The etiology of autism is unknown; data suggest that autism results from multiple etiologies with both genetic and environmental contributions. One proposed etiology for autism is viral infection very early in development. The mechanism, by which viral infection may lead to autism, be it through direct infection of the central nervous system, through infection elsewhere in the body acting as a trigger for disease in the central nervous system, through alteration of the immune response of the mother or offspring, or through a combination of these, is not yet known.