New research suggests environmental factors may cause autism.
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The underlying causes of autism have never been fully understood, although usually health experts have blamed a combination of genetics and environmental factors. Now, a newly released meta-analysis has shown that toxins play a much more significant role in the cause of this neurodevelopmental disorder than previously thought.

Researchers from the University of Chicago published the new study in the journal PLOS Computational Biology, where they examined medical records from more than 100 million people living in the United States.  Their analysis revealed that autism and intellectual disability (ID) rates correlated at the county level with incidences of genital malformations in newborn males. According to the researchers, this association is an indicator of exposure to harmful environmental factors during congenital development.

“Essentially what happens is during pregnancy is there are certain sensitive periods where the fetus is very vulnerable to a range of small molecules – from things like plasticizers, prescription drugs, environmental pesticides and other things,” study author Andrey Rzhetsky, a professor of genetic medicine and human genetics at the University of Chicago, told “…And some of these small molecules essentially alter normal development.  It’s not really well known why, but it’s an experimental observation, especially in boys and especially in the reproductive system.”

Rzhetsky and his team analyzed data from insurance claims covering more than a third of the U.S. population. Their data was from individual states and more than 3,100 counties, comparing autism rates and cases of congenital malformations of the male reproductive system as well as the female system.

After adjusting for gender, ethnic, socioeconomic and geopolitical factors, the researchers found that autism rates increased by 283 percent for every 1 percent increase in frequency of congenital malformations. Intellectual disability rates increased by 94 percent for every 1 percent increase.

“Malformations predict very strongly the rates of autism, and the rate of malformation per person varies significantly across the country,” Rzhetsky said. “Some counties have low rates and some have very high.  And rate of malformations is higher in counties with higher rates of autism.”

As of yet, there is no definitive cause for autism, but Rzhetsky hopes his study will spark a shift in the scientific community from researching mostly genetic causes to researching more environmental factors.