RGX-121 is a clinical-stage drug being developed for the treatment of Mucopolysaccharidosis type II (MPS II/ Hunter syndrome) is a rare, X-linked recessive lysosomal storage disorder caused by deficiency of the iduronate-2-sulfatase (IDS) enzyme. The disease affects approximately 0.70 per 1,000,000 individuals and occurs in about 1 in 385,000 live births, with the majority of affected individuals being male (1). MPS II imposes a substantial clinical burden, as patients develop progressive multi-organ dysfunction involving the cardiovascular, hepatic, respiratory, and skeletal systems and, in many cases, the central nervous system (CNS), including the brain and spinal cord. These manifestations lead to reduced life expectancy and markedly impaired quality of life.. It is being developed by Regenxbio, Inc.. The FDA Prescription Drug User Fee Act (PDUFA) date is February 8, 2026. Premium analysis including detailed clinical trial status, revenue predictions, and comprehensive company insights are available for members.