Ultragenyx stock surges 10% on FDA approval for gene therapy

Ultragenyx Pharmaceutical's shares surged 10% on Friday following the FDA's approval of Fayuvi, marking the first gene therapy for mucopolysaccharidosis type IIIA, or Sanfilippo syndrome type A. This is the first FDA-authorized treatment for pediatric patients with MPS IIIA, a rare inherited disease that damages the brain and nervous system over time.

Before this approval, there were no treatments to alter the disease's progression. Fayuvi is an intravenous gene therapy administered once, using a modified adeno-associated virus serotype 9 to introduce a functional copy of the SGSH gene into a patient's cells, enabling them to produce the missing sulfamidase enzyme. The therapy's safety and efficacy were demonstrated in a study of pediatric patients aged 2 to 5 years, showing maintained or improved cognitive function compared to untreated patients.

The FDA highlighted potential risks such as increased liver enzymes, nausea, fever, decreased white blood cell and platelet counts, and elevated amylase, as well as a risk of thrombotic microangiopathy and long-term tumor development. Patients must receive corticosteroid treatment before each infusion, which must be administered in a healthcare setting equipped to handle infusion reactions. The FDA granted Fayuvi Orphan Drug, Fast Track, and Breakthrough Therapy designations.