Ultragenyx Announces U.S. FDA Acceptance of BLA Resubmission for UX111 AAV Gene Therapy to Treat Sanfilippo Syndrome Type A (MPS IIIA)

If approved, UX111 will be the first approved therapy for the treatment of Sanfilippo syndrome Type A, a rare disease affecting young children that leads to progressive, irreversible neurodegeneration and early death

PDUFA action date set for September 19, 2026

NOVATO, Calif., April 02, 2026 (GLOBE NEWSWIRE) -- Ultragenyx Pharmaceutical Inc. (NASDAQ: RARE) today announced the U.S. Food and Drug Administration (FDA or the Agency) 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,” said Emil D. Kakkis, M.D., Ph.D., chief executive officer and president of Ultragenyx. “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.”

During its prior late-cycle review, the FDA acknowledged that the neurodevelopmental outcome data are robust and that the biomarker data provide additional supportive evidence. The updated long-term clinical data included in the BLA and presented at WORLDSymposium 2026 represent up to 8 years of follow-up and show further clinical improvement relative to the decline observed in natural history, and a durable treatment effect across clinical evaluations and multiple biomarkers, while maintaining an acceptable safety profile.

The FDA granted the UX111 BLA Priority Review in February 2025. If approved, UX111 will be manufactured entirely within the U.S., at Andelyn Biosciences in Columbus, Ohio and the Ultragenyx gene therapy manufacturing facility in Bedford, Massachusetts.

About UX111 (rebisufligene etisparvovec)
UX111 (rebisufligene etisparvovec) is a novel in vivo AAV9 gene therapy in Phase 1/2/3 development for Sanfilippo syndrome Type A (MPS IIIA), a rare fatal lysosomal storage disease with no approved treatment that primarily affects the brain. The therapy is designed to address the underlying sulfamidase (SGSH) enzyme deficiency responsible for abnormal accumulation of heparan sulfate (HS), a glycosaminoglycan, in the brain that results in progressive cell damage and neurodegeneration. UX111 is dosed in a one-time intravenous infusion using a self-complementary AAV9 vector to deliver a functional copy of the SGSH gene to cells. These transduced cells then secrete the functional enzyme into the tissue fluid where it can be taken up by surrounding neurons and other cells. The enzyme is taken up efficiently into other cells and is then routed to the lysosome where it can reduce the accumulation of the HS and prevent the progression of lysosomal storage and consequential injury that occurs in untreated patients. The product was originally developed by Abeona Therapeutics and transferred to Ultragenyx to complete development. The UX111 program has received Regenerative Medicine Advanced Therapy, Fast Track, Rare Pediatric Disease, and Orphan Drug designations in the U.S., and PRIME and Orphan medicinal product designations in the EU.