A Study of ELAPRASE in Treatment-naïve Participants With Hunter Syndrome (Mucopolysaccharidosis [MPS] II)

Inclusion Criteria:

• Participant is male.

• Participant is ELAPRASE-naïve at study entry.

• Participant must have a documented diagnosis of MPS II. The following combinationwill be accepted as diagnostic of MPS II:

• Participant has a deficiency in iduronate-2-sulfatase (I2S) enzyme activity ofless than or equal to (<=) 10 percent (%) of the lower limit of the normalrange as measured in plasma, fibroblasts, or leukocytes (based on the referencelaboratory's normal range). The participant has a normal enzyme activity levelof at least 1 other sulfatase as measured in plasma, fibroblasts, or leukocytes (based on the reference laboratory's normal range).

• Participant has a documented mutation in the IDS gene; additionally,participants must have a severe mutation (example, large deletion or complexgene rearrangement), which is predicted to lead to development of a persistentanti-idursulfase antibody response.

• Participant will be less than (<) 6 years of age at enrollment.

• Participant has a negative test result for serum anti-idursulfase antibodies.

Exclusion Criteria:

• Participant has received treatment with any investigational drug within the 30 daysprior to study entry.

• Participant has received or is receiving treatment with idursulfase-IT.

• Participant has received growth hormones, a cord blood infusion, or a bone marrowtransplant at any time.

• Participant has received blood product transfusions within 90 days prior toscreening.

• Participant is unable to comply with the protocol as determined by the investigator.

• Participant has known or suspected intolerance or hypersensitivity to theinvestigational product(s), closely related compounds, or any of the statedingredients, including the prophylactic ITR.

• Participant has current or recurrent disease that could affect the action,absorption, or disposition of the investigational product, or clinical or laboratoryassessments.

• Participant has current or relevant history of physical or psychiatric illness, orany medical disorder that may require treatment or make the participant unlikely tofully complete the study, or any condition that presents undue risk from theinvestigational product or procedures.

• Participant has current use of any medication (including over-the-counter, herbal,or homeopathic preparations) that could affect (improve or worsen) the conditionbeing studied, or could affect the action, absorption, or disposition of theinvestigational product(s), or clinical or laboratory assessment (Current use isdefined as use within 30 days).

• Within 30 days prior to the first dose of investigational product, the participanthas been enrolled in a clinical study (including vaccine studies) that, in theinvestigator's opinion, may impact this study.