Ultragenyx resubmitted its biologics license application for UX111, an AAV gene therapy targeting Sanfilippo syndrome type A, following an earlier FDA rejection. The resubmission restarts the agency review process and keeps a rare‑disease gene therapy on the regulatory calendar. Sponsors in the AAV space now face renewed focus on long‑term safety, manufacturing comparability and class‑specific risks as regulators reassess previously rejected submissions and decide on data sufficiency for approval.