Rett syndrome is classified under the Pervasive Developmental Disorders, but Rett syndrome has identifiable physical differences such as reduced muscle tone (causing the child to seem "floppy") and stereotyped hand movements such as wringing and waving.
Additionally, Rett syndrome produces an identifiable chromosomal difference.
- Rett syndrome is a neurodevelopmental disorder that causes severe disability in young children, mostly girls. After a period of relatively normal development, children with Rett syndrome lose skills such as language, play and hand use. The hallmark of the disorder is the development of midline hand wringing or patting movements that may be constant while the child is awake. Head growth, which is a reflection of brain growth, slows down in the 1st and 2nd years of life. Rett syndrome is caused by a mutation (unfavorable change in DNA) in a gene called MECP2 that is on the X chromosome. The mutation itself causes Rett syndrome, as well as other developmental disorders. The diagnosis of Rett syndrome still rests on clinical characteristics. Many girls with Rett syndrome have received a diagnosis of autism during their period of regression, which is why Rett syndrome is currently classified as a "pervasive developmental disorder.