Eight of those (SCN1A, IQSEC2, STXBP1, CACNA1E, ARID1B, DDX3X, WHSC1, PHF21A) have been known to be responsible for NDDs associated with IDs or epilepsies.9, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29. This evidence concerns the gene PHF21A and epilepsy.