The FDA issued a complete response letter declining approval of Ultragenyx’s gene therapy UX111 for Sanfilippo syndrome Type A, citing manufacturing process issues. The regulatory setback arises weeks before an August decision deadline, though the FDA did not challenge clinical data quality. Ultragenyx intends to rectify manufacturing concerns and resubmit, resetting the six-month review clock. Analysts frame the FDA’s decision as a temporary delay rather than a roadblock, amid the therapy’s potential near-term commercial impact and priority review voucher prospects.