Rett syndrome is a disorder of brain development that affects children usually when they are between the ages of six months and a year and a half, the vast majority of them girls.

Children with Rett syndrome start developing normally at first, but then progressively lose the use of their hands and experience repetitive hand movements, problems speaking, mental retardation, abnormalities in walking, and mental retardation.

This fact sheet from the U.S. National Institute of Neurological Disorders and Stroke explains the causes, symptoms, stages of the disease, and more.