Separate from the headline approval coverage, the approval narrative reflects the tight link between FDA scrutiny and manufacturing quality for gene therapies. The Fayuvi decision follows a prior FDA refusal, in which the agency pointed to concerns about Ultragenyx’s manufacturing process for the AAV-based product. That earlier setback is notable for gene therapy developers: even when clinical data are strong, regulatory review can hinge on process controls, product consistency, and the ability to reliably manufacture across commercial timelines. The new approval closes a four-year gap since the company’s earlier application and puts Ultragenyx at the center of the rare-disease gene therapy market with a first-of-its-kind indication in MPS IIIA. Clinicians and payers will now focus on real-world implementation questions, including patient selection, durability of expression, and outcomes across the labeled population.