STXBP1 and epilepsy: We were able to determine the definitive causes in 8 families because the pathogenic or causal variants were identified in known epilepsy genes including SCN1A, CDKL5, STXBP1, CHD2, SCN3A, SCN9A, TSC2, MBD5, POLG and EFHC1. Mutations in these genes have been commonly identified in Caucasian children with epilepsy disorders.