HEADLINES Published March13, 2015 By Bernadette Strong

A Study of Twins Shows that Up to 95% of Autism Is Due to Genetic Influence

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Autism may be almost completely due to genetic factors.
(Photo : Andrew H. Walker, Getty Images)

A study of twins has found that genetic influences may be playing a larger role in autism that previously thought. The study found that genes may be responsible for from 76% to 95% of the condition.

Researchers in England set out to establish the relative contributions of genetic and environmental factors in the development of autism spectrum disorder. They looked at data on every set of twins born in England and Wales between January 1994 and December 1996. All the children underwent diagnostic measures of assessment for autism or a measure of autistic traits, with about 200 sets of twins were given a best-estimate diagnosis. The study included twins with a high, but subclinical level of the traits associated with autism, low-risk twins, as well as those diagnosed with autism spectrum disorder.

The researchers found 181 of the twins had autism, but the risk was far higher in identical twins.  They found that on all measures of autism spectrum disorder, the associations between identical twins-twins who developed from a single fertilized egg and share virtually identical genes-was higher than fraternal twins-those who developed from two different eggs and have some but not all genes in common. All of the twins had been raised in the same house by their parents, which means that they lived in the same environment.

Hundreds of genes appear to have an effect in autism, the researchers noted. Even so, they did not rule out that environmental factors may play a role in autism.

All the evidence points to genes playing a bigger role in autism than previously thought, said Francesca Happe, PhD., of King's College London and an author of the study. Some people think environment plays a role because the number of children diagnosed with autism has grown rapidly. "The main consensus now is that the rise in diagnosis has more to do with increased awareness of the condition," she told the BBC.

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