FDA Clears Fayuvi as First Therapy for Pediatric Sanfilippo Syndrome A

What changed

The U.S. FDA approved Ultragenyx Pharmaceutical's Fayuvi (rebisufligene etisparvovec) on 17 September 2026 for neurologic manifestations of mucopolysaccharidosis type IIIA (Sanfilippo syndrome type A) in pediatric patients with preserved neurodevelopmental function. Ultragenyx announced the commercial brand on 18 September 2026.

Fayuvi is an adeno associated virus gene therapy delivering a functional SGSH gene copy to address enzyme deficiency that drives progressive cognitive decline. The approval follows a July 2025 complete response letter tied to manufacturing questions and a March 2026 complete response submission. Pivotal Phase 1/2 data showed biomarker and cognitive improvements versus an external natural history control.

BioSpace reported Fayuvi is priced near $4 million as a one time therapy. Ultragenyx received a priority review voucher it intends to sell; William Blair analysts cited a roughly $200 million market rate for PRVs.

Why it matters

Sanfilippo type A previously had no approved disease modifying therapy. Payers, hospital pharmacy committees, and rare disease centers must now build access pathways for a ultra high cost one time gene therapy with narrow neurodevelopmental eligibility. The approval also marks Ultragenyx's second gene therapy in two months after Genglycos for glycogen storage disease type Ia.

For portfolio strategists, the Fayuvi arc shows FDA willingness to approve after manufacturing remediation, but with strict functional inclusion criteria. Gene therapy financings will cite Fayuvi pricing and PRV liquidity as comparables.

Who is affected

Pediatric neurology and metabolic disease centers managing Sanfilippo referrals. Payer medical policy teams drafting coverage for preserved function definitions and post treatment monitoring. Ultragenyx investors weighing PRV sales against launch costs for a ultra rare population. Competing gene therapy developers in lysosomal storage diseases watching real world uptake and CMS or commercial payer responses.

What to do next

Rare disease program leads should map Fayuvi label language on preserved neurodevelopmental function against your patient registry inclusion criteria. Payer teams should model one time therapy budgets with outcomes based follow up requirements before Q4 2026 policy updates.

What to watch

Ultragenyx launch metrics and confirmed net price after rebates. FDA post marketing requirements listed in the 17 September 2026 approval letter. Whether European regulators follow after prior MAA interactions. Sale timing and price of the new priority review voucher.

Sources

• Primary — FDA, September 17, 2026 Approval Letter FAYUVI (17 September 2026). Formal BLA approval, indication, and manufacturing authorization.
• Primary — BioSpace, Ultragenyx wins FDA greenlight for first Sanfilippo therapy, priced at nearly $4M (18 September 2026). Commercial context, pricing report, and PRV plans.
• Secondary — Ultragenyx, company release cited in trade coverage (18 September 2026). Brand launch and first therapy claim for Sanfilippo type A.