A syndrome that is characterized by developmental delay, intellectual disability, muscle weakness (hypotonia), epilepsy, distinctive facial features and congenital malformations of the heart, urogenital tract and the central nervous system, and has_material_basis_in either a chromosome 17 (17q21.31) microdeletion or a mutation in the KANSL1-gene. [ http://purl.obolibrary.org/obo/ECO_0007636 http://purl.obolibrary.org/obo/ECO_0007637 http://purl.obolibrary.org/obo/ECO_0007646 http://purl.obolibrary.org/obo/ECO_0007638 http://purl.obolibrary.org/obo/ECO_0007645 ]