SYNGAP1 and epilepsy: In large-scale studies, almost all SYNGAP1 variants associated with NSID, ASD, and epilepsy are loss-of-function and lead to SYNGAP1 haploinsufficiency, resulting in intellectual developmental disorder (Hamdan et al., 2011; Berryer et al., 2013; Carvill et al., 2013; Fieremans et al., 2016).In our study, as well as previous observations, suggest that the SYNGAP1 c.664-2A>G variant would cause ID mainly through a mechanism of haploinsufficiency.