--- title: "FDA approves first treatment for Sanfilippo syndrome type A" canonical: https://smallgoodthings.org/stories/fda-approves-first-treatment-sanfilippo-type-a-2026/ sourceName: "U.S. Food and Drug Administration" sourceUrl: "https://www.fda.gov/news-events/press-announcements/fda-approves-first-gene-therapy-pediatric-patients-sanfilippo-syndrome-type" datePublished: 2026-10-23T00:00:00.000Z dateModified: 2026-10-23T00:00:00.000Z --- # FDA approves first treatment for Sanfilippo syndrome type A On 17 September 2026, the US Food and Drug Administration approved Fayuvi, the first treatment for children with Sanfilippo syndrome type A (MPS IIIA). Until now, care was limited to managing symptoms. The one-time gene therapy helps the body make an enzyme the disease leaves missing. ## What happened? On 17 September 2026, the US Food and Drug Administration (FDA) approved Fayuvi. It is the first treatment for children with mucopolysaccharidosis type IIIA, also known as Sanfilippo syndrome type A or MPS IIIA. The approval went to Ultragenyx Pharmaceutical. Until now, treatment was limited to managing symptoms. No approved therapy aimed to change the course of the disease. ## What is Sanfilippo syndrome type A? MPS IIIA is a rare inherited disease. The FDA says it progressively damages the brain and nervous system. Children lose cognitive, language and other abilities they had developed. pharmaphorum reports that the disease cuts average lifespan to around 15 years. ## How does the treatment work? Fayuvi is a one-time gene therapy given into a vein. It uses a modified, non-infectious virus, called adeno-associated virus serotype 9, to deliver a working gene. This lets the body's cells make sulfamidase, the enzyme that is missing or deficient in MPS IIIA. ## What was the evidence? The FDA evaluated Fayuvi in an open-label, single-arm study across several centres. Children treated with Fayuvi maintained or improved their cognitive function compared with an untreated historical control group. WebMD reports that 17 treated children were compared with 27 untreated children who were not part of the study. The most common side effects included increased liver enzymes, nausea and vomiting, fever and decreased appetite. Safety warnings include a risk of thrombotic microangiopathy, a condition involving small blood clots. "Parents and clinicians have been waiting far too long for an option," said the director of the FDA's Center for Biologics Evaluation and Research. ## What happens next? pharmaphorum reports that Fayuvi will launch with a list price of $3.9 million. Ultragenyx said it hoped to make it available through treatment centres within 30 to 60 days of approval. ## What this does not show The study was small and did not randomly assign children to treatment. How long the benefit lasts is not yet known. The FDA also notes a potential long-term risk linked to the inserted genetic material. The approval covers the United States only. Families elsewhere should ask their specialist about trials or access routes in their own country. ## Reporting notes We checked the FDA's release of 17 September 2026 and reports from WebMD and pharmaphorum. The approval rests on a small single-arm study compared with untreated children from outside the study, not a randomised trial. The FDA release gives no numerical results. Price and launch timing come from the company via pharmaphorum. The approval applies in the United States only. ## Sources - [U.S. Food and Drug Administration · 17 September 2026](https://www.fda.gov/news-events/press-announcements/fda-approves-first-gene-therapy-pediatric-patients-sanfilippo-syndrome-type): The FDA's approval announcement, including how the therapy works, the study design and safety warnings. - [WebMD · 21 September 2026](https://www.webmd.com/drugs/updates/fayuvi-sanfilippo-syndrome-type-a): Reports the comparison of 17 treated children with 27 untreated children. - [pharmaphorum · 18 September 2026](https://pharmaphorum.com/news/ultragenyx-gets-fda-nod-first-sanfilippo-gene-therapy): Reports the list price, launch timing and average lifespan with the disease. - [MedlinePlus Genetics · Mucopolysaccharidosis type III](https://medlineplus.gov/genetics/condition/mucopolysaccharidosis-type-iii/): US National Library of Medicine background on Sanfilippo syndrome. ## Common questions ### What is Sanfilippo syndrome type A? It is a rare inherited disease, also called MPS IIIA. The FDA says it progressively damages the brain and nervous system, causing children to lose cognitive, language and other developmental abilities. ### How strong is the evidence for Fayuvi? The FDA approved it on the basis of an open-label, single-arm study in children. Treated children maintained or improved cognitive function compared with an untreated historical control group. It was not a randomised trial, and long-term durability is unknown. Primary source: [U.S. Food and Drug Administration](https://www.fda.gov/news-events/press-announcements/fda-approves-first-gene-therapy-pediatric-patients-sanfilippo-syndrome-type)