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Causes of autism

When a loved one is diagnosed with autism spectrum disorder, it is natural to ask why. Unfortunately, we still don’t know all the answers.

Autism is a diagnosis based on the observation of particular behaviours; currently, we have no reliable biological test for autism. Eventually, we may discover that autism is not a single disorder but a group of disorders with many different causes, which would help explain how it varies so much in symptoms and severity.

For now, we don’t know the exact cause of autism however research suggests it’s a combination of developmental, genetic and environmental factors. What we do know quite clearly is what does not cause autism.

What causes autism?

Autism is strongly genetic

  • Families with one child with autism have an increased risk of having another child with autism when compared with the general population. The risk of having another affected child is estimated to be around 1 in 5.
  • Family members of a person with autism also tend to have higher rates of autistic traits.
  • Twin studies demonstrate that when one identical (monozygotic) twin is affected by autism, there’s a very high chance the other twin will be affected too (77% in one large study). With fraternal (dizygotic) twins, who have a different genetic makeup to each other, the risk is much less.

Google ‘autism and genes’ and you’ll find it’s a thriving area of autism research. Unfortunately, about the only thing that’s clear at the moment is that the genetics of autism are extremely complex, with hundreds of different possible ‘risk genes’ and pathways identified, some involving multiple genes in combination with environmental factors.

Older parents may be a factor

There is growing evidence that older fathers and mothers (over 45 years) are at increased risk of having a child with autism. Older parents, as a rule, are more likely to have children with developmental and other disorders. While the cause is most likely genetic, older mothers are also at higher risk of pregnancy and birth complications.

Pregnancy and birth

Pregnancy and, to a lesser extent, early infancy appear to be crucial periods when brain development may be affected. Bacterial or viral infections in the mother during pregnancy have been found to slightly increase the risk of autism however this is only a minor factor.

Other factors in the mother that could be related to offspring autism include a folic acid deficiency, gestational diabetes and the use of certain antidepressants during pregnancy, but no conclusive evidence exists for any of these links.

Conversely, taking prenatal vitamins seems to decrease the risk.

Environmental causes

In the past decade there has been increased research into the aspects of our environment that may also contribute to autism. However, despite substantial research, no one environmental factor has yet been found to be a definite cause of autism.

What doesn't cause autism?

Bad parenting

There was a bleak period in history from the 1950s to 1970s when autism was believed to be a psychological disorder, and blamed on cold, uncaring parents, usually the mothers.

Fortunately, the myth of the ‘refrigerator mother’ has been debunked by science, and autism is now recognised as a disorder of brain development with genetic links. Nothing you said or did as a parent caused your child to develop autism, so please don’t listen to anyone who suggests otherwise.

Vaccines

Scores of scientific studies have effectively ruled out vaccines as a cause of autism. Concerns originally arose around two issues of Mercury and the MMR Vaccine (Measles, mumps Rubella)

In 2014, a meta-analysis, combining the result of 10 studies and over 1.2 million children, found no link between vaccines and autism. The World Health Organization, the European Medicines Agency, the American Academy of Pediatrics and other leading international health groups have also concluded there’s no link. Unfortunately, the belief persists among anti-vaccination campaigners, who are very vocal on the Internet. If you remain concerned about vaccines, arrange a time to talk your paediatrician or GP. Remember, Vaccines Save Lives!

Helpful Links and Resources

The Complete Autism Handbook — Benison O’Reilly and Kathryn Wicks (available as a print or eBook)

Having another child when your child has ASD — Raising Children Network

What causes autism? What we know, don’t know and suspect — Dr Andrew Whitehouse at The Conversation.

Vaccination and autism fact sheet — Australian Government Department of Health

National Centre for Immunisation Research and Surveillance (NCIRS) also has a range of fact sheets on vaccine safety

Vaccines still don’t cause autism – Science Based Medicine