In many families there appears to be a pattern of autism or related disabilities, which suggests there is a genetic basis to the disorder-although at this time no gene has been directly linked to autism. The genetic basis is believed by researchers to be highly complex, probably involving several genes in combination. There are no medical tests for diagnosing autism. An accurate diagnosis must be based on observation of the individual's communication, behavior, and developmental levels. However, because many of the behaviors associated with autism are shared by other disorders, various medical tests may be ordered to rule out or identify other possible causes of the symptoms being exhibited.
Diagnosis is made when a specified number of characteristics are present.
Diagnostic evaluations are based on the presence of specific behaviors indicated by observation and through parent consultation, and should be made by an experienced, highly trained team. Thus, when professionals or parents are referring to different types of autism, often they are distinguishing autism from one of the other pervasive developmental disorders. Every person with autism is an individual, and like all individuals, has a unique personality and combination of characteristics. There are great differences among people with autism. Some individuals mildly affected may exhibit only slight delays in language and greater challenges with social interactions.