Mutations in KMT2D (MIM 147920), NF1 (MIM 162200), and ZEB2 (MIM 235730) are known to cause human monogenic Mendelian syndromes (Kabuki syndrome, neurofibromatosis type 1, and Mowat-Wilson syndrome, respectively), and cardiac malformations in these syndromes occur in 3–50% of patients. Here, KMT2D is linked to Mowat-Wilson syndrome.