The U.S. Food and Drug Administration issued a complete response letter (CRL) to Ultragenyx Pharmaceutical, declining approval for its gene therapy UX111 targeting Sanfilippo syndrome Type A, a rare neurodegenerative disorder. The CRL cited manufacturing concerns at Ultragenyx’s facilities, though the FDA did not raise issues over clinical data quality. Ultragenyx plans to address the manufacturing deficiencies and resubmit the application, initiating a new six-month review period. This setback compounds recent challenges for Ultragenyx, including a disappointing phase III data release in a separate program.