FDA Extends PDUFA Date for Regenxbio’s Hunter Syndrome Gene Therapy RGX-121

The FDA has pushed back the PDUFA (Prescription Drug User Fee Act) date for Regenxbio's Hunter syndrome gene therapy, clemidsogene lanparvovec (RGX-121), from November 9, 2025, to February 8, 2026135.

The extension followed an FDA request for 12-month clinical data from 13 patients in RGX-121's pivotal trial, which Regenxbio provided, with results consistent with prior biomarker and neurodevelopmental data submitted for those patients13.

The FDA has completed pre-license and bioresearch monitoring inspections for RGX-121 with no objections or safety concerns reported1.

RGX-121 is a one-time gene therapy designed to deliver a functional copy of the iduronate-2-sulfatase (IDS) gene to the central nervous system, aiming to address neurological decline in boys with Hunter syndrome (Mucopolysaccharidosis II)13.

Hunter syndrome is a rare lysosomal storage disorder caused by IDS gene deficiency, leading to the harmful buildup of certain sugars in cells and resulting in organ damage and loss of brain function134.

Regenxbio’s therapy has received multiple regulatory designations including orphan drug, rare pediatric disease, fast track, and RMAT (Regenerative Medicine Advanced Therapy) from the FDA4.

While the FDA review extension delays potential market entry, it is seen as a move to ensure robust clinical evidence, reflecting both regulatory rigor and the need for innovative therapies in rare diseases3.

Sources:

1. https://www.fiercebiotech.com/biotech/fda-pushes-back-pdufa-date-regenxbios-hunter-syndrome-gene-therapy

3. https://www.ainvest.com/news/regenxbio-fda-review-extension-rgx-121-implications-gene-therapy-commercialization-2508/

4. https://www.cellgenetherapyreview.com/3972-News/619415-Regenxbio-MPS-II-gene-therapy-gets-priority-review-November-PDUFA-date/

5. https://www.ainvest.com/news/regenxbio-rgx-121-review-timeline-extended-fda-2508/