This research study is evaluating an investigational drug for children with Hunter syndrome. Your child may be able to take part in this study if they:

• Have a confirmed diagnosis of Hunter syndrome (MPS II) 
• Are between 30 and 71 months of age (2.5 years old to younger than 6 years old) and meet certain cognitive/developmental requirements OR are 6 years of age or older with an IQ of 70 or higher
• Are able to undergo lumbar punctures (medical procedures to collect samples of cerebrospinal fluid)
• Have not received hematopoietic stem cell transplantation (HSCT) with successful engraftment
• Have not received gene therapy treatment in a study

Additional criteria may apply.

Study participants will be assigned to 1 of 2 groups – Group A or Group B – for a study duration of 12 or 24 months. Approximately 80 participants will be enrolled, and they will be reimbursed for travel and certain study-related expenses.

Study participants who qualify and meet all eligibility criteria will receive either the investigational drug or the standard-of-care treatment, which is enzyme replacement therapy (known commercially as Elaprase®), through weekly IV infusions (through a vein). The probability of receiving the investigational drug or the standard-of-care treatment is 50/50. This is an open-label study, and both the researchers and participants will know which study treatment is being administered. Participants will also undergo a variety of tests and procedures during the study, such as blood and image tests, cognitive testing and lumbar punctures.

Study participants assigned to the standard-of-care group may be eligible to switch to the investigational drug during the study if certain clinical criteria are met. Participants may also be eligible to join a long-term extension study, which provides an opportunity for participants to receive the investigational drug for a longer period.

If eligible, participation will last between 12 and 24 months. The total study duration will depend on the group to which a participant is assigned. After participation is complete in this study, there may be an option for a 4-to-5-year extension study.

The investigational drug is a genetically engineered molecule that contains the IDS enzyme that is absent in people with Hunter syndrome. This enzyme attaches to another molecule that permits it to penetrate the brain.

The investigational drug replaces the IDS enzyme to treat both forms of Hunter syndrome – the neuropathic form, which affects the central nervous system and brain function, and the systemic form, which affects only the body.

This study aims to evaluate the efficacy and safety of the investigational drug, which is delivered by IV infusion (through a vein), compared to the standard-of-care treatment.

Do not discontinue giving your child any current medications or treatments unless you are advised to do so by the study centre staff or their primary care provider.

There is no cost to you for your child’s participation in the study.