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Genetics Contribute to Autism More than Environment, Study Finds

Genetics contribute to autism more than environmental factors, according to a new study conducted by researchers at the Karolinska Institutet in Stockholm, Sweden. The study, which analyzed data from thousands of pairs of twins in the Swedish Twin Registry and Sweden’s Child and Adolescent Twin Study, found that genetics account for roughly 93% of the chance that a person has autism, and 61 to 73% of the odds that an individual will display autistic traits. The figures are consistent with previous studies showing that genetics play a major role in autism and suggest that environmental factors are unlikely to explain the rise in autism prevalence.

Mark Taylor, senior research specialist at the Karolinska Institutet, led the study, and described it as groundbreaking for being the first to explore whether the genetic and environmental factors behind autism have changed over time. For the study, Taylor and his team analyzed data from 22,678 pairs of twins in the Swedish twin registry, born between 1982 and 2008, and 15,280 pairs of twins from the Child and Adolescent Twin Study. The researchers divided the two groups into cohorts based on when the children were born. Five birth cohorts were created from the registry group, and four were created from the study group. 24% of the twins in the registry group were identical, while 30% of those in the study group are identical.

The researchers identified the children with autism among the twin pairs and confirmed their diagnoses using case notes, health records, or phone interviews with parents and caregivers. To estimate the impact of genetics and the environment on both groups, the researchers compared differences between identical and fraternal twin pairs. They then examined whether these proportions changed from one birth cohort to the next. Ultimately, the team found that in all of the birth cohorts, there were more identical twin pairs in which both twins have autism than fraternal ones. This suggests that genetic factors contribute more strongly to autism than environmental ones, since there would be more behavioral similarities among fraternal twins if the opposite were true. For reference, identical twins share almost all of their genetic code, while fraternal twins share about 50 percent. The results of the study were published May 6 in the journal JAMA Psychiatry.

For their next phase, the researchers plan to focus on environmental factors they had previously linked to autism, to see whether the influence of those factors has changed over time. They also plan to focus on other conditions similar to autism that have become more or less prevalent.



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