Shares of Ultragenyx Pharmaceutical climbed after the Food and Drug Administration said it approved the company's Fayuvi for children with Sanfilippo syndrome type A.

The stock gained 12%, to $14.44, late Thursday, but has fallen 37% for the year.

The agency said this is the first approved treatment for Sanfilippo syndrome type A, a rare inherited disease that damages the brain and nervous system.

"Until today, treatment was limited to managing symptoms; there was no FDA-approved therapy designed to change the underlying course of the disease," the FDA said.

Ultragenyx previously said there was a Sept. 19 Prescription Drug User Fee Act action date for the drug.