FDA issues complete response letter for UX111, citing manufacturing and facility observations

Ultragenyx/Fayuvi (UX111)

The FDA declined to approve UX111 for Sanfilippo syndrome type A for now, pointing to chemistry, manufacturing and controls issues found during facility inspections. It raised no concerns about the clinical results and called the neurodevelopmental data robust. Ultragenyx planned to fix the issues and resubmit, expecting up to six months of review.

• Issues concerned facilities and processes, not the quality of the product, the company said.
• The FDA described the clinical outcome data as robust, with biomarker data as support.
• Resubmission expected to trigger a review of up to six months, pushing approval into 2026.