013, all dealers that buy, sell or trade in our ordinary shares, whether or not participating in this offering, may be required to deliver a prospectus. This is in addition to the dealers’ obligation to deliver a prospectus when acting as underwriters and with respect to their unsold allotments or subscriptions.

Members of our management board and supervisory board have the benefit of the following indemnification provisions in our Articles of Association:

Current and former management directors and supervisory directors shall be reimbursed for:

There shall be no entitlement to reimbursement as referred to above if and to the extent that:

If and to the extent that it has been established by a Dutch court or, in the event of arbitration, an arbitrator in a final and conclusive decision that the person concerned is not entitled to reimbursement as referred to above, he shall immediately repay the amount reimbursed by the Company.

We also intend to enter into indemnification agreements with each of our management directors and supervisory directors upon the consummation of this offering.

Reference is made to Section 7 of the Form of Underwriting Agreement filed as Exhibit 1.1 to the registration statement which sets forth the registrant’s and the underwriters respective agreements to indemnify each other and to provide contribution in circumstances where indemnification is unavailable.

In January 2012, we issued and sold (i) an aggregate of 5,000,004 of our Class B2 shares at a price per share of €2.30 for an aggregate purchase price of €11,500,009.20 and (ii) an aggregate of 4,107,140 of our Class B3 shares at a price per share of €2.80 for an aggregate purchase price of €11,499,992. All outstanding shares of our Class B2 and Class B3 shares will automatically convert into 9,107,144 ordinary shares upon the completion of this offering.

The Class B2 Shares and Class B3 Shares were issued and sold in reliance upon the exemption from registration under Section 4(2) of the Securities Act. We have used the proceeds from this offering for research and development and general corporate purposes.

The table below summarizes our options issued within the past three years. The grant of the options and the issuance of ordinary shares upon the exercise of options described in the table below were or will be made pursuant to Regulation S under the Securities Act or Section 4(2) of the Securities Act.

The table below summarizes our restricted shares issued within the past three years. The grants of the restricted shares described in the table below were made pursuant to Regulation S under the Securities Act or Section 4(2) of the Securities Act.

(a) The undersigned registrant hereby undertakes to provide to the underwriter at the closing specified in the underwriting agreements, certificates in such denominations and registered in such names as required by the underwriter to permit prompt delivery to each purchaser.

(b) Insofar as indemnification for liabilities arising under the Securities Act of 1933 may be permitted to directors, officers and controlling persons of the registrant pursuant to the foregoing provisions, or otherwise, the registrant has been advised that in the opinion of the U.S. Securities and Exchange Commission such indemnification is against public policy as expressed in the Act and is, therefore, unenforceable. In the event that a claim for indemnification against such liabilities (other than the payment by the registrant of expenses incurred or paid by a director, officer, or controlling person of the registrant in the successful defense of any action, suit or proceeding) is asserted by such director, officer or controlling person in connection with the securities being registered, the registrant will, unless in the opinion of its counsel the matter has been settled by controlling precedent, submit to a court of appropriate jurisdiction the question of whether such indemnification by it is against public policy as expressed in the Act and will be governed by the final adjudication of such issue.

(1) For purposes of determining any liability under the Securities Act of 1933, the information omitted from the form of prospectus filed as part of this registration statement in reliance upon Rule 430A and contained in a form of prospectus filed by the Registrant pursuant to Rule 424(b)(1) or (4) or 497(h) under the Securities Act shall be deemed to be part of this registration statement as of the time it was declared effective.

(2) For the purpose of determining any liability under the Securities Act of 1933, each post-effective amendment that contains a form of prospectus shall be deemed to be a new registration statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

Pursuant to the requirements of the Securities Act of 1933, the registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form F-1 and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in Leiden, the Netherlands on May 24, 2013.

KNOW ALL PERSONS BY THESE PRESENTS, that each person whose signature appears below hereby constitutes and appoints Hans G.C.P. Schikan and Berndt A.E. Modig and each of them, individually, as his true and lawful attorneys-in-fact and agents, with full power of substitution and resubstitution, for him and in his name, place and stead in any and all capacities, in connection with this registration statement, including to sign in the name and on behalf of the undersigned, this registration statement and any and all amendments thereto, including post-effective amendments and registrations filed pursuant to Rule 462 under the U.S. Securities Act of 1933, and to file the same, with all exhibits thereto, and other documents in connection therewith, with the U.S. Securities and Exchange Commission, granting unto such attorneys-in-fact and agents full power and authority to do and perform each and every act and thing requisite and necessary to be done in and about the premises, as fully to all intents and purposes as he might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents, or his substitute, may lawfully do or cause to be done by virtue hereof.

