Ultragenyx gets FDA approval for first Sanfilippo gene therapy

The U.S. FDA has granted full approval to Ultragenyx Pharmaceutical’s AAV9 gene therapy UX111, branded Fayuvi, for the treatment of pediatric patients with mucopolysaccharidosis type IIIA (MPS IIIA, Sanfilippo syndrome Type A).

The approval marks the first-ever FDA-approved treatment for Sanfilippo syndrome Type A, a rare fatal lysosomal storage disease that primarily affects the brain. Along with the approval, Ultragenyx received a priority review voucher.

Ultragenyx expects Fayuvi will be available at specialized treatment centers within 30 to 60 days. The U.S. list price has been set at $3.95 million.

The FDA accepted Ultragenyx’s initial BLA for UX111 back in February 2025, granting it priority review and assigning a PDUFA action date of August 18, 2025. Then, in July 2025, the agency issued a CRL, citing specific CMC-related observations from recently completed manufacturing facility inspections. Ultragenyx said the issues were resolvable as they were “related to facilities and processes and are not directly related to the quality of the product.” The company resubmitted its BLA in February 2026.

Fayuvi is designed to address the underlying SGSH enzyme deficiency responsible for abnormal accumulation of heparan sulfate, a glycosaminoglycan, in the brain that results in progressive cell damage and neurodegeneration. It is dosed in a one-time intravenous infusion using a self-complementary AAV9 vector to deliver a functional copy of the SGSH gene to cells.

Fayuvi’s green light is the second gene therapy approval for Ultragenyx. Last month, the FDA granted accelerated approval to Genglycos for use in adult and pediatric patients eight years and older with glycogen storage disease type Ia.