A promising gene therapy for Sanfilippo syndrome—a relentless disease that robs children of speech, mobility, and independence—is stalled by FDA delays. Trials show UX111 can slow or preserve these abilities, offering hope where no treatments exist.

Yet despite strong data, approval was rejected over minor manufacturing issues, delaying access for at least 6–12 months. For children with Sanfilippo, every month means irreversible loss.

Our kids are losing their voices, so we need yours to help by contacting HHS Secretary Kennedy and FDA Commissioner Makary and ensure:

• Swift review of resubmissions for rare disease drugs, especially for Sanfilippo and Barth.

• Engagement with sponsors to resolve minor issues before rejecting applications.

• The FDA holds direct meetings with patient communities impacted by recent delays, including Sanfilippo and Barth.

• The FDA makes full use of existing regulatory flexibility when the science is strong and safety risks are minimal.

Update as of 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."

Read Ultragenyx's initial press release about the resubmission

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