FAYUVI (rebisufligene etisparvovec-hopf)

September 17, 2026: Ultragenyx Pharmaceutical (NASDAQ: RARE) said the FDA granted standard full approval to FAYUVI (rebisufligene etisparvovec-hopf; UX111), an AAV9 gene therapy, for pediatric patients with mucopolysaccharidosis type IIIA (MPS IIIA, Sanfilippo syndrome type A) with preserved neurodevelopmental function. The company said FAYUVI is the first FDA-approved treatment for Sanfilippo syndrome type A and that it received a Priority Review Voucher.

Approval was supported by the pivotal Transpher A trial and long-term follow-up studies, with clinical data extending to nearly 8 years. In the modified intent-to-treat population, treated patients (N=17) showed a 23.5-point higher Bayley-III Cognitive raw score versus an untreated external natural-history cohort (N=27) from 24 to 60 months of age (p<0.0001). The release also cited sustained reductions in CSF heparan sulfate across age groups and an acceptable safety profile.

Ultragenyx expects commercial product shipment to Qualified Treatment Centers within 30-60 days and will support access through its UltraCare program. The most common adverse reactions reported were increased liver enzymes, vomiting, abnormal behavior, diarrhea, pyrexia, decreased white blood cell count, Cushingoid features, and decreased appetite. Ultragenyx scheduled a conference call for September 17, 2026 at 5:30 p.m. ET.