Pursuant to the requirements of the Securities Act of 1933, as amended, this registration statement has been signed by the following persons on May 24, 2013 in the capacities indicated:



Title of each Class of Securities to be Registered	Proposed Maximum Aggregate Offering Price⁽¹⁾	Amount of Registration Fee
Ordinary shares, nominal value €0.01 per share	$60,000,000	$8,184


	Per share	Total

Initial public offering price	$	$

Underwriting discounts and commissions	$	$

Proceeds to us, before expenses	$	$


	$		€

Net tangible book value per share at March 31, 2013
Increase in net tangible book value per share attributable to new investors
Pro forma net tangible book value per share after the offering
Dilution per ordinary share to new investors
Percentage of dilution in net tangible book value per ordinary share for new investors		%		%


	Shares purchased			Total consideration				Average price per share
	Number	Percent		Amount		Percent		Average price per share

Existing shareholders			%	$	€		%	$	€
New investors

Total			100%				100%


	Period-end		Average for period		Low		High
	(€ per U.S. dollar)


Year Ended December 31:
2008		0.719		0.680		0.625		0.803
2009		0.694		0.717		0.661		0.796
2010		0.748		0.754		0.687		0.837
2011		0.773		0.718		0.672		0.776
2012		0.758		0.778		0.743		0.827

Month Ended:
October 31, 2012		0.770		0.771		0.762		0.777
November 30, 2012		0.770		0.780		0.770		0.788
December 31, 2012		0.758		0.762		0.752		0.775
January 31, 2013		0.738		0.753		0.738		0.769
February 28, 2013		0.762		0.749		0.733		0.765
March 31, 2013		0.781		0.771		0.764		0.783
April 30, 2013		0.765		0.768		0.762		0.780
May 2013 (Through May 15, 2013)		0.777		0.767		0.758		0.777


	Page

Prospectus summary		1

The offering		5

Summary financial information		7

Risk factors		9

Cautionary statement regarding forward-looking statements		45

Presentation of financial and other information		46

Use of proceeds		47

Dividend policy		48

Capitalization		49

Dilution		50

Selected financial information		52

Exchange rate information		54

Management’s discussion and analysis of financial condition and results of operations		55

Business		81

Management		122

Principal shareholders		134

Related party transactions		136

Description of share capital and Articles of Association		139

Shares eligible for future sale		156

Taxation		158

Underwriting		167

Expenses of the offering		172

Legal matters		173

Experts		173

Enforcement of civil liabilities		174

Where you can find more information		175

Index to consolidated financial statements		F-1


	March 31, 2013
(€ in thousands)	Actual			Pro forma

Cash and cash equivalents	€	36,115		€

Short-term debt		280
Long-term debt, excluding current portion		6,402

Total debt		6,682


Shareholders’ equity
Share capital		290
Ordinary shares		35
Class O shares		7
Class A shares		74
Class B1 shares		83
Class B2 shares		50
Class B3 shares		41
Share premium		56,118
Other reserves		1,114
Accumulated deficit		(41,890	)
Unappropriated earnings		(3,449	)

Total shareholders’ equity(1)		12,183

Total capitalization(1)(2)		18,865


	Year ended December 31,						Three months ended March 31,
(€ in thousands)	2011			2012			2012			2013

License revenue	€	6,510		€	5,726		€	1,385		€	1,407
Collaboration revenue		2,179			2,127			589			993

Total revenue		8,689			7,853			1,974			2,400

Other income		36			174			0			1
Research and development expense		(15,348	)		(14,393	)		(3,781	)		(4,060	)
General and administrative expense		(5,203	)		(4,023	)		(1,061	)		(1,795	)
Other gains/(losses)—net		22			49			3			1

Operating loss		(11,804	)		(10,340	)		(2,865	)		(3,453	)

Finance income		434			796			212			192
Finance costs		(209	)		(348	)		(82	)		(188	)

Finance income—net		225			448			130			4

Other comprehensive income		0			0			0			0

Total comprehensive loss	€	(11,579	)	€	(9,892	)	€	(2,735	)	€	(3,449	)


Net loss per share
Basic and diluted(1)		(0.60	)		(0.37	)		(0.12	)		(0.12	)

