A rare genetic developmental and epileptic encephalopathy with characteristics of developmental delay, generalised epilepsy consisting of eyelid myoclonia with absences and myoclonic-atonic seizures, intellectual disability and autism spectrum disorder (ASD). The SYNGAP1 gene (6p21.32) encodes the synaptic Ras-GTPase-activating protein 1, mainly expressed in the synapses of excitatory neurons. Loss of function mutations in SYNGAP1 impairs neuronal homeostasis and development. This disorder is caused by heterozygous pathogenic SYNGAP1 variants or chromosome 6p21.32 microdeletions encompassing the SYNGAP1 gene. The pattern of inheritance is autosomal dominant. [from SNOMEDCT_US]