 ROCKVILLE, Md., April 14, 2021 PRNewswire -- First patient dosed at third dose level in ongoing trial of RGX-121, a one-time gene therapy for MPS II; total of nine patients have been dosed at four leading clinical centers in the U.S. and Brazil Previously reported positive interim data from Cohorts 1 and 2 demonstrated consistent reductions in CNS biomarkers, continued neurocognitive development, and evidence of systemic effects REGENXBIO Inc. Nasdaq: RGNX today announced that it dosed the first patient in Cohort 3 of the ongoing Phase III trial of RGX-121 for the treatment of Mucopolysaccharidosis Type II MPS II, also known as Hunter Syndrome, in patients up to five years old. 