REGENXBIO Announces Regulatory Update on Ultra Rare MPS Programs

Core Viewpoint - REGENXBIO Inc. has announced that the FDA has placed a clinical hold on its investigational gene therapies RGX-111 and RGX-121 due to a case of neoplasm identified in a participant treated with RGX-111, raising concerns about the safety of both therapies [1][2]. Group 1: Clinical Hold Details - The FDA's clinical hold on RGX-111 and RGX-121 is based on a single case of an intraventricular CNS tumor found in a five-year-old participant who received RGX-111 four years prior [1][2]. - Preliminary genetic analysis of the tumor indicated an AAV vector genome integration event linked to overexpression of the proto-oncogene PLAG1, which is associated with chromosomal rearrangements [2]. Group 2: Company Response - REGENXBIO expressed surprise at the FDA's decision to place RGX-121 on hold, emphasizing that RGX-121 has a positive safety profile based on data from over 30 patients treated [3]. - The company highlighted the urgent medical need for RGX-121 in treating MPS II, stating that delays could lead to neurodevelopmental decline in affected patients [3]. Group 3: Therapy Information - RGX-121 is a one-time gene therapy designed to deliver the iduronate-2-sulfatase (IDS) gene to the CNS, potentially providing a permanent source of the I2S protein beyond the blood-brain barrier [4]. - RGX-111 aims to deliver the alpha-L-iduronidase (IDUA) gene to the CNS, which could help prevent cognitive deficits in MPS I patients [7]. Group 4: Disease Background - MPS II, or Hunter Syndrome, is a rare disease caused by a deficiency in the lysosomal enzyme I2S, leading to the accumulation of glycosaminoglycans and resulting in dysfunction across various tissues, including the CNS [6]. - MPS I is a rare genetic disease caused by a deficiency in the enzyme IDUA, leading to similar accumulations and dysfunctions, with an estimated occurrence of 1 in 100,000 births [9].