What is happening?
On February 12, 2026 Ultragenyx received an Incomplete Response Letter from the FDA which requested additional supportive documentation around the Chemistry, Manufacturing,and Controls (CMC) portion of the UX111 Sanfilippo A gene therapy submission. Ultragenyx plans to provide the additional documents to the FDA as quickly as possible and will then resubmit their BLA for accelerated approval.
"One year has passed since the original BLA submission. Our children with Sanfilippo syndrome have suffered an additional year of neurologic injury. Heartbreakingly, setbacks like these have real consequences for children and families," said Cure Sanfilippo Foundation President Glenn O'Neill. "We remain hopeful that the U.S. Food and Drug Administration will honor its commitment to accelerate approvals of treatments for rare, fatal pediatric diseases like Sanfilippo syndrome."
