Females with the disorder are more likely, however, to exhibit more severe mental retardation. By definition, the onset of Autistic Disorder is prior to age 3 years. In some instances, parents will report that they have been worried about the child since birth or shortly afterward because of the child's lack of interest in social interaction. Manifestations of the disorder in infancy are more subtle and difficult to define than those seen after age 2 years. Autistic Disorder follows a continuous course.
Some individuals deteriorate behaviorally during adolescence, whereas others improve.
Available follow-up studies suggest that only a small percentage of individuals with the disorder go on as adults to live and work independently. In about one-third of cases, some degree of partial independence is possible. The highest functioning adults with Autistic Disorder typically continue to exhibit problems in social interaction and communication along with markedly restricted interests and activities. There is an increased risk of Autistic Disorder among siblings of individuals with the disorder. Autistic Disorder must be differentiated from other Pervasive Developmental Disorders.