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Big news: UX111 has been approved!
Big news: UX111 has been approved!
Update as of September 17, 2026
Update as of September 17, 2026
FDA approves first-ever treatment for Sanfilippo Syndrome Type A, FAYUVI™
On September 17, 2026, the U.S. Food and Drug Administration (FDA) granted standard full approval of FAYUVI™ (rebisufligene etisparvovec-hopf), also known as UX111, for the treatment of pediatric patients with mucopolysaccharidosis type IIIA (MPS IIIA, Sanfilippo syndrome Type A).
FAYUVI is the first-ever FDA-approved treatment for Sanfilippo syndrome Type A, a progressive and fatal neurodegenerative disease.
“For families living with Sanfilippo syndrome type A, the trajectory of this disease is heartbreaking — children who develop normally in their earliest years facing a relentless regression with no approved treatment to slow it. Parents and clinicians have been waiting far too long for an option,” said Karim Mikhail, B. Pharm., M.S., Director of the Center for Biologics Evaluation and Research in FDA’s announcement. “Today’s approval of Fayuvi is a meaningful step forward — not only for these children and their families, but for the promise of gene therapy to address rare and devastating diseases where the need for safe and effective treatment is the most urgent.”
Steps to Explore Treatment
Steps to Explore Treatment
Talk with your child's clinician
Start by discussing whether gene therapy may be appropriate for your child with your clinician.Connect with UltraCare
With support from your child's clinician, you may choose to enroll in the Ultragenyx patient services program, UltraCare, which can help with:Understanding insurance coverage
Financial assistance eligibility
Logistical support before and after treatment
Get referred to a Qualified Treatment Center (QTC)
If appropriate, your child's clinician may refer you to a Qualified Treatment Center, a specialized center with expertise in gene therapy. A QTC provider would prescribe and administer the treatment.
What was happening?
What was happening?
A promising gene therapy for Sanfilippo syndrome—a relentless disease that robs children of speech, mobility, and independence—was stalled by FDA delays. Trials show UX111 can slow or preserve these abilities, offering hope where no treatments exist.
Yet despite strong data, approval was rejected over minor manufacturing issues, delaying access for at least 6–12 months. For children with Sanfilippo, every month means irreversible loss.
Update as of April 2, 2026
Update as of April 2, 2026
Ultragenyx announced the U.S. Food and Drug Administration has accepted for review the resubmitted Biologics License Application (BLA) seeking accelerated approval for UX111 (rebisufligene etisparvovec) AAV9 gene therapy as a treatment for patients with Sanfilippo syndrome Type A (MPS IIIA). The FDA set a Prescription Drug User Fee Act (PDUFA) action date of September 19, 2026.
“The FDA’s acceptance of the BLA for UX111 brings us closer to the possibility of a first-ever therapy for Sanfilippo syndrome Type A—a milestone that we recognize cannot come soon enough for families facing this devastating diagnosis. We appreciate the FDA’s prompt acceptance of the resubmission and look forward to working with the Agency throughout its review in order to bring this treatment option to the Sanfilippo syndrome community as quickly as possible.” said Emil D. Kakkis, M.D., Ph.D., chief executive officer and president of Ultragenyx.
- Emil D. Kakkis, M.D., Ph.D., chief executive officer and president of Ultragenyx
Update as of February 26, 2026
Update as of February 26, 2026
Cure Sanfilippo Foundation Chief Science Officer Cara O’Neill, MD, was among four expert witnesses testifying before the U.S. Senate Special Committee on Aging to explore how U.S. Food and Drug Administration processes and evolving standards unintentionally delay patient access to safe and effective therapies, particularly for individuals living with rare diseases.
“Congress has given FDA the tools of flexibility it needs to accelerate approvals for these devastating diseases. But sadly, flexibility and speed are not actually what most rare disease patients are witnessing. Transformative therapies are at FDA's doorstep. And so with great respect, families are pleading for FDA to unlock the door and move with urgency so that our children can have a chance at the life they deserve.”
- Dr. Cara O’Neill, Chief Science Officer and Co-Founder, Cure Sanfilippo Foundation, and mother of Eliza (age 16)
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About Sanfilippo Syndrome
About Sanfilippo Syndrome
Sanfilippo Syndrome is a terminal, degenerative disease that causes children to lose all the skills they’ve gained, suffer seizures and movement disorders, experience pain and suffering, dementia, and then die usually in their teen years. It is often referred to as being like a late-stage Alzheimer’s, but in children.
Sanfilippo is a rare genetic disease. Parents are unknowingly carriers of a genetic mutation that causes the children to have this condition. It is estimated that 1 in 70,000 births result in Sanfilippo. This equates to many thousands around the world suffering from this disease. Because it is rare, it is often left to parent-led organizations to spread awareness and fund research.
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