Utilizing a structured sleep assessment tool, the Childhood Sleep Habits Questionnaire (CSHQ), we discovered that children with two neurodevelopmental disorders due to mutations in synaptic protein encoding genes, Phelan-McDermid syndrome (PMD) and SYNGAP1-related Intellectual Disability (SYNGAP1-ID) have significant sleep disturbances. This evidence concerns the gene SYNGAP1 and Pelizeaus-Merzbacher spectrum disorder.