Rett syndrome is diagnosed through a clinical examination that looks for specific signs and behaviours; it is confirmed through genetic testing. It can occur, however, without any of the currently known genetic mutations. As with any medical condition there is a large amount of variation in people with Rett syndrome. For example some girls learn to walk, although in an abnormal way, while others are never able to walk independently. There are two types of diagnoses to be made: typical or classic RTT and atypical or variant RTT.
Typical or classic RTT is characterized by a period of regression followed by recovery or stabilization. It requires the presence of 4 main criteria – partial or complete loss of acquired purposeful hand skills, partial or complete loss of acquired spoken language, gait abnormalities and stereotypical hand movements, and must meet 2 exclusion criteria – no brain injury secondary to trauma and no grossly abnormal psychomotor development in the first six months of life. Some other supportive criteria are often present in this type of RTT but they are not required for the diagnosis.