Like all syndromes, autism is assumed to be composed of many subtypes, each with different etiologies and possible treatments. Anything that can cause damage to the parts of the brain that produce these symptoms is called autism. Autism is a spectrum disorder . In the triad of symptoms, there are many possible combinations. 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.