Rett syndrome (RTT) is a genetically-encoded neurodevelopmental disorder that occurs almost exclusively in females and arises from deficiencies in the function of the methyl-CpG binding protein 2 gene (MeCP2). Rett syndrome (RTT) was first described by Austrian paediatrician Andreas Rett in 1966. RTT is characterized by arrested development at about 1 year of age, regression of acquired skills and mental retardation. The clinical features include small hands and feet and a deceleration of the rate of head growth. Repetitive stereotyped hand movements, such as wringing, are also noted. Females with Rett syndrome are prone to gastrointestinal disorders and up to 80% have seizures. They typically have no verbal skills, and many individuals affected do not walk. Scoliosis, growth failure, and constipation are common and can be problematic. Along with the core symptoms of RTT, disturbances in breathing are particularly troublesome (see below). RTT is severely debilitating and patients require constant and life-long care from family members and medical institutions.