An Observational Study Evaluating Anti-Idursulfase Serum Antibody Response in Hunter Syndrome Patients

This study is being conducted to satisfy post-marketing commitments to monitor
anti-idursulfase antibody development in Hunter syndrome patients after long-term idursulfase
enzyme replacement therapy. The study will be conducted as a sub-study within the Hunter
Outcome Survey (HOS). Hunter syndrome patients in the HOS who have previously received
idursulfase as well as treatment-naive patients who will begin idursulfase treatment within
30 days of study enrollment will be included.

Inclusion Criteria:

Patients must meet all of the following criteria to be considered eligible for enrollment:

- The patient is male and enrolled in the HOS (i.e., meets the entry criteria of a
documented diagnosis of Hunter syndrome)

- The patient is ≥ 5 years-old

- The patient is on idursulfase treatment or scheduled to begin idursulfase treatment
within 30 days of study enrollment

- The patient, patient's parent(s), or patient's legally authorized guardian must have
voluntarily signed an Institutional Review Board (IRB)/Independent Ethics Committee
(IEC)-approved informed consent form after all relevant aspects of the study have been
explained and discussed with the patient, patient's parent(s), or patient's legally
authorized guardian.

Exclusion Criteria:

Patients who meet any of the following criteria are not eligible for this study:

- The patient has received biologic/ERT products other than idursulfase, or other
investigational product(s) for any reason within 30 days prior to study entry.

- The patient has a life expectancy of < 2 years

- The patient is unable to comply with the protocol, e.g., has a clinically relevant
medical condition making implementation of the protocol difficult; has an
uncooperative attitude; is unable to return for safety evaluations; or is otherwise
unlikely to complete the study, as determined by the Investigator.