The FDA has approved Ultragenyx’s gene therapy rebisufligene etisparvovec (Fayuvi, formerly UX-111), marking the first approved disease-modifying treatment for Sanfilippo syndrome type A (MPS IIIA). The single-dose AAV-based therapy is designed to restore functional SGSH enzyme activity in patients with progressive neurodegeneration and premature death. The agency’s decision comes after a prior complete response letter in 2025, when the FDA cited manufacturing-process concerns. With today’s approval, Ultragenyx positioned Fayuvi as indicated across the full pediatric age range for MPS IIIA. Ultragenyx framed the approval as a landmark for families who previously had no approved therapy to alter the course of the disease. Patient advocates and FDA leadership emphasized the intent to provide earlier access to a treatment aimed at the underlying cause rather than only symptomatic care.