What causes Autism Spectrum Disorder (asd)? Dr Avril V brereton and Dr Kerry j bull

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What causes Autism Spectrum Disorder (ASD)?

Dr Avril V Brereton and Dr Kerry J Bull

ASD has no single known cause. Given its complexity and the fact that symptoms and severity vary, there are probably many causes including a range of genetic and environmental risk factors.

Genes and environment

Theories about what might cause ASD have changed over the past sixty years. In some families, there appears to be a pattern of ASD or other disabilities. 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 develop1.

Evidence supporting a significant genetic contribution to ASD has been increasing over the past few decades, but what causes or increases the risk for ASD is not yet understood2.

Studies have shown that among identical twins, if one child has an ASD, then the other will be affected between 36-95% of the time. In non-identical twins, if one child has an ASD, then the other is affected between 0-31% of the time.

The patterns of genetic inheritance are complex, with the involvement of multiple genes, rather than a simple dominant, recessive or X-linked gene2. A number of chromosome regions are likely to contain risk genes for ASD, and no gene has been unequivocally identified to date3.

Research has begun to show that environmental factors may also involve some genetic susceptibility. A recent study shows that at an individual level, the risk of autism increases according to how close you are genetically to other relatives with autism4.

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