Weighted-average shares outstanding(2)
Basic		19,240,137			26,574,570			23,145,096			29,002,298
Diluted		20,656,759			28,110,543			24,562,830			31,210,005


	As of December 31,						As of March 31,
(€ in thousands)	2011			2012			2013

Cash and cash equivalents		18,743			40,738			36,115
Working capital (deficit)(1)		(4,271	)		(2,353	)		(2,349	)
Total assets		25,191			47,329			43,360
Long-term debt, including current portion		3,032			6,541			6,682
Accumulated (deficit)		(31,122	)		(40,834	)		(44,225	)
Total shareholders’ equity		2,630			15,574			12,183


	Three months ended March 31,
	2012			2013			Change
	(€ in thousands)						%

License revenue	€	1,385		€	1,407			1.6
Collaboration revenue		589			993			68.5

Total revenue		1,974			2,400			21.6

Other income		—			1			0.0
Research and development expense		(3,781	)		(4,060	)		7.4
General and administrative expense		(1,061	)		(1,795	)		69.1
Other gains/(losses)—net		3			1			66.7

Operating loss		(2,865	)		(3,453	)		20.5

Finance income		212			192			(9.4	)
Finance costs		(82	)		(188	)		129.2

Finance income—net		130			4			(96.9	)

Net loss		(2,735	)		(3,449	)		26.1


Project expenses by project	2012		2013		Change
	(€ in thousands)				%

DMD Projects PRO044		484		364		(24.8	)
PRO045 and PRO053		910		970		6.6
Other DMD projects		928		1,186		27.8
Non-DMD projects		338		286		15.4
Infrastructure costs		1,121		1,254		11.9
Total		3,781		4,060		7.4


	Year ended December 31,
	2011			2012
	(€ in thousands)

Net cash (used in)/generated from operating activities		(7,291	)		(3,655	)
Net cash (used in)/generated from investing activities		(2,211	)		(379	)
Net cash (used in)/generated from financing activities		458			26,029

Net increase (decrease) in cash and cash equivalents		(9,044	)		21,995

Cash, cash equivalents and bank overdrafts at the beginning of the period/year	€	27,787		€	18,743

Cash, cash equivalents and bank overdrafts at the end of the period/year	€	18,743		€	40,738


	Equity capital and preferred shares		Bank loans			Other debt		Total

			(€ in thousands)

2012		22,656		(100	)		3,473		26,029
2011		5		(100	)		553		458

Total		22,661		(200	)		4,026		26,487


	Year ended December 31,				Three months ended March 31,
	2011		2012		2012		2013
	(€ in thousands)
Investments in tangible fixed assets		2,006		234		81		234
Investments in intangible assets		158		198		70		28

Total		2,164		432		151		262


	Payments due by period
	Less than 1 year		Between 1 and 2 years		Between 2 and 5 years		More than 5 years		Total
	(€ in thousands)
Debt obligations(1)(2)		100		100		300		5,769		6,269
Operating lease obligations(3)		773		773		1,327		0		2,873
Finance lease obligations(4)		243		29		0		0		272

Total		1,116		902		1,627		5,769		9,414


J.P. Morgan		Citigroup


Wedbush PacGrow Life Sciences		KBC Securities


	2011		2012


Weighted average fair value of options granted (in €)
Options with only service-based vesting conditions		0.99		0.69
Options with change of control and service-based vesting conditions		—		0.01
Options with IPO and service-based vesting conditions, €0.70 exercise price		—		1.52
Options with IPO and service-based vesting conditions, €0.01 exercise price		—		1.59
Exercise price (in €)		0.01 - 1.00		0.01 - 0.70
Risk-free interest rate		1.90%		1.50%
Volatility		60.0%		60.0%
Dividend yield		0.0%		0.0%
Expected life (in years)		2-3		1-2


Exercise price in € per share	Options

0.01		1,686,841
0.70		166,666
1.00		140,000
1.85		83,250
2.54		130,950

		2,207,707


Grant date	Options granted		Exercise price(€)		Fair value of ordinary share(€)		Per share estimated fair value of options(€)

March 22, 2011		707,500		0.01 - 1.00		1.00		0.99
September—November, 2011		8,500		0.01		1.00		0.99
January 1, 2012		10,000		0.01		0.70		0.69
March 31, 2012		15,000		0.01		0.70		0.69
July 17, 2012		61,600		0.01		0.70		0.69
October 22, 2012		31,250		0.01		0.70		0.69
December 5, 2012		1,000,000		0.01 - 0.70		0.70		0.01 - 1.59


