The purpose of this study in patients with mucopolysaccharidosis type II (MPS II) is below,

• to collect the safety information of JR-141
• to evaluate the plasma pharmacokinetics of JR-141
• to explore the efficacy of JR-141 on MPS II-related central nervous system symptoms and general symptoms

Inclusion Criteria:

• Patients aged 6 years or older at the time of informed consent.
• Patients diagnosed with MPS II.
• Patients who have received idursulfase (0.5 mg/kg/week) continuously for at least 12 weeks until the initial dose of JR-141.

Exclusion Criteria:

• Patients with a history of hematopoietic stem cell transplantation, excluding those who need enzyme replacement therapy even after hematopoietic stem cell transplantation.
• Patients in whom lumbar puncture cannot be performed.
• Patients who have developed serious drug allergy or hypersensitivity that is inappropriate for participation in the study.
• Patients who have received other investigational products within 4 months before enrollment in the study.