Rett syndrome is a rare, severely disabling developmental disability that almost exclusively affects females. Children with the disorder often have small hands and feet, experience developmental regression and deceleration in the rate of head growth, and are prone to gastrointestinal disorders, long QT syndrome and seizures. CDKL5 is a similar, rare genetic disorder located on the X chromosome. The disorders sometimes are misdiagnosed as Angelman syndrome, cerebral palsy or autism.