There is no known single cause
for autism, but it is generally accepted that it is caused by abnormalities
in brain structure or function. Brain scans show differences in the shape
and structure of the brain in autistic versus non-autistic children.
Researchers are investigating a number of theories, including the link
between heredity, genetics and medical problems. In many families, there
appears to be a pattern of autism or related disabilities, further
supporting a genetic basis to the disorder. While no one gene has been
identified as causing autism, researchers are searching for irregular
segments of genetic code that autistic children may have inherited. It also
appears that some children are born with a susceptibility to autism, but
researchers have not yet identified a single "trigger" that causes autism to
develop.
Other researchers are
investigating the possibility that under certain conditions, a cluster of
unstable genes may interfere with brain development resulting in autism.
Still other researchers are investigating problems during pregnancy or
delivery as well as environmental factors such as viral infections,
metabolic imbalances, and exposure to environmental chemicals.