Rett syndrome (RTT) is a rare genetic neurodevelopmental disarray in which children are mostly effected with relapse of previously acquired skills after a period of normal development. Rett syndrome is usually identified in children age between 6to 18 months as they begin to lose the abilities they gained.it is caused by the mutation on the x chromosome on a gene MECP2.There are about 900 different mutations found on MECP2 gene. It is not a degenerative disorder. The course and severity of Rett syndrome is determined by the location, type and severity of the mutation and X-inactivation. In more than 99 percent of people with Rett syndrome, there is no history of the disorder in their family.