Multicenter, open-label, single-group, designed to evaluate the long term efficacy and safety of study drug for the treatment of the MPS II.

Inclusion Criteria:

1. A patient who participated in the preceding Study JR-141-301 and completed the Week 52 visit, and has no safety concerns to enter this study in the opinion of the investigator or subinvestigator.
2. A patient capable of providing written informed consent in person (However, this is not required for patients aged younger than 20 years at the time of consent or patients with intellectual disability associated with MPS II whose willingness cannot be verified.)
3. For patients aged younger than 20 years at the time of consent or patients with intellectual disability associated with MPS II whose willingness cannot be verified, written consent must be obtained from the legally acceptable representative. (Wherever possible, written consent of the patient should be obtained.)
4. Male patient whose partner is of child-bearing potential and agrees to use a medically accepted, highly effective method of contraception.

Exclusion Criteria:

1. A patient who used any concomitant medication or therapy that could affect study assessments in the opinion of the investigator or subinvestigator.
2. A patient with a history of serious drug allergy or hypersensitivity that precludes participation in this study in the opinion of the investigator or subinvestigator.
3. A patient judged to be ineligible by the investigator or subinvestigator for other reasons.