SLC6A1 and language disorder: Indeed, in the case of SLC6A1, the initial core phenotype was that of myoclonic-atonic epilepsy associated with language disorders and various degrees of ID (Carvill et al., 2015; Johannesen et al., 2018), while variability in phenotypic expression in SLC6A1 families has been poorly explored, and very few familial cases have been reported, usually included in larger cohorts (Carvill et al., 2015; Johannesen et al., 2018; Goodspeed et al., 2020).