Kleefstra syndrome is an inherited disorder characterized by peculiar facial features, mental retardation, hypotonia, and severe speech delays, inherited in an autosomal dominant manner. Kleefstra syndrome is a rare genetic disorder with a core phenotype that includes mental retardation, developmental delays, speech developmental disorders, hypotonia, and a number of distinctive facial features (e.g., short head, small head, wide forehead, short nose, etc.), in addition to epilepsy, congenital heart disease, genitourinary deficiencies, autistic behavior, and sleep abnormalities. The diagnosis of Kleefstra syndrome is based on genetic testing in addition to typical clinical manifestations. If parents find that their children have the above symptoms, they are advised to go to the hospital in time for a clear diagnosis and targeted treatment.