(19) REVENUE AND CREDIT CONCENTRATIONS

Net Product Revenue - The Company considers there to be revenue concentration risks for regions where net product revenue exceeds 10% of consolidated net product revenue. The concentration of the Company’s net product revenue within the regions below may have a material adverse effect on the Company’s revenue and results of operations if sales in the respective regions experience difficulties.

The table below summarizes consolidated net product revenue concentrations based on patient location for Vimizim, Naglazyme, Kuvan and Firdapse which are sold directly by the Company and global sales of Aldurazyme which is marketed by Genzyme. Genzyme is the Company’s sole customer for Aldurazyme and is responsible for marketing and selling Aldurazyme to third-parties.

	Years Ended December 31,
	2016			2015			2014
Region:
United States		37	%		39	%		37	%
Europe		23	%		19	%		18	%
Latin America		13	%		16	%		16	%
Rest of world		19	%		15	%		15	%
Total net product revenues marketed by the Company		92	%		89	%		86	%
Aldurazyme net product revenues marketed by Genzyme		8	%		11	%		14	%
Total net product revenue		100	%		100	%		100	%

The following table illustrates the percentage of the Company’s consolidated net product revenues attributed to the Company’s largest customers.

	For the Years Ended December 31,
	2016			2015			2014
Customer A		19	%		15	%		15	%
Customer B		13	%		13	%		11	%
Customer C		10	%		—			—
Customer D		8	%		11	%		14	%
Customer E		6	%		10	%		12	%
Total		56	%		49	%		52	%

On a consolidated basis, the Company’s two largest customers accounted for 26% and 20% of the December 31, 2016 accounts receivable balance, respectively, compared to December 31, 2015 when the two largest customers accounted for 37% and 18% of the accounts receivable balance, respectively. As of December 31, 2016 and 2015, accounts receivable balance for Genzyme included $30.7 million and $36.1 million, respectively, of unbilled accounts receivable related to net incremental Aldurazyme product transfers to Genzyme. The Company does not require collateral from its customers, but does perform periodic credit evaluations of its customers’ financial condition and requires immediate payment in certain circumstances.

The Company is subject to credit risk from accounts receivable related to product sales. The majority of the Company’s trade accounts receivable arises from product sales in the U.S. and the European Union (the EU). The Company’s product sales to government-owned or government-funded customers in certain European countries, including Greece, Italy, Portugal, Spain and Russia, are subject to payment terms that are statutorily determined. Because these customers are government-owned or government-funded, the Company may be impacted by declines in sovereign credit ratings or sovereign defaults in these countries. A significant or further decline in sovereign credit ratings or a default in these countries may decrease the likelihood that the Company will collect accounts receivable or may increase the discount rates and the length of time until receivables are collected, which could result in a negative impact to the Company’s operating results. In the year ended December 31, 2016, the Company’s net product revenues for these countries was 6%. Additionally, approximately 11% of the Company’s outstanding accounts receivable at December 31, 2016 related to such countries.

As of December 31, 2016, the Company’s accounts receivable in certain European countries, specifically Greece, Italy, Portugal, Spain and Russia, totaled approximately $23.5 million, of which $1.6 million were greater than 90 days past due.

The Company also sells its products in other countries that face economic crises and local currency devaluation. Although the Company has historically collected receivables from customers in those countries, sustained weakness or further deterioration of the local economies and currencies may cause customers in those countries to be unable to pay for the Company’s products. The Company has not historically experienced a significant level of uncollected receivables and has received continued payments from its more aged accounts. The Company believes that the allowances for doubtful accounts related to these countries is adequate based on its analysis of the specific business circumstances and expectations of collection for each of the underlying accounts in these countries.