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.
Autism tends to occur more frequently than
expected among individuals who have certain medical conditions,
including Fragile X syndrome, tuberous sclerosis, congenital
rubella syndrome, and untreated phenylketonuria (PKU).
Some harmful substances ingested during pregnancy also
have been associated with an increased risk of autism.
Early in 2002, The Agency for Toxic Substances and Disease
Registry (ATSDR) prepared a literature review of hazardous
chemical exposures and autism and found no compelling
evidence for an association; however, there was very limited
research and more needs to be done.
The question of a relationship between vaccines
and autism continues to be debated. In a 2001 investigation
by the Institute of Medicine, a committee concluded that
the "evidence favors rejection of a causal relationship....
between MMR vaccines and autistic spectrum disorders (ASD)."
The committee acknowledged, however, that "they could
not rule out" the possibility that the MMR vaccine
could contribute to ASD in a small number of children.
While other researchers agree the data does not support
a link between the MMR and autism, more research is clearly
needed.
Whatever the cause, it is clear that children
with autism and PDD are born with the disorder or born
with the potential to develop it. It is not caused by
bad parenting. Autism is not a mental illness. Children
with autism are not unruly kids who choose not to behave.
Furthermore, no known psychological factors in the development
of the child have been shown to cause autism.
