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]

Core Insights - REGENXBIO Inc. announced preclinical results showing that a microdystrophin gene therapy construct with the C-terminal (CT) domain provides improved functional benefits for patients with Duchenne Muscular Dystrophy compared to a construct without the CT domain [1][4][5] - RGX-202 is the only investigational microdystrophin gene therapy candidate that includes the CT domain, making it closest to naturally occurring dystrophin [2][8] Group 1: Research Findings - The preclinical study published in Molecular Therapy Methods and Clinical Development demonstrated that the microdystrophin with the CT domain was maintained at higher levels in transduced muscles and effectively recruited the dystrophin-associated protein complex to the muscle membrane [4][5] - The incorporation of the CT domain enhances the microdystrophin design, allowing for higher accumulation levels in muscle and potentially improving functional benefits [5][7] Group 2: Clinical Trial Insights - Interim results from the Phase I/II AFFINITY DUCHENNE trial indicated that RGX-202 showed consistent evidence of positively changing the disease trajectory in patients with Duchenne and had a favorable safety profile [5][6] - REGENXBIO is currently enrolling participants in the pivotal portion of the Phase I/II/III AFFINITY DUCHENNE trial and plans to submit a Biologics License Application (BLA) via the accelerated approval pathway in mid-2026 [6][9] Group 3: Company Overview - REGENXBIO is a biotechnology company focused on gene therapy, with a late-stage pipeline that includes RGX-202 for Duchenne, among other treatments for rare diseases [11] - The company has pioneered AAV gene therapy since its founding in 2009 and has treated thousands of patients with its AAV platform [11]