Koolen Syndrome (17q21.31 microdeletion syndrome) results when a small piece of chromosome 17 is missing.
People with Koolen Syndrome (17q21.31 microdeletion syndrome) have developmental delay and intellectual disability. Typically their disposition is described as cheerful, sociable, and cooperative. They usually have weak muscle tone (hypotonia) in childhood. About half have recurrent seizures (epilepsy), they may also have vision problems. Males with 17q21.31 microdeletion syndrome often have undescended testes (cryptorchidism). Defects in the walls between the chambers of the heart (septal defects) or other cardiac abnormalities, kidney problems, and skeletal anomalies such as foot deformities occur in some affected individuals.