SCN8A and Epileptic encephalopathy: In addition, a substantial number of genes are epileptic encephalopathy genes (STXBP1, SCN1A, SCN2A, SCN8A, GRIN2A, GRIN2B, HCN1, SLC6A1, KCNA2, EEF1A2, KCNB1 and SYNGAP1) and are related with mental retardation and epilepsy (IQSEC2 and MEF2C).