How did my child develop autism?

No one knows for sure. Though it's understandable to expect that a disorder as common as autism would have a known cause, in many ways it's still quite mysterious. Recent studies suggest a strong genetic basis for autism -- up to 20 sets of genes may play a part in its development. Genetics alone, however, can't account for all the cases, and so scientists are also looking into possible environmental origins, as well as other triggers.