SYNGAP1 and Pelizeaus-Merzbacher spectrum disorder: We administered the validated Social Responsiveness Scale, Second Edition (SRS-2) to investigate the phenotypic presentation of social-behavioral impairments for the developmental synaptopathy—SYNGAP1-related Intellectual Disability (SYNGAP1-ID) (n = 32) compared with a phenotypically similar disorder Phelan-McDermid syndrome (PMD) (n = 27) and healthy controls (n = 43).