The purpose of the study is to prospectively assess longitudinal changes in proteolipid protein 1 (PLP1) protein, disease-related biomarkers in cerebral spinal fluid (CSF) and blood, neuroimaging parameters relevant to Pelizaeus-Merzbacher disease (PMD) and longitudinal changes in performance on clinical, participant, and caregiver-reported outcome assessments to inform the development of therapies for PMD.

This is a multi-center, non-randomized, non-interventional integrated prospective and retrospective study in up to 32 participants with PMD who can undergo general anesthesia or conscious sedation (if necessary) to collect fluid biomarkers (CSF and blood), neuroimaging, and clinical assessments to be used in support of the development of therapies for PMD. The study duration for each participant will be approximately 26 months (Week 106).

Inclusion Criteria:

1. Participant has a parent or caregiver capable of providing informed consent (signed and dated) and able to attend all scheduled study visits and provide feedback regarding the participant's symptoms and performance as described in the protocol and be able to comply with all study requirements
2. Participant has a diagnosis of Pelizaeus-Merzbacher Disease with genetic confirmation of PLP1 duplication
3. Male, 6 months-17 years old, inclusive, at the time of informed consent and phenotype consistent with classic PMD
4. No contraindications for lumbar punctures (LPs), blood draws, neuroimaging, sedation (if necessary) or other study procedures

Exclusion Criteria:

1. Clinically significant abnormalities in medical history or physical examination
2. > 2 copies of the PLP1 gene
3. Have any other conditions, which, in the opinion of the investigator would make the participant unsuitable for inclusion, or could interfere with the participant taking part in or completing the study

Pelizaeus-Merzbacher disease participant population

Ionis may share anonymized individual participant data, aggregated clinical data, and other types of data that support the results in this study. Data requests from qualified researchers will be considered once all three of the following criteria are met: (1) 12 months from marketing approval of the study drug in both the United States and European Union; (2) 18 months from conclusion of the study; and (3) 6 months from publication of study article. Access would be via a secure environment and is contingent upon approval of a research proposal and entry into an appropriate data use agreement. Requests to access data can be submitted via the website https://vivli.org/ourmember/ionis/.