Rett syndrome is a disorder of brain development that occurs almost exclusively in girls. After 6 to 18 months of apparently normal development, girls with the classic form of Rett syndrome develop severe problems with language and communication, learning, coordination, and other brain functions. Early in childhood, affected girls lose purposeful use of their hands and begin making repeated hand wringing, washing, or clapping motions. They tend to grow more slowly than other children and have a small head size (microcephaly). Other signs and symptoms can include breathing abnormalities, seizures, an abnormal curvature of the spine (scoliosis), and sleep disturbances.

Researchers have described several variants of Rett syndrome with overlapping signs and symptoms. The atypical forms of this disorder range from a mild type, in which speech is preserved, to a very severe type that has no period of normal development. A form of Rett syndrome called the early-onset seizure variant has most of the characteristic features of classic Rett syndrome, but also causes seizures that begin in infancy.

source: ghr.nlm.nih.gov