An extension of Global Phase III open-label, multicenter designed to evaluate the Long-term safety and efficacy of study drug for the treatment of the MPS II.

Inclusion Criteria:

1. A subject who participated in the Parent Study (JR-141-GS31) and completed the assessments at Week 105 in Cohort A or Week 53 in Cohort B before being administered the study medication of that respective visit, and in the opinion of the principal investigator there are no safety concerns.
2. A subject from whom an IRB or IEC-approved written informed consent can be obtained, which is voluntarily signed. If the subject 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 subject's legally acceptable representative (e.g., his parents or guardians) may sign the ICF on behalf of the subject. Written informed assent should be obtained from the subject, wherever possible.
3. Female subject of child bearing potential or male subject whose female partner is of child-bearing potential, i.e., fertile, following menarche and until becoming post-menopausal unless permanently sterile, agrees to use a medically accepted, highly effective method of contraception from the time of signing the ICF. The method of contraception must be used during the study until 90 days for male subjects, and 30 days for female subjects after the final study drug administration.

Exclusion Criteria:

1. A subject who changed treatment from JR-141 to idursulfase during the treatment period in the Parent Study (JR-141-GS31).
2. A subject who is unable to comply with the protocol (e.g., is unable to return for safety evaluations or is otherwise unlikely to complete the study) as determined by the principal investigator or sub-investigator.
3. [Only in France] Persons deprived of their liberty by a judicial or administrative decision, according to article L. 1121-6 of the Public Health Code (Code de la santé publique, CSP) adults who are the subject of a measure of legal protection or unable to express their consent according to article L. 1121-8 of the CSP.