Ultragenyx Shares Rise After FDA Approval for Sanfilippo Syndrome Treatment

03:57 PM EDT, 09/17/2026 (MT Newswires) -- Ultragenyx Pharmaceutical (RARE) shares rose 11% after the company won FDA approval for Fayuvi, the first treatment for children with Sanfilippo syndrome type A, a rare genetic condition that progressively damages the brain and nervous system. Delivered as a one-time IV infusion, Fayuvi uses a modified virus to deliver a healthy gene, replacing the enzyme the patients lack. the FDA said Thursday in a statement. In clinical trials, treated children aged 2 to 5 maintained or improved their cognitive abilities compared to historical patient outcomes, the agency said. The FDA noted common side effects like fever, nausea, and elevated liver enzymes. The label also warns of potential long-term risks, including blood clotting issues and tumor formation, requiring patients to take immune-suppressing steroids around the time of treatment. Price: 14.34, Change: +1.46, Percent Change: +11.34