Fayuvi gene therapy cleared for Sanfilippo syndrome type A

What this means

Sanfilippo syndrome type A (MPS IIIA) is a rare inherited disease in which the body cannot break down a specific type of large sugar molecule (heparan sulfate) because of a missing enzyme (SGSH). These molecules build up inside cells, and affected children lose developmental milestones — speech, thinking, mobility — starting in early childhood, with the disease usually fatal in the teenage years. Until this approval, no FDA-approved therapy existed that targeted the underlying disease; care was limited to managing symptoms. FAYUVI (rebisufligene etisparvovec-hopf, previously UX111) is Ultragenyx's single-dose intravenous gene therapy that uses an AAV9 viral vector to carry a working copy of the SGSH gene into cells throughout the body, allowing them to make the enzyme they lack. FDA approved it on September 17, 2026 — two days ahead of the September 19 PDUFA target — for use in pediatric patients with MPS IIIA who still have preserved neurodevelopmental function, i.e. those treated before major cognitive loss has set in. FAYUVI's pivotal Transpher A trial measured a 23.5-point higher Bayley-III Cognitive raw score change from 24 to 60 months of age versus natural history (p<0.0001). FAYUVI is the first-ever FDA-approved treatment for Sanfilippo syndrome type A, Ultragenyx's second approved gene therapy and its sixth FDA approval overall; Ultragenyx also received a Priority Review Voucher on approval. Manufacturing runs at Andelyn Biosciences (Columbus, OH) and Ultragenyx's own facility in Bedford, MA.