What causes autism?

We don’t know exactly what causes autism. There might be several causes, including brain development and genetic factors. Researchers are continuing to study the causes of autism.

Brain development and autism

In young children, the 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’re ‘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, like walking, talking or understanding emotions.

In autistic children, the brain tends to grow faster than average during early childhood, especially during the first 3 years of life. The brains of autistic babies appear to have more cells than they need, as well as poor connections between the cells.

Also, pruning doesn’t seem to happen as much in autistic children. This means that 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 in autistic children than in typically developing children.

It’s not yet clear what causes this variation in brain development.

Autism is a type of neurodivergence, which is the naturally occurring variation in how the brain develops and processes information.

Genetics and autism

In some families, there seem to be more autistic people than in others. This suggests that genes might be one cause of autism. Evidence for this idea has been increasing over the past few decades.

It’s unlikely that there’s one specific gene that causes autism. 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 autism. But they don’t yet understand what causes autism or increases children’s chances of developing it.

The most recent research suggests that genes play a stronger role in causing autism than environmental factors.

Autism can also happen together with other genetic conditions.

‘Neurexine 1’ is an example of a gene identified in autistic people. This is a gene we all have, and it’s important for communication within the brain. Problems or changes in this gene are a known factor in autism. But because the change by itself is not enough to cause autism, it means there must be other factors involved in causing autism.

Other factors and autism

In addition to genes, several other factors have been linked to an increased likelihood of autism. These factors might also trigger autism in a child who’s genetically more likely to develop the condition:

  • older parents
  • poor growth of the foetus in the womb
  • lack of oxygen when a baby is born
  • premature birth
  • exposure to air pollution during pregnancy.

These factors might increase the likelihood of autism, but an increased likelihood isn’t the same as a cause. Not everyone with these environmental factors will be autistic, and some children with none of these factors might be autistic.

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