A Phase III Study of JR-141 in Patients With Mucopolysaccharidosis II (STARLIGHT)

Inclusion Criteria: * A patient who voluntarily signs an Institutional Review Board or Independent Ethics Committee-approved written informed consent form. If the patient is aged under 18 years (aged under 16 years in the UK) at the time of enrollment or willingness to participate in the study cannot be confirmed due to MPS II-related intellectual disability, the patient's legally acceptable representative (e.g., his/her parents or guardians) may sign the informed consent on behalf of the patient. Written informed assent should be obtained from the patient, wherever possible. * Patients with confirmed diagnosis of MPS II * Naïve patients or patients who are receiving stable enzyme replacement therapy with idursulfase for more than 12 weeks before starting administration of JR-141 or idursulfase for this study. * Patients or patients whose partners are of child-bearing potential agree to use a medically accepted, highly effective method of contraception being use of condoms from the time of informed consent. \<Cohort A\> * Patients aged 36-42 months old at the time of ICF signing: patients must have a standard score measured by the BSID-III of 85 or less at screening. * Patients aged 43-71 months old at the time of ICF signing: patients must EITHER have (1) A DQ measured by BSID-III of 20 to 85 at screening OR (2) A composite standard score on NVI measured by KABC-II of 85 or less at screening (only who can perform KABC-II) * Patients aged 30-35 months old at the time of ra…