The causative genes identified in this study encompassed 28 causative genes, of which 15 were primary epilepsy genes (CACNA1A, KCNC1, KCNH5, KCNQ2, NRXN1, PRRT2, SCN1A, SCN2A, SCN8A, SLC2A1, STXBP1, SYNGAP1, TSC1, TSC2, WWOX) and 13 were syndromic epilepsy genes or syndromes (Phelan–McDermid Syndrome/22q13.33 deletion syndrome—ARSA, ALG12; chromosome 16p12.2p11.2 deletion syndrome—CLN3, EIF2B5, MECP2, MT-CYB, NEXMIF/KIAA2022, NFIA, NR2F1, P4HTM, PPP2R5D, PTCD3, PURA, RAI1, UBE3A). The gene discussed is PPP2R5D; the disease is Down syndrome.