Ultragenyx Pharmaceutical has won FDA approval for its gene therapy Fayuvi, marking a historic milestone for children diagnosed with a rare and fatal neurodegenerative disorder.
The U.S. Food and Drug Administration granted standard full approval for FAYUVI (rebisufligene etisparvovec-hopf), also known as UX111, on September 17, 2026, ahead of its assigned PDUFA action date.
Fayuvi is approved for pediatric patients with mucopolysaccharidosis type IIIA, commonly known as Sanfilippo syndrome Type A, a progressive and fatal lysosomal storage disease.
The approval represents the first-ever FDA-sanctioned treatment for Sanfilippo syndrome Type A, a disease that has long had no disease-modifying options available to patients.
This milestone also marks Ultragenyx’s second gene therapy approval and its sixth FDA approval overall, reinforcing the company’s position in the rare disease space.
Sanfilippo syndrome Type A primarily attacks the brain, causing rapid and progressive neurodegeneration that begins in early childhood and leads to early death.
Children diagnosed with the condition typically experience progressive global developmental delay, followed by the loss of cognitive, language, and motor function over time.
The disease is caused by a deficiency of an enzyme called sulfamidase, leading to a toxic accumulation of a complex sugar molecule known as heparan sulfate in the body and brain.
Sanfilippo syndrome Type A is estimated to affect approximately 3,000 to 5,000 patients in commercially accessible geographies, with a median life expectancy of just 15 years.
FAYUVI is a single-dose intravenous AAV9 gene therapy designed to deliver a functional copy of the deficient enzyme gene, enabling the body to express and replace the missing SGSH enzyme.
The path to approval was not without obstacles, as Ultragenyx had previously received a complete response letter in 2025 before resubmitting its biologics licence application on January 30, 2026.
The resubmission incorporated an additional year of long-term follow-up data across multiple biomarker and clinical measures, strengthening the evidence base presented to regulators.
The FDA accepted the resubmission on April 2, 2026, and assigned a new PDUFA action date of September 19, 2026, before ultimately approving Fayuvi two days ahead of schedule.
Ultragenyx received a Priority Review Voucher upon the approval, a tradeable asset that holds significant financial value within the pharmaceutical industry.
The company’s UltraCare programme will facilitate patient access to Fayuvi, with the therapy expected to be shipped to Qualified Treatment Centers within 30 to 60 days of approval.