Ultragenyx resubmitted its biologics license application for UX111, an AAV gene therapy candidate for Sanfilippo syndrome type A, after the FDA rejected the original filing last summer. The resubmission signals Ultragenyx’s intent to address agency concerns and keep the rare‑disease program on a regulatory path. The company did not disclose all changes in the resubmission but positioned UX111 as a renewed effort to deliver a one‑time gene therapy for a progressive neurodegenerative pediatric disorder. Sponsors often resubmit with additional analyses, manufacturing updates or new clinical data to resolve prior deficiencies. For rare‑disease developers and investors, the re‑filing highlights the iterative regulatory path for complex AAV products and the importance of early CMC alignment and robust durability/safety datasets to secure approval for pediatric gene therapies.