Scientists don't know exactly what causes autism at this time. Much evidence supports the idea that genetic factors—that is, genes, their function, and their interactions—are one of the main underlying causes of ASDs. But, researchers aren't looking for just one gene. Current evidence suggests that as many as 12 or more genes on different chromosomes may be involved in autism, to different degrees.
Some genes may place a person at greater risk for autism, called susceptibility. Other genes may cause specific symptoms or determine how severe those symptoms are. Or, genes with changes or mutations might add to the symptoms of autism because the genes or gene products aren't working properly.
Research has also shown that environmental factors, such as viruses, may also play a role in causing autism.
While some researchers are examining genes and environmental factors, other researchers are looking at possible neurological, infectious, metabolic, and immunologic factors that may be involved in autism.
