By Raising Children Network
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Happy little boy with mum in background credit Heagney
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We don’t yet know exactly what causes autism spectrum disorder (ASD). In fact, it’s suspected that there might be several causes. Among these are brain development and genetic factors. ASD is not caused by anything that parents do or don’t do while raising their child.

Brain development and autism spectrum disorder

In children with autism spectrum disorder (ASD), the brain develops differently from typically developing children:

  • The brain tends to grow too fast during early childhood, especially during the first three years of life.
  • The brain of an infant with ASD appears to have more cells than it needs, as well as inefficient connections between the cells.

Too many connections
It’s thought that the characteristic behaviours of ASD come from difficulties with how the brain processes information (especially if the affected areas of the brain are those responsible for understanding emotions and language).

A young child’s brain is developing all the time. Every time a child does something or responds to something, connections in the brain are reinforced and become stronger. Over time, the connections that aren’t reinforced disappear – they are ‘pruned’ away as they’re not needed.

This ‘pruning’ is how the brain makes room for important connections – those needed for everyday actions and responses. It’s thought that, in children with ASD, this pruning doesn’t take place as much as it should – so information might be lost or sent through the wrong connections.

The lack of pruning might also explain why the brain seems to be growing faster than in typical development.

Genetics and autism spectrum disorder

Genetic factors seem to play a major part in autism spectrum disorder (ASD).

For example, some families have multiple children diagnosed with ASD. Many of these families have higher rates of language and anxiety disorders. Siblings of children with ASD often show some ASD traits themselves. ASD also happens in four times as many boys as girls. 

One specific gene is unlikely to be responsible for ASD. Rather, it might be that several genes combine and act together. Researchers have found many possible genes that might play a role in the development of ASD.

It’s also possible that different gene combinations might explain the differences seen in ASD – for example, why one child is more sensitive to sounds than another. 

ASD can also occur together with other genetic conditions, such as Fragile X syndrome.

One example of a gene identified in people with ASD is ‘neurexine 1’. This is a gene we all have, and it’s important for communication within the brain. Problems (or ‘disruptions’) in this gene are a known problem in ASD. But because the disruption by itself is not enough to cause ASD, this is an example of how multiple factors might be involved in causing ASD.

What about environmental factors?

To date, there is no solid evidence to show that ASD can be caused by anything in the environment, such as diet (either during pregnancy or once a child is born) or exposure to certain toxins. It is thought, however, that external factors might trigger ASD in a child who is already genetically prone to developing the condition.

Video Early signs of autism spectrum disorder

In this short video, parents talk about noticing the early signs of autism spectrum disorder (ASD) in their children, including differences in typical developmental behaviour and milestones. They say that it helps to understand developmental milestones so you can act if you’re worried or you think something is wrong. The earlier you act, the better off your child will be.
  • Last updated or reviewed 20-11-2013
  • Acknowledgements This article developed in collaboration with Cheryl Dissanayake and Cherie Green, Olga Tennison Autism Research Centre, La Trobe University.