Prevalence
Data are limited to mostly case series, and it appears that Rett's Disorder is much less common than Autistic Disorder. This disorder has been reported only in females.
Course
The pattern of development regression is highly distinctive. Rett's Disorder has its onset prior to age 4 years, usually in the first or second year of life. The duration of the disorder is lifelong, and the loss of skills is generally persistent and progressive. In most instances, recovery is quite limited, although some very modest developmental gains may be made and interest in social interaction may be observed as individuals enter later childhood or adolescence. The communicative and behavioral difficulties usually remain relatively constant throughout life.
Differential Diagnosis
Periods of developmental regression may be observed in normal development, but these are neither as severe nor as prolonged as in Rett's Disorder. For the differential between Rett's Disorder and Autistic Disorder, see Autistic Disorder. Rett's Disorder differs from Childhood Disintegrative Disorder and Asperger's Disorder in its characteristic sex ration, onset, and pattern of deficits. Rett's Disorder has been diagnosed only in females, whereas Childhood Disintegrative Disorder and Asperger's Disorder appear to be more common in males. The onset of symptoms in Rett's Disorder can begin as early as age 5 months, whereas in Childhood Disintegrative Disorder the period of normal development is typically more prolonged (i.e., at least until age 2 years). In Rett's Disorder, there is a characteristic pattern of head growth deceleration, loss of previously acquired purposeful hand skills, and the appearance of poorly coordinated gait or trunk movements. In contrast to Asperger's Disorder, Rett's Disorder is characterized by a severe impairment in expressive and receptive language development.
(299.80 Rett's Disorder from the Diagnostic and Statistical Manual of Mental Disorders: DSM IV)
