Rett synrome/ disorder is a neurodevelopmental disorder that is classified as a pervasive developmental disorder by the DSM-IV. Many argue that this is a misclassification just as it would be to include such disorders as fragile X syndrome, tuberous sclerosis, or Down syndrome where one can see autistic features. The symptoms of this disorder are most easily confused with those of Angelman syndrome and autism. The clinical features include a deceleration of the rate of head growth (including microcephaly in some) and small hands and feet. Stereotypic, repetitive hand movements such as mouthing or wringing are also noted. Symptoms of the disorder include cognitive impairment and problems with socialization, the latter during the regression period. Socialization typically improves by the time they enter school. Girls with Rett syndrome are very prone to gastrointestinal disorders and up to 80% have seizures. They typically have no verbal skills, and about 50% of females are not ambulatory. Scoliosis, growth failure, and constipation are very common and can be problematic.