According to the most comprehensive study of its kind to date, autism is caused largely by genetic factors,
The latest report from the CDC pegs autism rates at 1 in 59 children in the U.S. While the specific causes of autism haven’t been established, researchers have long theorized that the disorder is due to both environmental and genetic factors. Looking at over 2 million people in five different countries, this study concluded that the heritability of autism spectrum disorders are approximately 80%.
That leaves about 20% that could be due to other factors, like environmental ones.
However, environmental factors are often cited as a main cause of autism in the media and in the public, “even when (as in the case of vaccine fears), they are debunked,” wrote three psychiatrists in an editorial accompanying the study. This may be because environmental factors are modifiable, and so the idea of being able to control those factors can have mass appeal to parents.
While genes are the biggest factor, researchers still don’t know which ones in particular affect the risk of a child having ASD. And just because environmental or modifiable factors only influence about 20% of cases doesn’t negate the fact that they do have an impact.
The study was published on July 17, 2019, in the journal JAMA Psychiatry.
Researchers combed the national health registries of children in five countries: Denmark, Finland, Sweden, Western Australia, and Israel. Of the 2,001,631 children studied, 22,156 of them were diagnosed with autism. The health records for Israeli children were pulled from 2000 to 2011, while the other four countries had records pulled from 1998 to 2007.
Because most of the children lived in Denmark, Finland, and Sweden, researchers used those children for the main analysis and looked at the children from Western Australia and Israel separately.
Overall, researchers concluded that about 80% of the risk of developing autism was due to genetics, with the median of ASD heritability settling at 80.8%.
What about the remaining 20%? Researchers found that 18.1% of autism risk was due to unknown environmental factors not shared among family members, including gene mutations that are not inherited. They found that risk factors that were shared among family members, like home environment, generally did not affect autism risk. A “nonexistent or minimal” percentage of risk — hovering around 1% — was due to maternal factors.
However, other studies have linked autism and several different maternal factors, like infection during pregnancy.
This is the third study published in the past decade to support findings that genetic factors are largely responsible for autism risk. Two previous studies — one in 2017 and one in 2010 — published similar results, finding 83% of autism risk and 80% of autism risk was inherited, respectively.
The authors note that this study had its limitations, and that there is still more to uncover.
“There is a lot of work that still needs to be done,” study author Sven Sandin, a statistician and epidemiologist with the Karolinska Institutet in Sweden, told HuffPost. “We still do not know which specific genes contribute to risk. Also, there are numerous potential environmental factors that could be related to ASD either directly or acting together with genes. We have, so far, only been scratching the surface.”
C. Dixon likes to read, sing, eat, drink, write, and other verbs. She enjoys cavorting around the country to visit loved ones and experience new places, but especially likes to be at home with her husband, son, and dog.