The purpose of this study is to find out if JR-141, an experimental drug, works better than the standard treatment, idursulfase, for MPS II (Hunter Syndrome) and how safe and effective it is in the management of central nervous system symptoms (such as brain or body function loss) and other body symptoms (including lungs, ears, heart, kidneys, and eyes, as well as any type of liver, bone or joint abnormalities) related to MPS II. Since JR-141 is an investigational drug, it has not been approved by the Food and Drug Administration (FDA).