The causes of autism spectrum disorder (ASD) are complex and varied. The question of nature versus nurture, or genetic versus environmental causes, has loomed large in the study of autism’s etiology. A recent study finds that genetic factors are a much more significant risk for the development of ASD than environmental factors. In one of the largest twin studies to date, the researchers discovered that genetics could account for as much as 95 percent of the risk for ASD. This is almost double the 50 to 60 percent genetic risk that other studies have put forward.
The study drew data from the Twins Early Development Study, which followed twins born in England and Wales between 1994 and 1996. The researchers selected participants for the present study based on at least one twin in the pair being diagnosed with ASD or having passed a certain threshold on the Childhood Autism Spectrum Test. There were 146 twin pairs in which at least one twin received an initial diagnosis of ASD. The researchers followed up with these children, evaluating them during home visits. They confirmed 141 cases of ASD and identified 40 children with ASD-like traits.
When one twin in an identical twin pair has ASD, the odds of the other twin having ASD are between 62 and 94 percent. For fraternal twin pairs, when one twin has ASD, the odds of the other twin having ASD are between 5 and 61 percent. Based on this data, the researchers’ statistical model showed that genetic influences account for 56 to 95 percent of the risk for ASD. This model also supports the theory that autism-related traits and skills are distributed throughout the population and that people with ASD have a high concentration of these traits. The model does not account for the interaction of genetic and environmental factors.
The study does have some limitations. Notably, the sample consisted of nearly all white people and the whole sample was from the United Kingdom. Despite this, the findings advance what is known about the genetic risk for ASD.
This research is published in JAMA Psychiatry.
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