Ultragenyx wins FDA approval for Fayuvi gene therapy for Sanfilippo syndrome
Patients have an average lifespan of about 15 years, while an estimated 3,000 to 5,000 people in commercially accessible markets live with the condition.
USA—The US Food and Drug Administration (FDA) has approved Ultragenyx Pharmaceutical’s Fayuvi (rebisufligene etisparvovec hopf), the first disease-modifying treatment for children with Sanfilippo syndrome type A, also known as mucopolysaccharidosis type IIIA (MPS IIIA).
The rare inherited disorder progressively damages the brain and nervous system, causing children to lose cognitive, language, and other developmental abilities.
Patients have an average lifespan of about 15 years, while an estimated 3,000 to 5,000 people in commercially accessible markets live with the condition.
Gene therapy targets underlying cause
Fayuvi is administered once through an intravenous infusion and uses an adeno-associated virus serotype 9 (AAV9) vector to deliver a functional copy of the SGSH gene into patients’ cells.
The treatment enables cells to produce sulfamidase, an enzyme that patients with MPS IIIA lack or produce at insufficient levels.
Sulfamidase breaks down heparan sulfate in lysosomes, helping reduce the accumulation of the complex sugar molecule that contributes to disease progression and neurological damage.
The FDA based its decision on data from a single-arm clinical trial, including measurements of heparan sulfate in cerebrospinal fluid and neurodevelopmental outcomes. Researchers compared the results with data from the disease’s natural history.
Among 17 children younger than two years or at an earlier stage of the disease, a single Fayuvi infusion produced a 23.2-point treatment effect on cognitive scores measured with the Bayley Scales of Infant and Toddler Development, Third Edition, compared with natural history data.
Eight children reached a developmental age of 36 months, while none in the natural history cohort reached that milestone.
Among 10 older children or those treated at a later disease stage, at least one functional ability was maintained in three assessed areas at their latest evaluation.
Treatment costs US$3.95 M
Ultragenyx said Fayuvi will have a US wholesale acquisition cost of US$3.95 million, the list price before discounts, rebates, or potential outcome-based reimbursement arrangements.
The company said the lifetime cost of caring for a child with Sanfilippo syndrome type A can exceed US$8 million. Fayuvi will be available through qualified treatment centres trained to administer gene therapies.
“Fayuvi marks a historic moment for children and families living with MPS IIIA,” said Kyle Diamantas, acting FDA commissioner.
He added that gene therapy could address rare diseases for which patients have limited treatment options.
Ultragenyx CEO Emil Kakkis said the company would work with treatment centres and payers to support timely access to the therapy.
FDA approval follows regulatory setback
The approval follows an earlier regulatory setback.
In 2025, the FDA declined to approve Fayuvi because of manufacturing issues involving Ultragenyx’s gene therapy facility and a third-party manufacturer.
The FDA accepted the company’s resubmission in April 2026 and granted it priority review.
Ultragenyx now manufactures Fayuvi at its facility in Bedford, Massachusetts, and through Andelyn Biosciences in Columbus, Ohio.
The approval also qualifies Ultragenyx for a priority review voucher under the FDA’s rare paediatric disease programme.
The company can use the voucher to accelerate the review of another product or sell it.
Fayuvi is Ultragenyx’s second approved gene therapy, following Genglycos (pariglasgene brecaparvovec), which the FDA approved for glycogen storage disease type Ia in August 2026.
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