De novo loss of function variants in the SYNGAP1 gene cause an autosomal dominant neurodevelopmental condition (Hamdan et al., 2009), which is currently named SYNGAP1-related Developmental and Epileptic Encephalopathy (SYNGAP1-DEE, orphanet code: 544254). This evidence concerns the gene SYNGAP1 and developmental and epileptic encephalopathy.