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ASD is a clinical diagnosis; there are no lab tests to establish or rule out ASD (although there are tests to identify various underlying causes of ASD).
ASD is a "syndrome" (from the Greek words meaning "run together" - the way a group of horses might run together). ASD affects four areas of functioning: social relatedness, language, cognitive flexibility, and sensorimotor processing. Symptoms in each of these domains can range from totally disabling to extremely subtle. Sometimes, features in one or two areas may be so mild as to escape detection, until the diagnosis is made.
The symptoms of ASD usually improve over time, even without treatment. The higher a child's level of intelligence, the faster and more completely the symptoms improve (more on this in a later post).
A typical sequence of events might look like this:
• Social: No eye contact > intermittent eye contact > good eye contact but difficulty with knowing how to initiate or sustain a social interaction
• Language: Nonverbal, may act deaf > speech limited to echolalia (repetition) and delayed echolalia ("scripting") > speaks well, but has a hard time with verbal nuance (fibbing, verbal humor, tone of voice, conversational turn-taking)
• Cognitive Rigidity: Intense distress with transitions or changes in routine, and frequent, intense flapping and toe-walking > preoccupation with specific topics (the alphabet, computer games, mechanical objects), and occasional reappearance of flapping and toe-walking when excited
• Sensorimotor processing: Extreme food selectivity; "acts deaf," craves deep pressure > gradual lessening of intensity although traits may persist
If you haven't already done so, I recommend that you read Leo Kanner's original (1943) paper on autism (http://www.neurodiversity.com/library_kanner_1943.pdf ). In that paper, Kanner describes all of the features we recognize today as autism. He also describes this evolution of symptoms:
"Between the ages of 5 and 6 years, they gradually abandon the echolalia...Noises and motions are tolerated more than previously...The repetitiousness assumes the form of obsessive preoccupations. .. the children begin to play in a group, still never with the other members of the play group, but at least on the periphery alongside the group [emphasis in the original]...All of this makes the family feel that, in spite of recognized ‘difference' from other children, there is progress and improvement." [Kanner, 1943]
In 1971, Kanner published a follow-up paper on his original eleven patients. Several had skilled jobs, and one had obtained a college degree.
For additional details on the "natural history" of ASD, see Chapter 1 in my book, Making Sense of Autistic Spectrum Disorders; Bantam-Dell 2010; http://www.randomhouse.com/catalog/display.pperl?isbn=9780553806816 )
All of this is nice, but it makes it harder to separate claimed treatment effects from the naturally-occurring improvement in a child's condition. This, of course, is a big sticking point when it comes to evaluating the claimed efficacy of various "treatments" for ASD, many of which are simply capitalizing on naturally-occurring improvement that would have occurred anyway. More in this in another post.
