Ultragenyx Tanks After Rare Gene Therapy Bounced by FDA, Citing Manufacturing Problems

While taking on rare diseases might be in Ultragenyx’sRARE

DNA, it appears manufacturing meds doesn’t come so second nature. After reporting solid data for a promising new pediatric gene therapy, US regulators ultimately declined to approve the treatment — citing manufacturing process concerns.

• The FDA issued a complete response letter (CRL) for UX111, requesting “additional information and improvements” from its manufacturing facilities and processes.
• Ultragenyx holds that the firm would work with the FDA to resolve its concerns, then resubmit the drug for review — the regulator acknowledged the drug’s promising data.

So what? CRLs on gene therapies are increasingly common, with the FDA declining to approve many revolutionary treatments on similar concerns about manufacturing and process quality. The outlay? No treatment option for patients with Sanfilippo syndrome type A (MPS IIIA), a serious and fatal disease.RARE

has fallen 34% since the news. However, with strong data in the tank, the company hopes to get the one-time treatment resubmitted — and approved to save the lives of thousands of patients in 2026.