UX111 (rebisufligene etisparvovec) for Sanfilippo syndrome type A (MPS IIIA)
The FDA is expected to decide on UX111 for Sanfilippo syndrome type A (MPS IIIA) by September 19, 2026, under a BLA resubmission from Ultragenyx.
What is being decided
Ultragenyx has a BLA resubmission under FDA review for UX111 (rebisufligene etisparvovec) in Sanfilippo syndrome type A (MPS IIIA). Would be the first approved treatment in the history of Sanfilippo syndrome. The FDA rejected UX111 in 2025 on manufacturing grounds unrelated to efficacy.
Who this decision matters to
Mucopolysaccharidosis Type III (MPS III, Sanfilippo Syndrome) is a lysosomal storage disorder caused by deficiency of enzymes required to break down heparan sulfate. This leads to accumulation of heparan sulfate primarily in the brain, causing progressive neurodegenerative disease with behavioral changes, cognitive decline, and loss of motor skills. MPS III is characterized by relatively mild somatic features but severe and progressive neurological involvement.
Prevalence: Approximately 1 per 70,000 to 1 per 100,000 live births; highest prevalence in certain populations including Australia and Scandinavia. See our full Mucopolysaccharidosis Type III page for current treatments, recruiting trials, and community resources.
What each outcome would mean
An approval starts a second race rather than ending the first one: specialty pharmacy setup, insurance review, and patient assistance typically take weeks even when everything goes right. Our guide to the 90 days after a rare disease approval explains the timeline and the moves families can make on day 1.
A complete response letter would mean the FDA declined to approve in the application's current form. CRLs are often about manufacturing or data presentation rather than efficacy, and resubmission is common. Either way, this page updates with the outcome and what it means.
Where Mucopolysaccharidosis Type III treatment stands today
Research in Mucopolysaccharidosis Type III addresses the progressive neurodegeneration that characterizes this disease through enzyme replacement, substrate reduction, gene therapy, and supportive approaches. Because different subtypes have distinct genetic bases, trials may focus on specific subtypes. Early intervention before or very early in cognitive decline shows the greatest promise for slowing neurological progression. Gene therapy trials are working to achieve enzyme expression in the central nervous system using innovative vectors that cross the blood-brain barrier. Beyond disease-modifying approaches, trials are also exploring strategies to manage the behavioral problems, sleep disturbances, and neurodegeneration that affect quality of life. Monitoring biomarkers including heparan sulfate levels in urine and cerebrospinal fluid helps track disease progression and treatment response. Consultation with pediatric neurology specialists experienced in lysosomal disorders helps identify appropriate interventions.
Meanwhile, 11 Mucopolysaccharidosis Type III trials are recruiting
Whatever the FDA decides here, research on Mucopolysaccharidosis Type III does not stop. A few currently enrolling studies, US sites first:
Get notified when new mucopolysaccharidosis-type-iii trials open or existing trials change status, add sites, or update eligibility.
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Frequently asked questions
When will the FDA decide on UX111?
The FDA's target decision date (PDUFA date) for UX111 in Sanfilippo syndrome type A (MPS IIIA) is September 19, 2026, disclosed by Ultragenyx. The agency can act before this date and occasionally runs past it.
What is UX111 being reviewed for?
Ultragenyx submitted a BLA resubmission for UX111 in Sanfilippo syndrome type A (MPS IIIA). Would be the first approved treatment in the history of Sanfilippo syndrome. The FDA rejected UX111 in 2025 on manufacturing grounds unrelated to efficacy.
What happens after the UX111 decision?
If approved, availability is not immediate: specialty pharmacy setup, insurance review, and patient assistance typically take weeks even when everything goes right. If the FDA issues a complete response letter, the application was not approved in its current form; CRLs are often about manufacturing or data presentation rather than efficacy, and sponsors frequently resubmit. This page updates with the outcome either way.
Where this date comes from
The FDA does not publish PDUFA dates; companies disclose them. This one comes from Ultragenyx press release. Dates can move, and the FDA can act early or late. This page rechecks against our calendar, which is re-verified weekly.