The FDA has granted priority review for Ultragenyx Pharmaceutical's gene therapy UX111, aimed at treating Sanfilippo syndrome type A, with a decision anticipated by mid-August 2025.

This priority review shortens the review period for the biologics license application from 10 months to just 6 months, potentially accelerating the approval process.

Previously, the FDA recognized UX111 with rare pediatric disease and orphan drug designations, which have facilitated its development.

The ongoing Phase 1/2/3 Transpher A clinical trial, involving 28 children, has shown promising preliminary results, including significant reductions in heparan sulfate (HS) levels and improvements in cognitive function.

UX111 works by addressing the toxic buildup of heparan sulfate in the brain, which is known to damage brain cells.

The therapy introduces a functional copy of the SGSH gene through a viral vector via intravenous infusion, aiming to restore the breakdown of HS and slow neurodegeneration.

Initial results from the trial indicated that HS levels dropped significantly within the first month of treatment, with most participants maintaining or improving their cognitive function over nearly 2.5 years.

The most common side effect reported among participants was elevated liver enzymes, which were generally mild to moderate.

Ultragenyx has established a clear path forward with the FDA for accelerated approval, indicating strong regulatory support for the development of UX111.

Emil D. Kakkis, CEO of Ultragenyx, expressed optimism that UX111 could become the first treatment for Sanfilippo syndrome type A, with plans in place for a patient launch upon approval.