STXBP1 and Epileptic encephalopathy: Hence, apart from being an essential gene, the significance of STXBP1 dysfunction in vivo was not appreciated until its de novo heterozygous mutations were discovered first in epileptic encephalopathies (Saitsu et al., 2008) and later in other neurodevelopmental disorders (Hamdan et al., 2009; Hamdan et al., 2011; Rauch et al., 2012; Deciphering Developmental Disorders Study, 2015).