**Rocket Study: Understanding Pelizaeus-Merzbacher Disease** Pelizaeus-Merzbacher Disease (PMD) is a rare genetic disorder affecting the brain, caused by changes in a gene called PLP1. This study aims to learn more about PMD by studying changes in certain proteins and other markers in the blood and spinal fluid, as well as through brain scans. By understanding these changes, researchers hope to develop better treatments for PMD. This study will have up to 32 participants and will take about 26 months. Participants will be children aged 6 months to 17 years with confirmed PMD, and they will undergo various tests, which may include sedation if needed, to collect information. **Key Points:** - The study lasts for about 26 months, requiring regular visits to the study center. - Participants will need to have tests like blood draws, spinal fluid collection, and brain scans. - A parent or caregiver must be able to attend all visits and help with the study requirements. Eligible participants must not have more than two copies of the PLP1 gene and should not have any other significant health problems.