Mapping the Genotype, Phenotype, and Natural History of Phelan-McDermid Syndrome

Inclusion Criteria: * Individuals older than 18 months of age with pathogenic deletions or mutations of the SHANK3 gene * English speaking individuals Exclusion Criteria: * Has taken an investigational drug as part of another research study, within 30 days prior to study enrollment * For subjects involved in imaging biomarker assessment: contraindications to 3T MRI scanning, such as metal implants/non-compatible medical devices or medical conditions, including vagus nerve stimulator * For subjects involved in EEG/ ERP biomarker assessment: contraindications to EEG/ERP, such as uncooperative or destructive behaviors preventing lead placement or capture by ERP/VEP equipment. Under age 2 or over age 11 at the time of enrollment. * Unwilling or unable to comply with study procedures and assessments