Ultragenyx Pharmaceutical has encountered a regulatory setback as the FDA issued a complete response letter (CRL) for its gene therapy UX111 aimed at treating Sanfilippo syndrome type A, a rare neurodegenerative disorder. The FDA's concerns center on manufacturing processes at the company's production facility, although the issues are not related to product quality. Ultragenyx plans to address the manufacturing deficiencies and resubmit the therapy for approval, initiating a new six-month review period. This marks another challenge for Ultragenyx following recent clinical trial disappointments. Analyst commentary suggests the CRL represents a temporary delay rather than a rejection of the therapy's efficacy.