The primary purpose of this study is to evaluate the safety and tolerability of ION356.
Participant's parent or legally accepted representative can provide informed consent, attend all scheduled study visits, provide feedback regarding the participant's symptoms, and can comply with all study requirements.
Diagnosis of PMD with genetic confirmation of PLP1 gene duplication.
Clinical phenotype and brain imaging consistent with a diagnosis of PMD.
Male between the ages of 2 and 17 years, inclusive, at the time of informed consent.
Clinically significant abnormalities in medical history, laboratory tests or physical examination.
Unwillingness to comply with study procedures, including follow-up, as specified by this protocol, or unwillingness to cooperate fully with the Investigator.
Any contraindication or unwillingness to undergo magnetic resonance imaging (MRI).
Treatment with another investigational drug, biological agent, or device within 1 month of Screening, or 5 half-lives of the investigational agent, whichever is longer.