CONDENSED BALANCE SHEETS (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Current assets:
Cash and cash equivalents	$ 15,426	$ 14,002
Accounts receivable, net of allowance of $364 and $222 as of September 30, 2013 and December 31, 2012	714	569
Supplies inventory	1,392	1,050
Prepaid expenses and other current assets	2,938	710
Restricted cash		50
Total current assets	20,470	16,381
Property and equipment, net	2,826	2,446
Restricted cash	118	118
Other assets	157	122
Total assets	23,571	19,067
Current liabilities:
Accounts payable	5,604	1,888
Accrued liabilities	4,416	4,020
Deferred Genzyme co-promotion fee	2,500	2,500
Preferred stock liability		583
Total current liabilities	12,520	8,991
Long-term debt, net of discount	4,863
Deferred rent, net of current portion	250	61
Preferred stock warrant liability	252
Deferred Genzyme co-promotion fee, net of current portion	3,239	5,114
Total liabilities	21,124	14,166
Commitments and contingencies
Convertible preferred stock; $0.001 par value, 60,187,700 and 59,147,999 shares authorized at September 30, 2013 (unaudited) and December 31, 2012, respectively; 59,989,268 and 53,084,507 shares issued and outstanding at September 30, 2013 (unaudited) and December 31, 2012, respectively	79,022	63,372
Stockholders' (deficit) equity:
Common stock, $0.001 par value; 77,000,000 shares authorized; 992,578 and 667,684 shares issued and outstanding at September 30, 2013 (unaudited) and December 31, 2012, respectively	1	1
Additional paid-in capital	3,181	1,597
Accumulated deficit	(79,757)	(60,069)
Total stockholders' (deficit) equity	(76,575)	(58,471)
Total liabilities, convertible preferred stock, and stockholders' (deficit) equity	$ 23,571	$ 19,067