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.

Medical Components of ASD

Gastrointestinal System

Autism may cause alterations in the beneficial bacteria that inhabit the digestive tract, leading to digestive disorders such as diarrhea and constipation. Some symptoms are worsened by certain foods, such as milk or wheat products (see Autism Spectrum Disorders and the Immune System by Paula Goines, B.S., Paul Ashwood, Ph.D., and Judy Van de Water, Ph.D.).

Immune System

Research suggests that problems with the immune system may be one of the causes or consequences of ASD. Psychological stressors, exposure to chemical triggers and infectious agents may work together to adversely influence the immune system. Children at risk of ASD may be particularly susceptible to chemical/environmental triggers of improper immune responses that impact the developing nervous system (see Can Exposure to Environmental Toxicants Influence Autism Susceptibility? by Isaac N. Pessah, Ph.D.).

Elevated Toxins

Findings indicate that many children with autism or those who are at risk of developing autism have a metabolic impairment that reduces their ability to rid their bodies of heavy metals and other toxins. Build-up of these toxins in the body can lead to brain and nervous system damage and developmental delays. These include methylmercury, arsenic, lead and cadmium, which enter human bodies through air, food and water, and over time can cause a range of illnesses and organ damage, including cancer; damage to the kidneys, GI tract and nervous system; and even death. These toxins are particularly dangerous to infants, fetuses and children (see We’re Loaded with Toxins: Analyzing the Toxic Body Burden of Americans by Judy Chinitz Gorman).

Last updated: 29 January 2008