Remarkably, genetic variants in the histone methyltransferase KMT2D were associated with Kabuki syndrome type 1, characterized by typical facial features, postnatal growth deficiency, organ malformations and NDD, whereas pathogenic variants in KMT2C were associated with Kleefstra syndrome (OMIM # 617768), an autosomal dominant chromatinopathy characterized by delayed psychomotor development, variable intellectual disability and mild dysmorphic features such as microcephaly, flattened midface and prominent eyebrows [55,56,57]. This evidence concerns the gene KMT2D and microcephaly.