Regenxbio's Hunter Syndrome Drug Review Delayed by FDA

Regenxbio has announced that the FDA has extended the review date for its Hunter syndrome drug, clemidsogene lanparvovec (RGX-121). The new target action date is now February 8, 2026, which was previously set for November 9, 2025. The FDA's decision will determine whether the drug is approved for marketing.

The U.S. Food and Drug Administration (FDA) has extended the review timeline for clemidsogene lanparvovec (RGX-121), a potential one-time therapy developed by Regenxbio Inc. (Nasdaq: RGNX) to treat Mucopolysaccharidosis II (MPS II), also known as Hunter syndrome. The new target action date has been moved from November 9, 2025, to February 8, 2026 [1].

RGX-121 is designed to deliver the iduronate-2-sulfatase (IDS) gene to the central nervous system (CNS), providing a permanent source of secreted iduronate-2-sulfatase (I2S) protein beyond the blood-brain barrier. This gene therapy aims to address the underlying genetic cause of Hunter syndrome, a rare, X-linked recessive disease that leads to an accumulation of glycosaminoglycans (GAGs) in tissues, resulting in cell, tissue, and organ dysfunction, including in the CNS [2].

The extension follows the submission of longer-term clinical data for all patients in the pivotal study of RGX-121 (n=13) in response to an FDA information request. These data are consistent with previously submitted biomarker and neurodevelopmental data and will be presented during the International Congress of Inborn Errors of Metabolism (ICIEM) in September 2025 [1].

Regenxbio's CEO, Curran M. Simpson, stated that the company promptly provided the FDA with the requested information and expects the commercial launch plans to remain on track. The drug has received multiple designations from the FDA, including Orphan Drug Product, Rare Pediatric Disease, Fast Track, and Regenerative Medicine Advanced Therapy (RMAT) designations, as well as advanced therapy medicinal products (ATMP) classification from the European Medicines Agency [1].

The extension of the review date does not indicate any safety-related concerns, as the FDA completed a pre-license inspection and bioresearch monitoring information inspection for the RGX-121 BLA with no observations [1].

References:
[1] https://www.prnewswire.com/news-releases/regenxbio-announces-fda-review-extension-of-bla-for-rgx-121-to-treat-patients-with-mps-ii-302532620.html
[2] https://seekingalpha.com/news/4486760-regenxbio-says-fda-extends-review-date-for-hunter-syndrome-drug