Ascertainment of PMS participants and collection of clinical phenotypes

Informed consent was obtained from participants’ caregivers for study participation, as described previously.⁸ The cohort included 76 PMS participants (38 females, 38 males) between the ages of 1 and 42 years (8.9 ± 6.5). Forty-six participants were enrolled in studies at the Seaver Autism Center for Research and Treatment at the Icahn School of Medicine at Mount Sinai. An additional 30 participants were enrolled by partner sites through the Rare Disease Clinical Research Network Developmental Synaptopathies Consortium (DSC), as part of a PMS phenotyping and natural history study. For each participant, a comprehensive battery of standardized assessments, semi-structured interviews, and caregiver report questionnaires was used to examine medical comorbidities, intellectual and adaptive functioning, expressive and receptive language, ASD symptomatology, and behavioral comorbidities, as described previously.⁸ Studies were approved by the Institutional Review Board (IRB) for the protection of human subjects at Mount Sinai (study IDs: 98-0436, 10-0527, 12-1718) and Boston Children’s Hospital (study ID: P00013300), which serves as the central IRB for the DSC.