REGENXBIO Announces FDA Review Extension of BLA for RGX-121 to Treat Patients with MPS II

Core Viewpoint - REGENXBIO Inc. announced an extension of the FDA review timeline for its Biologics License Application (BLA) for RGX-121, a treatment for Mucopolysaccharidosis II (MPS II), from November 9, 2025, to February 8, 2026 [1] Group 1: FDA Review and Clinical Data - The extension follows the submission of long-term clinical data for all patients in the pivotal study of RGX-121, which included 13 patients, in response to an FDA information request [2] - Positive 12-month clinical data are consistent with previously submitted biomarker and neurodevelopmental data and will be presented at the International Congress of Inborn Errors of Metabolism (ICIEM) in September 2025 [2] - The FDA completed a pre-license inspection and bioresearch monitoring inspection for the RGX-121 BLA with no observations and no safety-related concerns raised during the review [3] Group 2: Company Statements and Designations - The President and CEO of REGENXBIO emphasized the urgent need for a therapeutic option for boys with Hunter syndrome and expressed confidence that commercial launch plans remain on track [4] - RGX-121 has received multiple designations from the FDA, including Orphan Drug Product, Rare Pediatric Disease, Fast Track, and Regenerative Medicine Advanced Therapy (RMAT) [4] Group 3: Product and Disease Overview - RGX-121 is a potential one-time AAV therapeutic designed to deliver the iduronate-2-sulfatase (IDS) gene to the central nervous system, potentially providing a permanent source of the I2S protein [5] - MPS II, or Hunter Syndrome, is a rare disease caused by a deficiency in the lysosomal enzyme I2S, leading to significant medical needs, particularly for neurological manifestations [6] Group 4: Future Plans and Market Potential - If approved, RGX-121 would be the first and only commercially available therapy designed to address the underlying genetic cause of Hunter syndrome [8] - REGENXBIO plans to present updated pivotal data during the ICIEM meeting in September 2025 [8]