Fayuvi Opens a Narrow Door for Sanfilippo Type A

The FDA on September 17, 2026 approved Fayuvi, the first gene therapy for Sanfilippo syndrome type A. Ultragenyx Pharmaceutical’s one-time intravenous infusion is cleared only for children who still have preserved neurodevelopmental function. The company set a U.S. wholesale acquisition cost of $3.95 million.

That is a real drug for a disease that until last week had none. It is also a narrower offer than the headline. The label covers neurologic signs of type A in pediatric patients whose skills remain. It does not cover types B, C, or D, and it does not restore what the disease has already taken.

Fayuvi’s Label Leaves Most Sanfilippo Kids Outside

Fayuvi (rebisufligene etisparvovec-hopf) is an AAV9 vector that carries a working copy of SGSH, the gene for the sulfamidase enzyme. In type A, that enzyme is missing, so heparan sulfate piles up in cells and wrecks the brain. The shot is given into a vein over about an hour. Transduced cells then make the enzyme and share it with nearby neurons.

The FDA the first treatment for pediatric patients with mucopolysaccharidosis type IIIA, also called MPS IIIA. Acting Commissioner Kyle Diamantas said the disease had, until this approval, offered no licensed therapy that could change its course. Karim Mikhail, director of the Center for Biologics Evaluation and Research, called the usual path a relentless regression after a normal start in the earliest years.

The binding limit sits in one phrase: preserved neurodevelopmental function. Ultragenyx did not publish a hard upper age. That wording is already being read as a wider door than a cutoff at 2 or 5 would have been. It still shuts out children who have already lost language, walking, or the ability to engage, which is how type A typically moves after the toddler years.

Sanfilippo type A is estimated to affect about 3,000 to 5,000 patients in commercially reachable countries, with a median life expectancy of 15 years. A United Kingdom mortality series put the mean age at death of 15.22 years for type A, a separate figure from a different study and era. Families often hear the nickname childhood Alzheimer’s. Kids lose speech, sleep, toilet skills, then mobility, and many die in their teens.

A 23.5-Point Gap Against Natural History

Approval rests on the Transpher A gene transfer trial and long-term follow-up, with data now stretching to nearly 8 years. There was no placebo arm. Treated children were scored against an external natural history group on the Bayley-III cognitive raw score between 24 and 60 months of age, the window when untreated type A usually flattens and then falls.

TRANSPHER A AND THE OLDER COHORT

The 23.5 point gap is the number Ultragenyx cited as the basis for standard full approval, not an accelerated nod on a biomarker alone. Cerebrospinal fluid heparan sulfate fell across age groups, which the company used as biochemical proof that the missing enzyme was being replaced. Eight of the 17 children treated early reached the cognitive developmental age of a 3-year-old, a mark none of the untreated natural history children hit.

The commercial dose is 3 x 10^13 vector genomes per kilogram. Earlier low-dose cohorts, including the first child treated, got less. That matters for how to read decade-long stories from 2016: those children did not receive the regimen now on the label.

Eliza O’Neill Took the First Dose in 2016

Haiyan Fu and Doug McCarty built the vector at Ohio State University and Nationwide Children’s Hospital. Abeona Therapeutics took it into humans as ABO-102. In May 2016, Eliza O’Neill, then six and a half, became the first person dosed, at the low starting amount, at Nationwide Children’s in Columbus, Ohio.

Her parents, Glenn and Cara O’Neill, had founded the Cure Sanfilippo Foundation after Eliza’s diagnosis at age 3. A video, Saving Eliza, brought in about $2 million, money the foundation later said helped manufacture the experimental product. The family spent just shy of two years in isolation so Eliza would not pick up AAV9 antibodies that would have barred her from the trial. Kevin Flanigan, director of the Center for Gene Therapy at Nationwide Children’s, was the principal investigator. He said the vector was first developed there more than a decade ago.

This, gosh, would just finally mean when patients and families receive this shocking diagnosis, they wouldn’t be told to take their kids home and love them. They would be given hope and an action plan for treatment.

