Three days to UX111

In Short. Ultragenyx’s resubmitted BLA for UX111 (rebisufligene etisparvovec) in Sanfilippo syndrome type A still carries a Prescription Drug User Fee Act action date of September 19, 2026, per the company’s April 2, 2026 Form 8-K. A PDUFA date is a decision calendar. The product, the disease, and which ClinicalTrials.gov records actually belong to that package have to be named before any endpoint claim.

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Sanfilippo syndrome type A, or mucopolysaccharidosis IIIA, is a rare genetic lysosomal storage disease of childhood. Children lack enough of the enzyme sulfamidase, encoded by SGSH, so heparan sulfate glycosaminoglycans build up and the brain is progressively damaged. There is still no approved disease-modifying therapy for MPS IIIA in the United States. That empty shelf is why a posted FDA action date three days away is a clinic clock rather than a vague rare-disease headline.

UX111, also known as ABO-102 and as rebisufligene etisparvovec, is Ultragenyx’s one-time AAV9 gene therapy meant to deliver a working SGSH copy. On April 2, 2026, Ultragenyx filed an 8-K (accession 0001193125-26-139084) stating that FDA had accepted for review the company’s resubmitted Biologics License Application seeking accelerated approval of UX111 for Sanfilippo syndrome Type A, and that FDA set a PDUFA action date of September 19, 2026. That filing is a primary for the calendar. Today’s Synbiomatica regulatory packet still lists the same date as Upcoming, three days out.

A decision date is only as useful as the package it points to. Here the free regulatory feed needs a correction before any reader trusts a nested trial ID. The packet row for UX111 nests NCT03517085 as completed. Opening that record on ClinicalTrials.gov shows a completed Ultragenyx Phase 1/2 study of DTX401 (AAV8-G6PC) in adults with glycogen storage disease type Ia, with actual primary completion on November 2, 2021. That is a different enzyme, a different organ emphasis, and a different disease. The nested NCT is a feed fact about an Ultragenyx gene-therapy file. It is the wrong spine for a Sanfilippo A PDUFA.

The studies that actually name UX111 or ABO-102 for MPS IIIA on today’s registry are elsewhere. NCT02716246 is a Phase 2/3 gene-transfer trial of scAAV9.U1a.hSGSH in MPS IIIA, still listed RECRUITING, estimated enrollment 36, last update August 21, 2026. The intervention is listed as UX111. Its primary outcome on the live record is cerebrospinal fluid heparan sulfate (disaccharide) exposure, defined as the time-normalized area under the curve of the percentage reduction from baseline, through the Month 24 visit. Estimated primary completion is March 2029. That registry primary is what the public trial record currently shows. It is not, by itself, a verified table of what FDA will treat as substantial evidence inside the closed BLA.

Two neighbor records round out the public UX111/ABO-102 cluster without replacing that spine. NCT04360265 is a long-term follow-up for patients from prior ABO-102 / UX111 gene-therapy trials, enrolling by invitation, with safety and Bayley cognitive scores among its primaries. NCT04088734 is a terminated ABO-102 study in middle and advanced MPS IIIA, with results posted, whose primaries were safety, liver and spleen volumes, and CSF heparan sulfate levels. Those records explain how the program appears on ClinicalTrials.gov. They do not automatically equal the confidential review file FDA will act on September 19.

What September 19 decides, on the company’s own 8-K language, is whether FDA will grant accelerated approval of the resubmitted UX111 BLA for Sanfilippo A. Accelerated approval is a legal pathway that can rest on an intermediate clinical endpoint reasonably likely to predict clinical benefit, with confirmatory work still owed afterward. The April 2 filing states the acceptance and the PDUFA date. It does not reprint the Agency’s review memo, the full endpoint hierarchy FDA accepted, or chemistry-manufacturing responses from any earlier complete response letter. Those documents were not opened for this draft.

Drugs@FDA / openFDA queries for UX111, ABO-102, and Ultragenyx brand products returned no matching application-number row in this run, which is expected for an unapproved BLA still under review. The numeric application ID stays unverified. The closed BLA’s exact evidentiary weight stays unverified until a decision letter or a label exists to quote.

On September 19 the calendar either produces an approval, a complete response, or another deferral. The disease and the product stay the same either way. The feed’s wrong NCT does not.