RARE Stock Slips 3% Today — What’s Up With Ultragenyx’s Gene Therapy For Sanfilippo Syndrome?

• Ultragenyx now expects a 6-month review period for the therapy and a likely decision from the FDA regarding potential approval by the third quarter of 2026.
• The FDA refused to approve the company’s application for the drug in July, and issued a letter requesting Ultragenyx to provide more information.
• However, no date has been officially provided by the agency.

Shares of Ultragenyx Pharmaceutical Inc. (RARE) fell 3% on Friday after the company said that it has submitted an application to the U.S. Food and Drug Administration (FDA) regarding a drug previously refused approval.

The company said that it has resubmitted an application for UX111 gene therapy as a treatment for patients with Sanfilippo syndrome type A.

Fresh Submission Details

The fresh submission includes substantial longer-term data on multiple measures of neurologic benefit as well as additional long-term clinical data from current patients, the company said.

It also includes responses to the observations raised by the FDA in a letter to the company in July, Ultragenyx added.

Sanfilippo syndrome type A is a severe, progressive genetic disorder caused by a deficiency in the sulfamidase enzyme, leading to the buildup of heparan sulfate in cells, primarily damaging the brain and nervous system. Children with the disorder present with global developmental delay, which eventually leads to progressive cognitive, language and motor decline, behavioral abnormalities, and early death.

Previous Application

The FDA refused to approve the company’s application for the drug in July, and issued a letter requesting Ultragenyx to provide more information and improvements related to specific aspects of  chemistry, manufacturing, and controls as well as observations from inspections of its manufacturing facility. The company then said it is working with the agency to resolve the observations.

Ultragenyx now expects a 6-month review period for the therapy and a likely decision from the FDA regarding potential approval by the third quarter of 2026. However, no date has been officially provided by the agency yet.

If approved, UX111 will be the first approved therapy for Sanfilippo syndrome type A, the company said.

How Did Stocktwits Users React?

On Stocktwits, retail sentiment around RARE stock stayed within the ‘bearish’ territory over the past 24 hours while message volume remained at ‘extremely low’ levels.

RARE stock fell by 46% over the past 12 months. 

Also See: Dan Ives Says AI Will Drive Apple’s 2026 Story As iPhone Price Hikes Linger: Report

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