STXBP1 and developmental and epileptic encephalopathy, 4: Several studies identifying such microdeletions had in fact been focused on patients with diverse seizure phenotypes [1, 12] or aimed at identifying mutations including CNVs involving STXBP1. De novo missense, nonsense, frameshift, and splice-site mutations, as well as genomic deletions of STXBP1, have been found in association with Early Infantile Epileptic Encephalopathy 4 (EIEE4; OMIM #612164) and other epilepsy types [13], such that STXBP1 haploinsufficiency is the accepted cause of these epileptic phenotypes.