Grant date	Restricted shares awarded		Purchase price (€)		Per share estimated fair value of restricted share (€)

March 22, 2011		78,500		0.01		1.00
October 17, 2011		11,250		0.01		1.00
December 5, 2012		115,000		0.01		0.70


Clinical trials of drisapersen
Study	Phase; study design	Total patients enrolled	Status	Dates (1)


PRO051-02	Phase I/II; open label, repeat dose escalation (extension phase ongoing 6 mg/kg/wk intermittent)	12	Complete; extension study ongoing	March 2008 – ongoing

DMD114118	Phase I; placebo- controlled, pharmacokinetics /safety	20	Complete	July 2010 – August 2012

DMD114117	Phase II; placebo-controlled, dose regimen comparison	53	Complete	September 2010 – April 2013

DMD114876	Phase II; placebo-controlled, dose-comparison	51	Ongoing	November 2011 – First quarter 2014 (expected)

DMD114044	Phase III; placebo-controlled, pivotal	186	Ongoing	December 2010 – Fourth quarter 2013 (expected)

DMD114349	Extension study for DMD114117 and DMD114044	Up to 239 (patients previously in DMD114117 and DMD114044)	Ongoing	October 2011 – ongoing


Name	Age	Position

Daan Ellens	64	Chairman
Stephen Bunting	60	Supervisory Director
Rémi Droller	37	Supervisory Director
Peter Goodfellow	61	Supervisory Director
Martijn Kleijwegt	58	Supervisory Director
David Mott	47	Supervisory Director
Jim Van heusden	42	Supervisory Director


	Shares beneficially owned before the offering				Shares beneficially owned after the offering
Name and address of beneficial owner	Number		Percent		Number		Percent

5% Shareholders
ABV IV Holdings N.V.		6,213,924		21.43		6,213,924
LSP Prosensa Pooling B.V.		6,213,924		21.43		6,213,924
New Enterprise Associates 13, L.P.(1)		6,018,633		20.75		6,018,633
Gimv N.V.(2)		2,620,248		9.03		2,620,248
Idinvest Partners(3)		2,620,248		9.03		2,620,248
MedSciences Prosensa Holding B.V.		1,996,253		6.88		1,996,253

Named Executive Officers and Directors
Hans Schikan(4)		509,970		*		509,970
Berndt Modig(5)		102,500		*		102,500
Giles Campion(6)		123,957		*		123,957
Luc Dochez(7)		127,068		*		127,068
Stephen Bunting(8)		6,213,924		21.43		6,213,924


Name and address of beneficial owner	Class B2 shares		Class B3 shares

5% Shareholders
New Enterprise Associates 13, L.P.(1)		3,304,348		2,714,285
ABV IV Holdings N.V.		478,262		392,857
LSP Prosensa Pooling B.V.		478,262		392,857
Gimv N.V.(2).		315,218		258,928
Idinvest Partners(3)		315,218		258,928
MedSciences Prosensa Holding B.V.		108,696		89,285


Number of Shares		Date

		On the date of this prospectus.
		After 180 days from the date of this prospectus (subject, in some cases, to volume limitations).
		At various times after 180 days from the date of this prospectus (subject, in some cases, to volume limitations).


Name		Number of Shares


J.P. Morgan Securities LLC

Citigroup Global Markets Inc.

Leerink Swann LLC

Wedbush Securities Inc.

KBC Securities USA, Inc

Total


	Without over-allotment exercise	With full over-allotment exercise

Per Share	$	$
Total	$	$


Expenses	Amount

U.S. Securities and Exchange Commission registration fee	$	*
FINRA filing fee		*
Nasdaq listing fee		*
Printing and engraving expenses		*
Legal fees and expenses		*
Accounting fees and expenses		*
Miscellaneous costs		*

Total		*


Condensed consolidated statement of comprehensive income (Unaudited)			F-2

Condensed consolidated balance sheet (Unaudited)			F-3

Condensed consolidated statement of changes in equity (Unaudited)			F-4

Condensed consolidated statement of cash flows (Unaudited)			F-5

Notes to the condensed consolidated financial statements (Unaudited)			F-6

Report of independent, registered public accounting firm			F-15

Consolidated statement of comprehensive income			F-16

Consolidated balance sheet			F-17

Consolidated statement of changes in equity			F-18

Consolidated statement of cash flows			F-19

Notes to the consolidated financial statements			F-20


			Three months ended March 31,
€ (‘000)	Note		2012			2013

License revenue		16		1,385			1,407
Collaboration revenue				589			993

Total revenue				1,974			2,400

Other income				—			1
Research and development expense				(3,781	)		(4,060	)
General and administrative expense				(1,061	)		(1,795	)
Other gains—net				3			1

