FDA approves Ultragenyx's Fayuvi, first gene therapy for Sanfilippo syndrome type A

The FDA has granted standard full approval to Ultragenyx's Fayuvi, making it the first-ever approved treatment for Sanfilippo syndrome Type A, a fatal neurodegenerative disease affecting 3,000 to 5,000 children globally. The approval is supported by trial data showing a 23.5-point cognitive score improvement over untreated patients. This milestone follows a 2025 rejection over manufacturing issues, which Ultragenyx resolved. Commercial shipments are expected to begin within 30 to 60 days.

Fayuvi FDA approval

• ▪Ultragenyx Pharmaceutical Inc. received a Priority Review Voucher from the FDA upon the approval of Fayuvi on September 17, 2026.
• ▪Fayuvi is the first-ever FDA-approved treatment designed to address the underlying cause of Sanfilippo syndrome Type A.
• ▪The U.S. Food and Drug Administration granted standard full approval to Ultragenyx Pharmaceutical Inc.'s Fayuvi (rebisufligene etisparvovec-hopf) on September 17, 2026.

Sanfilippo syndrome type A

• ▪Sanfilippo syndrome Type A is an ultra-rare, fatal lysosomal storage disease caused by a deficiency of the sulfamidase enzyme, leading to heparan sulfate accumulation and progressive neurodegeneration.
• ▪Sanfilippo syndrome Type A is estimated to affect approximately 3,000 to 5,000 patients in commercially accessible geographies, with a median life expectancy of 15 years.

Clinical trial efficacy data

• ▪Eight children treated with Fayuvi reached a 36-month cognitive development age, whereas no patients in the untreated natural history cohort achieved this milestone.
• ▪In the Transpher A trial, 17 pediatric patients treated with Fayuvi demonstrated a 23.5 point higher cognitive score over an external natural history cohort of 27 untreated patients.

Manufacturing issues resolved

• ▪The FDA previously declined to approve Fayuvi in 2025 due to manufacturing-related issues at Ultragenyx's own production facility and a third-party manufacturer.
• ▪Fayuvi is manufactured in the United States at Ultragenyx's Gene Therapy Manufacturing Facility in Bedford, Massachusetts, and Andelyn Biosciences in Columbus, Ohio.

Patient advocacy community response

• ▪Cara O'Neill, chief science officer of the Cure Sanfilippo Foundation, stated that the approval of Fayuvi provides families with a treatment action plan rather than just a terminal diagnosis.
• ▪National MPS Society and other rare disease advocates staged a demonstration at the FDA's White Oak campus in March 2026 to demand action on rare disease drug approvals.

Commercial availability timeline

• ▪Ultragenyx expects commercial shipments of Fayuvi to reach Qualified Treatment Centers within 30 to 60 days of the September 17, 2026 approval.
• ▪Ultragenyx will support patient access and insurance navigation for Fayuvi through its UltraCare program, which includes dedicated Gene Therapy Guides.