 ROCKVILLE, Md., May 14, 2021 PRNewswire -- RGX-121, a one-time gene therapy for MPS II, continues to be well-tolerated with no drug-related serious adverse events Biomarkers and measures of neurodevelopmental function from patients in Cohorts 1 and 2 continue to indicate CNS activity following RGX-121 administration Evidence of systemic enzyme expression and biomarker activity continues to be observed REGENXBIO recently initiated dosing of patients in Cohort 3 REGENXBIO Inc. Nasdaq: RGNX today announced a safety update and additional positive interim data from the ongoing Phase III trial of RGX-121 for the treatment of patients up to 5 years old diagnosed with Mucopolysaccharidosis Type II MPS II, also known as Hunter Syndrome. 