FDA Approves Fayuvi — First Disease-Modifying Gene Therapy For Sanfilippo Syndrome Type A

The US Food and Drug Administration (FDA) has approved Fayuvi (rebisufligene etisparvovec-hopf), Ultragenyx Pharmaceutical's one-time gene therapy for Sanfilippo syndrome type A (mucopolysaccharidosis IIIA, MPS IIIA). This marks the first approved disease-modifying treatment (DMT) for children with this rare, progressive neurodegenerative disorder.

What Fayuvi Does

Fayuvi is administered as a single intravenous infusion using an adeno-associated virus serotype 9 (AAV9) vector to deliver a functional copy of the SGSH gene into patients' cells. Restoring SGSH allows production of the enzyme sulfamidase, which helps break down heparan sulfate in lysosomes and reduces its damaging accumulation in the brain and other tissues.

Clinical Evidence

Clinical trial data showed that a single IV dose of Fayuvi maintained or improved cognitive function compared with an untreated historical control cohort. In other words, treated children diverged from the expected natural course of disease progression, demonstrating an impact on the underlying disorder rather than only managing symptoms.

Karim Mikhail, director of the FDA's Center for Biologics Evaluation and Research (CBER), said approval is a meaningful advance for affected children and families and highlights gene therapy's potential to address rare, devastating diseases where urgent treatment is needed.

Access, Distribution, And Cost

Fayuvi will be made available through a network of qualified treatment centers (QTCs) — specialized sites trained to administer gene therapy and manage associated care. On an investor call, Ultragenyx announced a US list price of $3.95 million for the treatment. The company cited analyses that lifetime care for a child with Sanfilippo type A can exceed $8 million as context for pricing; high prices for gene therapies are also driven by small patient populations, complex manufacturing, and substantial development costs.

Emil Kakkis, Ultragenyx CEO, said the company recognizes the urgency for families and will work with treatment centers and payers to support timely access and the patient journey following gene therapy administration.

Regulatory And Commercial Notes

As part of the approval for a rare pediatric disease, Ultragenyx received a Priority Review Voucher (PRV), which can accelerate FDA review for another product or be sold; such vouchers currently trade in the roughly $150 million to $200 million range. Fayuvi is Ultragenyx’s second gene therapy approval this year, following an August approval for a gene therapy to treat glycogen storage disease type Ia (GSDIa), which carries a list price of about $2.7 million.

Sanfilippo syndrome type A is a rare inherited condition that progressively impairs cognitive, language, and other developmental abilities. Patients typically have a shortened life expectancy, with average survival estimates around 15 years. The condition is estimated to affect roughly 3,000 to 5,000 people across commercially accessible regions.

Source: Original reporting by Pharmaceutical Technology, a GlobalData-owned brand. This article summarizes the FDA approval, clinical findings, and commercial context for Fayuvi.