SCN3A and epilepsy: Recently, de novo heterozygous pathogenic variants of SCN3A/NaV1.3 have been identified in an early infantile DEE (Figure 3) characterized by multifocal seizures, severe intellectual disability and, for some cases, polymicrogyria (multiple small gyri creating excessive folding of the cerebral cortex) (Zaman et al., 2018), as well as in families showing speech and oral motor dysfunctions associated with polymicrogyria of the perisylvian cerebral cortex but that did not typically show epilepsy (Smith et al., 2018).