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

Open to males ages up to 6 years

• Participant is male.
• Participant is ELAPRASE-naïve at study entry.
• Participant must have a documented diagnosis of MPS II. The following combination will be accepted as diagnostic of MPS II:
  • Participant has a deficiency in iduronate-2-sulfatase (I2S) enzyme activity of less than or equal to (<=) 10 percent (%) of the lower limit of the normal range as measured in plasma, fibroblasts, or leukocytes (based on the reference laboratory's normal range). The participant has a normal enzyme activity level of 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 complex gene rearrangement), which is predicted to lead to development of a persistent anti-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.

• Participant has received treatment with any investigational drug within the 30 days prior 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 marrow transplant at any time.
• Participant has received blood product transfusions within 90 days prior to screening.
• Participant is unable to comply with the protocol as determined by the investigator.
• Participant has known or suspected intolerance or hypersensitivity to the investigational product(s), closely related compounds, or any of the stated ingredients, 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 laboratory assessments.
• Participant has current or relevant history of physical or psychiatric illness, or any medical disorder that may require treatment or make the participant unlikely to fully complete the study, or any condition that presents undue risk from the investigational 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 condition being studied, or could affect the action, absorption, or disposition of the investigational product(s), or clinical or laboratory assessment (Current use is defined as use within 30 days).
• Within 30 days prior to the first dose of investigational product, the participant has been enrolled in a clinical study (including vaccine studies) that, in the investigator's opinion, may impact this study.