MLL2 (MIM 602113; NM_003482, chromosome 12q13.12), a gene encoding a histone 3 lysine 4 (H3K4) methyltransferase of the trithorax group, has recently become of high interest for clinical and molecular genetics since the identification of de novo dominant MLL2 mutations as the major cause of Kabuki syndrome 1. The gene discussed is KMT2B; the disease is Kabuki syndrome.