Cara O’Neill, chief science officer, Cure Sanfilippo Foundation

Cara O’Neill, a pediatrician, told a Senate aging panel on February 26, 2026 that Eliza, then 16, had lived past the average life span, had never had a seizure, and could run on the beach and play in the water. She is in a special class and still gets therapy. The infusion did not rewind the injury already done to her neurons. It is the younger, higher-dose children whose scores now sit on the label.

In May 2022 Abeona licensed global rights to Ultragenyx after funding ran short despite the data. Glenn O’Neill, president of the foundation, and Terri Klein, president and chief executive of the National MPS Society, said the community should honor every family who contributed and remember the children lost while waiting. About 28 children were treated across the original study cohorts before the commercial product existed.

After the 2025 Manufacturing Rejection

Clinical reviewers had already called the neurodevelopmental data robust when the file stalled on plants and paperwork. Ultragenyx disclosed a complete response letter for UX111 on July 11, 2025. The FDA wanted more chemistry, manufacturing, and controls detail, plus fixes after inspections. The company said the observations were about facilities and process, not the quality of the product in the vial, and that the letter raised no clinical-data problems.

Chief executive Emil D. Kakkis said at the time that the setback would push a possible approval into 2026. The company resubmitted the biologics license application on January 30, 2026. The FDA accepted that filing on April 2, 2026. Approval came on September 17, 2026, two days before the listed action date of September 19, and 14 months after the rejection.

FROM FIRST INFUSION TO A LICENSE

1. May 2016: Eliza O’Neill receives the first human dose of the AAV9 SGSH vector at Nationwide Children’s Hospital.
2. May 2022: Abeona licenses global rights to Ultragenyx, which takes over the Transpher A program.
3. July 11, 2025: Ultragenyx discloses the FDA complete response letter on manufacturing and inspections.
4. January 30, 2026: The company resubmits the biologics license application.
5. April 2, 2026: The FDA accepts the resubmission for review.
6. September 17, 2026: Fayuvi receives standard full approval; a priority review voucher is issued with it.

Fayuvi is made in the United States at Ultragenyx’s gene therapy plant in Bedford, Massachusetts, and at Andelyn Biosciences in Columbus, Ohio, the same city where the first children were dosed. It is the company’s second gene therapy license, after Genglycos for glycogen storage disease type Ia on August 19, 2026, and its sixth FDA approval overall.

The $3.95 Million Shot and Who Pays

Ultragenyx set the U.S. wholesale acquisition cost at $3.95 million per patient. The company has argued that lifetime care for a child with MPS IIIA can run as high as $8 million. That comparison will now go to Medicaid, commercial plans, and hospital budget committees, not to a press release.

THE COMMERCIAL OFFER

• List price: $3.95 million wholesale acquisition cost for a one-time infusion.
• Who is labeled: Pediatric patients with type A and preserved neurodevelopmental function.
• Where it will be given: A U.S. network of Qualified Treatment Centers, not a local pediatric office.
• When it ships: Ultragenyx expects commercial vials ship to treatment centers in 30 to 60 days.

Kakkis said the company’s focus is timely access in the United States while it works with centers and payers, and that a license here is a first step toward reaching families in other countries. UltraCare, the company’s patient program, added gene therapy guides reachable at 888-756-8657 from 9 a.m. to 8 p.m. Eastern Time, Monday through Friday. A product site, fayuvi.com, was slated to go live in the days after approval with the center list.

A one-shot invoice of this size is already the argument around the approval. The counter is the company’s own care-cost figure and the fact that untreated type A still ends in early death. Neither number tells a family whether their child still qualifies, or whether a plan will pay before the remaining skills slip.

Types B, C and D Still Have No Drug

Sanfilippo comes in four autosomal recessive forms. Each is a different enzyme that should break down heparan sulfate. Type A is sulfamidase, the SGSH gene, and now Fayuvi. Type B is alpha-N-acetylglucosaminidase. Type C is heparan acetyl-CoA:alpha-glucosaminide N-acetyltransferase. Type D is N-acetylglucosamine 6-sulfatase. A working SGSH copy does not replace those other enzymes.

