A syndrome that is characterized by severe mental retardation, hypotonia, brachy(micro)cephaly, epileptic seizures, flat face with hypertelorism, synophrys, anteverted nares, everted lower lip, carp mouth with macroglossia, and heart defects and that has_material_basis_in a microdeletion in the chromosome region 9q34.3 or by a point mutation in the EHMT1 gene located in that region. [ http://purl.obolibrary.org/obo/ECO_0007645 http://purl.obolibrary.org/obo/ECO_0007638 http://purl.obolibrary.org/obo/ECO_0007637 ]