For example, you can have a very high IQ and be severely socially impaired. Autism is a developmental diagnosis. Expression of the symptoms varies with both the chronological age, mental age and developmental level of the person. Symptoms may fluctuate, abate, change and even disappear, but once autistic, that person is always autistic. Autistic persons have a normal life expectancy, and the majority require lifelong social support systems due to their developmental handicaps and continuing symptomatology.
Autism is a retrospective diagnosis.
While symptoms can appear as early as the first months of life, some children will display normal development until 12 to 24 months of age. Since most children are not evaluated by a physician until they are older, it is not possible to make a differential diagnosis until a careful developmental history is obtained. Autism is ubiquitous. It occurs in all parts of the world, in all races and colors, and in all types of families. No social or psychological characteristics of parents or families have proven to be associated with autism.