A condition that affects 1 in 37 boys and 1 in 151 girls in the US, research is fast-showing that genetics account for 81% of the risk factor for someone to develop autism (Autism Speaks: 2018). But how relevant are these findings? And how do they compare with other studies that show other environmental factors may have a strong impact on its incidence?
In a study comprising 2,001,631 children from Denmark, Finland, Sweden, Israel and Australia, researchers concluded that genetic factors account for 81% of the risk factor for the development of autism spectrum disorder (ASD). To this end, they also concluded that environmental factors account for less than 20% of its incidence, with maternal factors, such as the mother’s weight, whether the baby is born during a caesarian section etc., having been found to have a “nonexistent or minimal” effect on the development of ASD (Bai, Dan: 2019).
To report this, the researchers used statistical analysis to assess medical records of participants until they reached 16 years of age. Out of the cohort, 22,156 of them were eventually diagnosed with ASD (Hale, Tome: 2019).
Despite having calculated the percentage risk factor however, the authors of the study caution that the specific genes behind the condition are still unknown, as well as how they may interact with environmental factors. Dr Sven Sandin, a senior author of the research said, “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.”
To this end, beyond further research into identifying the underlying genetic causes of autism, further research is also being conducted to reveal the impact of other factors including diet and infection during pregnancy.
For example, another recent study highlighted a connection between autism and the microbiome. In this case, the study highlighted that high levels of Propionic Acid (PPA), a substance used in processed foods to extend shelf life, seem to reduce neuronal development in foetal brains (Abdelli: 2019).
According to the researchers behind this study, excessive PPA causes a decrease in the number of neurons in the brain while causing excessive production of glial cells. This then leads to inflammation, which damages neuronal pathways that allow the brain to communicate with the body, also a key marker of autism (Beres: 2019).
Although these findings seem to conflict with other research suggesting the negligent impact of maternal factors on the development of ASD, it is worthwhile to note that Abdelli and her team drew their conclusions from in vitro laboratory experiments as opposed to pregnant mothers due to ethical reasons. Although they plan on conducting further experiments on mice to further verify research, this means that their findings as of yet are not conclusive. Moreover, even though researchers Bai et al. studied maternal factors in relation to the incidence of autism, they did not account for the effects of PPA presence during pregnancy, and so rather than being contradictory, both studies may indeed reinforce each other (Davis: 2019).
To conclude, although autism may have a large genetic risk factor, even accounting for 81% of its incidence, the extent to which this is the case is the topic of further research. Moreover, roughly 20% of environmental factors are also still undergoing deeper analysis, both exclusievly and in relation to genetic factors.
Bai, Dan et al. JAMA Psychiatry
Hale, Tom, IFLScience
Abdelli, Latifa S. et al.: Nature
Beres, Derek: Big Think
Davis, Matt, Big Think