Causes of autism

When a loved one is diagnosed with autism, it’s 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 chance of having another child with autism when compared with the general population. The chance 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 also be affected (77% in one large study). With fraternal (dizygotic) twins, who have a different genetic makeup to each other, the chance is much less.

Google ‘autism and genes’ and you’ll find it’s a thriving area of autism research. Unfortunately, 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) have an increased chance 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 chance 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 chance 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 chance.

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.

“There is a lot of false information on the internet. We need to listen to the professionals and evidence and not get distracted by blame or myths.”

What doesn't cause autism?

Currently, we are more certain about what does not cause autism than what does. Research into the causes of autism has debunked a range of inaccurate theories, many of which have caused great harm to people with autism, their loved ones and the broader community. Below are some of the most common myths around the causes of autism that autistic people and their loved ones should be aware of.

Vaccines do not cause autism

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). The latter was sparked by a study by British physician Andrew Wakefield (and 11 co-authors) published in the esteemed medical journal 'The Lancet' in 1998.  Wakefield’s study has since been roundly discredited and The Lancet later retracted the article.

In 2014, a meta-analysis combining the results 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 to your paediatrician or GP. Remember, vaccines save lives!

Foods do not cause autism

If you have been researching autism on the internet, you are likely to have come across all sorts of diets and supplements that claim to cause or 'cure' autism. There is no scientific evidence that specific foods or diets cause autism.

A common diet discussed in autism circles is the gluten and casein-free diet (GF/CF). This involves removing the proteins found in grains and dairy products from the diet. Some families report improvements in their child’s symptoms when they eliminate these foods. So far, double-blind clinical trials have failed to show the GF/CF diet is effective in reducing behavioural symptoms in autism. However, it’s possible there’s a subgroup of children (probably those with GI problems) who may benefit from a GF/CF diet, but were not picked up in these trials.

Children with autism are often picky eaters and restricting their diet further risks negative health effects including decreased bone density, constipation, nutritional imbalances and malnutrition. Speak with your GP or paediatrician about elimination diets or consult an accredited dietitian or nutritionist, who can ensure your child’s diet is nutritionally sound.

Bad parenting does not cause autism

There was a bleak period in history from the 1950s to the 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.