Operating (loss)				(2,865	)		(3,453	)

Finance income				212			192
Finance costs				(82	)		(188	)

Finance income—net				130			4

Net loss				(2,735	)		(3,449	)

Other comprehensive income				—			—

Total comprehensive (loss)*				(2,735	)		(3,449	)


Loss per share from operations attributable to the equity holders of the company during the year (in € per share)

Basic and diluted loss per share				(0.12	)		(0.12	)


			As of December 31,			As of March 31,
€ (‘000)	Note		2012			2013

Assets

Non-current assets
Leasehold improvements and equipment		7		2,421			2,408
Intangible assets		8		869			839
Other financial assets		9		589			589

Total non-current assets				3,879			3,836


Current assets
Trade and other receivables		10		2,422			3,089
Prepayments		11		290			320
Cash and cash equivalents		12		40,738			36,115

Total current assets				43,450			39,524

Total assets				47,329			43,360


Equity and liabilities

Equity attributable to owners of the parent
Share capital				290			290
Share premium				56,118			56,118
Other reserves				1,056			1,114
Accumulated deficit				(31,998	)		(41,890	)
Unappropriated earnings				(9,892	)		(3,449	)

Total equity		13		15,574			12,183


Liabilities

Non-current liabilities
Borrowings—non-current portion		15		6,198			6,402
Derivative financial instruments				38			35
Deferred revenue				13,329			11,497

Total non-current liabilities				19,565			17,934


Current liabilities
Borrowings—current portion		15		343			280
Derivative financial instruments				10			8
Trade and other payables		14		5,065			5,758
Deferred revenue				6,772			7,197

Total current liabilities				12,190			13,243

Total liabilities				31,755			31,177

Total equity and liabilities				47,329			43,360


€ (‘000)	Ordinary share capital		Class O share capital		Class A share capital		Class B share capital		Total share capital		Share premium		Other reserves		Accumulated deficit			Unappropriated earnings			Total equity

Balance at January 1, 2012		31		7		74		84		195		33,557		876		(20,419	)		(11,579	)		2,630

Net loss																			(2,735	)		(2,735	)
Appropriation of result																(11,579	)		11,579
Share-based payments														90								90
Proceeds from shares issued								50		50		11,355										11,405

Balance at March 31, 2012		31		7		74		134		245		44,912		966		(31,998	)		(2,735	)		11,390

Balance at January 1, 2013		35		7		74		174		290		56,118		1,056		(31,998	)		(9,892	)		15,574

Net loss																			(3,449	)		(3,449	)
Appropriation of result																(9,892	)		9,892
Share-based payments														58								58
Proceeds from shares issued

Balance at March 31, 2013		35		7		74		174		290		56,118		1,114		(41,890	)		(3,449	)		12,183


€ (‘000)	Leasehold improvements			Laboratory equipment			Office equipment			Total


Period ended March 31, 2013

Opening net book amount		284			1,884			253			2,421
Additions					138			96			234
Depreciation charge		(9	)		(196	)		(42	)		(247	)

Closing net book amount		275			1,826			307			2,408


At March 31, 2013

Cost or valuation		340			4,253			694			5,287
Accumulated depreciation		(65	)		(2,427	)		(387	)		(2,879	)

Net book amount		275			1,826			307			2,408


€ (‘000)	Patents and licenses			Software			Total

Period ended March 31, 2013

Opening net book amount		616			253			869
Additions					28			28
Amortization charge		(23	)		(35	)		(58	)

Closing net book amount		593			246			839


At March 31, 2013

Cost		939			650			1,589
Accumulated amortization and impairment		(346	)		(404	)		(750	)

Net book amount		593			246			839


€ (‘000)	December 31, 2012		March 31, 2013

Deposit for rental obligations		89		89
Restricted cash		500		500

Total		589		589


	December 31,		March 31,
€ (‘000)	2012		2013

Trade accounts receivable		—		1
Amounts to be invoiced to partners		1,488		2,460

Trade receivables		1,488		2,461

Value-added tax		456		387
Government and other grants to be received		4		0
Interest receivables on bank accounts		473		212
Other receivables		1		29

Total		2,422		3,089