Safety and Clinical Outcomes in Hunter Syndrome Patients 5 Years of Age and Younger Receiving Idursulfase Therapy

This study will provide a basis for evaluating the safety of idursulfase administered to Hunter syndrome patients who are ≤ 5 years old. Additionally, this study will provide a basis for evaluating the idursulfase single- and repeated-dose pharmacokinetic profiles as well as the pharmacodynamic effect (as measured by urinary GAG excretion) in this pediatric population. Additional exploratory measures will include abdominal ultrasound measurements of liver and spleen volumes, assessments of growth with comparisons to normal population growth data, assessments of annualized growth velocity, assessments of routine developmental milestones using the Denver II, and assessments of clinical events, including the first occurrence of certain hearing-related events (e.g., hearing loss, otitis media), respiratory-related events (e.g., upper and lower respiratory infections), and specific surgical procedures (e.g., adenoidectomy, placement of PE tubes).

All patients in this open-label study will receive once-weekly infusions of idursulfase at a dose of 0.5 mg/kg.

Inclusion criteria

• The patient has a diagnosis of Hunter syndrome based upon biochemical criteria either documented in their medical history or established at Screening:

• A deficiency in iduronate-2-sulfatase (I2S) enzyme activity of ≤ 10 % of the lower limit of the normal range as measured in plasma, fibroblasts, or leukocytes (based on normal range of measuring laboratory)

AND

• A normal enzyme activity level of one other sulfatase as measured in plasma, fibroblasts, or leukocytes (based on normal range of measuring laboratory).
• The patient is 5 years of age and under.
• The patient is male.
• The patient's parent(s), or patient's legal guardian must have voluntarily signed an Institutional Review Board approved informed consent form after all relevant aspects of the study have been explained and discussed with the patient's parent(s), or the patient's legal guardian.

Exclusion criteria

• The patient has received treatment with another investigational therapy within 30 days prior to enrollment.
• The patient has clinically relevant medical condition(s) making implementation of the protocol difficult.
• The patient has previously received idursulfase.
• The patient has known hypersensitivity to any of the components of idursulfase.
• The patient has had a tracheostomy.