Ultragenyx says the US Food and Drug Administration has approved Fayuvi, a one-time gene therapy for the neurologic effects of Sanfilippo syndrome type A in children. STAT reports that it is the first FDA-approved treatment for the disease, a fatal inherited condition that attacks the brain in childhood.
What happened
Ultragenyx announced the approval on 17 September. The full name of the product is FAYUVI (rebisufligene etisparvovec-hopf), and the approved use is precise: “treatment of neurologic manifestations of mucopolysaccharidosis type IIIA (MPS IIIA, Sanfilippo syndrome type A) in pediatric patients.”
Two details in the announcement stand out. The therapy is given as a single intravenous dose, and it received what Ultragenyx calls “standard full approval,” rather than a conditional pathway.
The evidence comes from a trial that compared 17 treated children with 27 children from natural history records, meaning children with the disease who were followed over time without this treatment. According to the company, treated patients showed a “23.5 point higher (p<0.0001) cognitive score over natural history,” with follow-up “up to nearly 8 years.”
The company also received a Priority Review Voucher with the approval. STAT reported that pricing was not disclosed.
How it works
Sanfilippo syndrome type A is a genetic disease: children are born with a fault in their DNA that, over time, damages the brain. According to Ultragenyx, median life expectancy is about 15 years.
Gene therapy aims at the root of that problem by delivering working genetic instructions to the body’s cells. The difficult part here is the destination. The brain is protected by tight defences that keep most substances in the bloodstream out, which is why getting a treatment to it from a vein is so hard.
Fayuvi uses a delivery vehicle known as AAV9. An AAV is a virus that has been emptied of its own genes and repurposed as a carrier, a bit like a sealed courier envelope that is designed to reach a particular address and deliver the letter inside. In this case the letter is the genetic instruction, and the address includes the brain. The therapy is given as one intravenous infusion, which is why this approval is being described as gene therapy reaching the brain through a single infusion.
By the numbers
| Item | Figure | Source |
|---|---|---|
| Treated patients in the trial | 17 | Ultragenyx |
| Natural history comparison patients | 27 | Ultragenyx |
| Cognitive score difference | 23.5 points higher (p<0.0001) | Ultragenyx |
| Longest follow-up | Up to nearly 8 years | Ultragenyx |
| Median life expectancy with the disease | About 15 years | Ultragenyx |
| Type of approval | Standard full approval | Ultragenyx |
| Price | Not disclosed | STAT |
Why it matters
Families of children with Sanfilippo syndrome type A have had no approved treatment until now. That alone makes this a significant day for a small community that has waited a long time.
What caught my attention is the length of the follow-up. Up to nearly 8 years is a long window for a gene therapy trial in a rare childhood disease, and it gives the cognitive results more depth than a short study could.
The approval also carries a wider scientific message. It shows a gene therapy delivered by a single infusion into a vein reaching the brain well enough to earn full approval for its neurologic effects. Other brain diseases that researchers hope to treat with gene therapy face the same delivery problem.
It is just as important to be clear about the limits. Fayuvi is not a cure. It is approved for the neurologic manifestations of the disease in children, and the company’s own wording is about cognitive scores, not about ending the illness. The comparison was with natural history records, not with a placebo group, and the trial included 17 treated patients, a small group even if typical for a rare disease. All of the trial figures here come from the company’s announcement.
What comes next
Ultragenyx has not disclosed a price, so the most practical question for families, cost and access, remains open as of today. In my view, that answer will shape how quickly the approval turns into treatment for children who need it. Decisions about any therapy belong to families and their doctors, and nothing in this article is medical advice.
Sources
- Ultragenyx, press release announcing FDA approval of Fayuvi gene therapy for Sanfilippo syndrome type A (MPS IIIA), 17 September 2026, https://www.globenewswire.com/news-release/2026/09/17/3364357/20739/en/ultragenyx-announces-approval-of-fayuvi-gene-therapy-the-first-ever-fda-approved-treatment-for-sanfilippo-syndrome-type-a-mps-iiia.html
- STAT, report on the approval of Ultragenyx’s Sanfilippo syndrome treatment, 17 September 2026, https://www.statnews.com/2026/09/17/sanfilippo-syndrome-treatment-ultragenyx-approval/
- Fierce Pharma, report on the FDA approval of Fayuvi for a rare neurodegenerative disorder, September 2026, https://www.fiercepharma.com/pharma/fda-approves-ultragenyx-gene-therapy-fayuvi-rare-neurodegenerative-disorder