The FDA has suspended studies of two experimental gene therapies from Regenxbio after a brain tumor was found in one child. These are therapies being developed for rare diseases, including Duchenne muscular dystrophy (DMD) and Hunter syndrome (MPS II). A patient treated with RGX-202 therapy for DMD experienced this serious adverse event. The AFFINITY DUCHENNE study for RGX-202 showed improvement in 4 patients on the NSAA scale at 18 months versus expected disease progression. For RGX-121 (clemidsogene lanparvovec) for MPS II, the FDA extended BLA review to February 8, 2026 with no reported safety concerns. 13 patients in the pivotal study experienced an 82% reduction in CSF heparan sulfate HS D2S6 levels at 1 year. RGX-121 therapy delivers a functional iduronate-2-sulfatase gene to the central nervous system for long-term repair.