Autism clearly has a genetic component, since if one half of a set of identical twins suffers from the disorder, the other generally does as well. But there are also a high number of cases where it seems to appear spontaneously, with affected children being born in families with no history of problems.
In recent years, new molecular tools like DNA chips have allowed researchers to look at these sporadic cases in more detail. The results have suggested that spontaneous mutations may play a large role in causing the disease. But these studies were limited to looking at large changes, the loss or duplication of huge regions of the genome. Technology has marched on, however, and DNA sequencing has reached the point where we're now able to look for small individual changes in the genomes of families with an autistic member. These new studies reinforce the role of spontaneous mutations, but suggest that up to a thousand genes may be behind autistic behavior.
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