Participants
Individuals, or the parents or guardians of individuals, who have aPLP1 -related disorder and an identified PLP1 pathogenic variant, were invited to participate in the study. Participants were identified through one of three mechanisms. 1) Those who had previously participated in a PLP1 -related disorders (PLP1-RD) study at Wayne State University/Detroit Medical Center (WSU/DMC) or who were participating in a different PLP1 study at the time of enrollment; 2) Those who had been seen/were being seen at WSU/DMC for clinical care or who had contacted the primary investigator because of a diagnosis of PLP1-RD ; 3) Those who had genetic testing forPLP1-RD through the molecular genetics laboratory at AI Dupont in Wilmington, DE. Recruitment was conducted either through mail or in person (for those who were being seen at WSU/DMC or Dupont during the period of enrollment). Potential participants/parents/guardians were sent or given a study packet that included the consent form with HIPAA authorization, an assent form (when applicable), a medical history questionnaire, a family history questionnaire, medical record release forms, and a “decline to participate” form. Individuals who had already filled out the questionnaires as part of ongoing/previousPLP1 -related disorders studies or clinical care instead received a follow-up “current medical history” questionnaire. For all potential participants, those who did not return the “decline to participate” form within two weeks were contacted by telephone by a study investigator to answer questions about the study. Participants were also asked to consider taking part in an optional long-term follow up which involves completing a one-page ”current medical history” questionnaire every 1-2 years.