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Friday, March 28, 2014

An argument for the environmental cause of autism

Although we still don’t have a definitive cause for autism spectrum disorders (ASD), we know there is a strong genetic component. Cases of ASD tend to cluster in families and many specific genes have been implicated. However, that doesn’t mean that those genetic changes weren’t caused by environmental factors that acted during fetal development.

Researchers led by Andrey Rzhetsky of the University of Chicago scoured the insurance claims of roughly one third of the U.S. population looking for incidences of ASD. They compared those rates, county by county across the country, with the rate of birth defects in the reproductive systems of baby boys. The idea was that the birth malformations would indicate whether the parents had been exposed to environmental toxins like pesticides.

Sure enough, regions with higher rates of congenital malformations also had higher rates of ASD. For every 1% increase in birth defects there was a 283% higher incidence of ASD. This suggests that whatever is causing the increase in birth defects is also causing ASD.

To be clear, this is no more than an association. We don’t know for sure that environmental toxins are responsible for causing ASD, let alone which toxins. It is interesting that the male genetic structures form in the fetus at about the same time as neurons appear within the developing brain. Thus, exposure at that time could affect both or either developing organs.

If there is a an environmental factor causing ASD, it is felt prenatally, and perhaps even before conception (if the parents' germ cells were affected). By the time the baby is born, the damage has already been done.

Rzhetsky, A., Bagley, S., Wang, K., Lyttle, C., Cook, E., Altman, R., & Gibbons, R. (2014). Environmental and State-Level Regulatory Factors Affect the Incidence of Autism and Intellectual Disability PLoS Computational Biology, 10 (3) DOI: 10.1371/journal.pcbi.1003518.

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