FDA Grants Standard Full Approval of Ultragenyx FAYUVI (Rebisufligene Etisparvovec-Hopf) as First-Ever Treatment for Pediatric Sanfilippo Syndrome Type A / MPS IIIA; $3.95M WAC Price and Priority Review Voucher Awarded
Ultragenyx Pharmaceutical Inc. (NASDAQ: RARE) announced Thursday September 17, 2026 that the FDA granted standard full approval to FAYUVI (rebisufligene etisparvovec-hopf, previously UX111) — a one-time intravenous AAV9-delivered gene therapy carrying a functional copy of the SGSH (N-sulfoglucosamine sulfohydrolase) gene — for the treatment of pediatric patients with mucopolysaccharidosis type IIIA (MPS IIIA, Sanfilippo syndrome Type A). MPS IIIA is a progressive, ultimately fatal autosomal-recessive lysosomal storage disorder that causes rapid neurodegeneration in early childhood; before Thursday, no disease-modifying therapy existed. The approval landed two days ahead of the September 19 PDUFA action date, followed the July 2025 complete response letter that had cited chemistry-manufacturing-controls issues plus manufacturing-site observations. The clinical package supporting standard full approval (not accelerated): up to 8 years of follow-up in treated children, sustained cerebrospinal fluid heparan sulfate reduction (the accumulating substrate), and a 23.5-point cognitive-score advantage over natural-history controls. Ultragenyx received a Rare Pediatric Disease Priority Review Voucher — historically valued $150-350 million on the secondary market — alongside the approval, plus U.S. per-patient wholesale acquisition cost set at $3.95 million. RARE shares closed the day up 13% and extended gains after hours. FAYUVI is manufactured domestically at Andelyn Biosciences in Columbus, Ohio and Ultragenyx's own Bedford, Massachusetts facility. Second gene therapy approval for the company.