FDA Declines to Approve Regenxbio's Hunter Syndrome Treatment

By Amira McKee

The Food and Drug Administration has declined to approve Regenxbio's gene therapy, RGX-121, for the treatment of Hunter syndrome, a rare and fatal neurodegenerative disease.

The clinical-stage biotechnology company said Monday that the FDA agreed to the study protocol in principle and outlined several reasons for not approving the gene therapy.

In a complete response letter regarding Regenxbio's biologics license application, the FDA questioned if the study properly identified the right patient groups, whether the historical data used for comparison was accurate, and if the biological markers measured in spinal fluid were strong enough evidence to predict actual health benefits for the patients. The FDA accepted the RGX-121 biologics license application under the accelerated approval pathway in May 2025.

Regenxbio said it plans to find a path forward as quickly as possible with the goal of resubmitting its biologics license application.

"We are concerned about FDA's feedback regarding the overall development path and evaluation of the data in the context of the urgent need for this irreversible ultra-rare disease," said Curran Simpson, chief executive officer of Regenxbio. "We remain confident in the quality and volume of evidence demonstrating the long-term potential of RGX-121 to positively change the trajectory of Hunter syndrome.

Write to Amira McKee at amira.mckee@wsj.com

(END) Dow Jones Newswires

February 09, 2026 17:03 ET (22:03 GMT)