(15) REVENUE AND CREDIT CONCENTRATION

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 were to experience difficulties. The table below summarizes net product revenue concentrations based on patient location for Naglazyme, Kuvan and Firdapse and the location of Genzyme's headquarters for Aldurazyme.

		0000000000			0000000000			0000000000			0000000000
	Three Months Ended September 30,						Nine Months Ended September 30,
	2011			2010			2011			2010
Region:
United States		53	%		52	%		49	%		52	%
Europe		21	%		25	%		23	%		25	%
Latin America		16	%		13	%		15	%		12	%
Rest of World		10	%		10	%		13	%		11	%

Total net product revenue		100	%		100	%		100	%		100	%

The following table illustrates the percentage of the Company's consolidated net product revenue attributed to the Company's three largest customers.

		0000000000		0000000000		0000000000

		0000000000			0000000000			0000000000			0000000000
	Three Months Ended September 30,						Nine Months Ended September 30,
	2011			2010			2011			2010
Customer A		16	%		17	%		17	%		18	%
Customer B		21	%		17	%		18	%		18	%
Customer C		13	%		13	%		12	%		11	%

Total		50	%		47	%		47	%		47	%

The accounts receivable balances at September 30, 2011 and December 31, 2010 were comprised of amounts due from customers for net product sales of Naglazyme, Kuvan and Firdapse and Aldurazyme product transfer and royalty revenues. On a consolidated basis, the three largest customers accounted for 43%, 13% and 12% of the September 30, 2011 accounts receivable balance, compared to December 31, 2010 when the two largest customers accounted for 47% and 17% of the accounts receivable balance. As of September 30, 2011 and December 31, 2010, accounts receivable for our largest customer balance included $28.4 million and $23.1 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 performs periodic credit evaluations of its customers' financial condition and requires immediate payment in certain circumstances.