Type A is the most common subtype worldwide, though shares shift by region. Combined prevalence for all four types has been estimated between 1 in 50,000 and 1 in 250,000 births, depending on the population. The United Kingdom mortality series found later deaths in type B (mean 18.91 years) and type C (mean 23.43 years) than in type A. Type D was too rare in that set to analyze.

Abeona had also run a type B gene therapy, ABO-101, and a separate study for children with middle to advanced type A, ABT-003, which was stopped in 2022. Those programs are not this license. Families who spent a decade funding “a Sanfilippo drug” now have a type A product with a function test at the door, and three sibling diseases still on supportive care.

What Happens at a Qualified Treatment Center?

Fayuvi is given in a center equipped to handle infusion reactions. Every patient starts corticosteroids one day before the infusion and continues them for at least eight weeks. Vaccines are to be avoided for 30 days before treatment and while steroids continue. Liver tests (ALT, AST, GGT, and bilirubin) and platelet counts are checked before the bag goes up.

LABEL WARNINGS ON FAYUVI

• Liver injury: Raised liver enzymes showed up in 85% of trial patients; steroids are mandatory and labs stay on a schedule until two weeks after the taper.
• Low platelets: Counts are checked weekly for 4 weeks, then monthly for 6 months.
• Clotting injury: Thrombotic microangiopathy is a class risk for AAV products; no Fayuvi trial case was reported, but monitoring is required.
• Infusion reactions: Hypersensitivity and anaphylaxis can occur; the infusion is paused if they do.
• Later cancer risk: AAV DNA can integrate; any malignancy after treatment is to be reported to the company.

The most common other reactions included vomiting (67%), abnormal behavior (56%), diarrhea (48%), and fever (41%). Seizures were listed at 11%. Temporary vector shedding in body fluids and waste lasts 3 months, so caregivers are told to wash hands after contact with urine, stool, or saliva. Women who are pregnant, or who want to become pregnant, are not to be treated, and a negative serum pregnancy test is required in females of childbearing potential.

For a newly diagnosed toddler who still has language and play, the next 30 to 60 days are a race to a Qualified Treatment Center, a payer, and a liver workup. For a teenager who already lost those skills, including some of the children whose early data made the file possible, Thursday’s license does not reopen the trial that dosed them in 2016. Types B, C, and D leave the week as they entered it, with no approved disease-modifying drug.

Frequently Asked Questions

How Is Fayuvi Given, and What Prep Is Required?

It is a single intravenous infusion that takes about an hour in a Qualified Treatment Center. All patients receive corticosteroids starting one day before the infusion and continuing for a minimum of eight weeks, and routine vaccines are held for 30 days before treatment and for the whole steroid course. Liver tests and platelet counts are drawn before the infusion, and platelets are rechecked weekly for the first month.

Does Fayuvi Treat Sanfilippo Types B, C, or D?

No. Fayuvi delivers only the SGSH gene for sulfamidase, the enzyme missing in type A. Types B, C, and D each lack a different enzyme in the same heparan sulfate pathway, so a type A vector cannot correct them. Supportive care remains the licensed option for those subtypes in the United States.

What Is Vector Shedding After a Fayuvi Infusion?

The AAV9 vector can appear for a time in urine, stool, and saliva. The label tells families to use careful hand hygiene after contact with those fluids for 3 months after the infusion. The precaution is about handling waste, not a second treatment course.

Can a Child Receive Fayuvi More Than Once?

The product is labeled as a one-time infusion. The trial that supported approval used a single dose at 3 x 10^13 vector genomes per kilogram, and the prescribing information does not describe a second commercial dose. Prior AAV9 antibodies were a reason children could be kept out of the original study, which is why some families isolated before 2016.

Disclaimer: This article is news reporting and analysis of an FDA approval and related trial and access facts. It is for information only and is not medical advice, a diagnosis, or a treatment recommendation for any child. Families considering gene therapy should consult the child’s metabolic specialist, geneticist, or other qualified physician, and should review the full Fayuvi prescribing information with that clinician before any decision. Figures, eligibility language, prices, and shipping timelines reflect the company, FDA, and foundation sources cited here as of the dates in those documents and may change as centers, payers, and regulators update them.