Ultragenyx Pharmaceutical received a complete response letter from the FDA due to manufacturing process concerns for its gene therapy UX111 targeting Sanfilippo syndrome type A. While the agency’s objections are related to Chemistry, Manufacturing, and Controls (CMC) rather than product quality or clinical data, the company acknowledged the issues and intends to address them and resubmit for approval. This setback follows recent clinical disappointments, yet analysts view it as a temporary hurdle rather than a permanent barrier. Ultragenyx plans additional data submissions including updated results from ongoing studies and is expecting to restart a six-month review clock upon resolution.