Sponsor decision

This is an observational study planned to document prospectively disease manifestation and neurocognitive course in pediatric patients with a clinical presentation consistent with neuronopathic ("severe") MPS II undergoing current standard of care and/or intrathecal Elaprase® for their condition. Some patients may be offered the opportunity to screen for a gene therapy study conducted by the same sponsor.

MPS II is a rare X-linked recessive genetic disease caused by mutations in the iduronate-2-sulfatase gene (IDS). Enzyme replacement therapy (ERT) with recombinant idursulfase (ELAPRASE®) is the only approved product for the treatment of Hunter syndrome; however, ERT as currently administered does not cross the blood brain barrier and is therefore unable to address the unmet need in MPS II patients with CNS (neurocognition and behavior) involvement. This is an observational study to document prospectively disease manifestation and neurocognitive course in pediatric patients with a clinical presentation consistent with neuronopathic ("severe") MPS II undergoing current standard of care for their condition. Approximately forty pediatric subjects who have severe MPS II will be enrolled. Changes in neurodevelopmental parameters of cognitive, behavioral, and adaptive function over time will be the primary focus for a duration of 104 weeks.

Inclusion Criteria:

1. Meets any of the following criteria:

   1. Has a clinical diagnosis of severe MPS II and has a documented mutation in IDS, OR
   2. Has a relative clinically diagnosed with severe MPS II who has the same IDS mutation as the subject, OR
   3. Has documented mutation(s) in IDS that in the opinion of the investigator is known to result in a neuronopathic phenotype

2. Has sufficient communication capacity to complete the required protocol testing

Patient's legal guardian must be willing and able to provide written, signed informed consent.

Exclusion Criteria:

1. Has had prior treatment with an AAV-based gene therapy product
2. Is currently participating in a clinical trial of an investigational product for the treatment of MPS II with the exception of IT ELAPRASE trials; no investigational product may be taken starting 30 days or 5 half-lives of the investigational product prior to signing the ICF, whichever is longer

Up to 40 subjects ages 1 month to 8 years of age who have documented neurocognitive deficits due to MPS II or who have a genotype and family history consistent with an inherited form of severe MPS II will be invited to participate.