12-month pivotal data further demonstrate the ability of one-time RGX-121 treatment to improve outcomes for patients with MPS II >80% reduction in CSF levels of HS D2S6, key biomarker of MPS II brain disease, sustained through 1 year Pivotal patients demonstrate continued skill acquisition or stability, stratified by baseline function, through 1 year Primary endpoint of CSF HS D2S6 reduction at week 16 met; strong correlation to neurodevelopmental outcomes at 1 year, supporting HS D2S6 as surrogate bioma ...