SYNGAP1 and Intellectual disability: Mutations that cause heterozygous deletion or dysfunction of the human gene Syngap1 cause a severe form of intellectual disability (synGAP haploinsufficiency, also called Mental Retardation type 5 [MRD5]) often accompanied by autism and/or seizures (Berryer et al., 2013; Hamdan et al., 2011; Hamdan et al., 2009).