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Environmental factors may affect incidence of autism and intellectual disability

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A new study published today in the journal PLOS Computational Biology surveying nearly one third of the U.S. population finds that there may be a strong correlation between environmental factors and incidence of autism spectrum disorder (ASD) and intellectual disability (ID).

The researchers from the University of Chicago used an insurance claims dataset to analyze spatial incidence patterns of ASD and ID. The rate of congenital malformations in diagnosed children was used as an indicator of parental exposure to various environmental risk factors and toxins.

The authors show that (1) ASD and ID display strong clustering across US counties; (2) counties with high ASD rates also appear to have high ID rates, and (3) the spatial variation of both phenotypes appears to be driven by environmental, and, to a lesser extent, economic incentives at the state level.

When adjusted for gender, ethnic, socioeconomic, and geopolitical factors, results of this analysis indicated incidence rates increased by 283% for ASD and 94% for ID, for every percent increase in incidence of malformations.

In addition, a correlation between ASD and rate of congenital malformations of the genitals in males was also found. This can be attributed to the high susceptibility of male fetuses to parental exposure to environmental toxins, such as lead.

Furthermore, states implementing stricter diagnostic criteria, requiring diagnosis by a pediatrician or clinician, accounted for a decrease of 99% in incidence rates of both ASD and ID. Ease of access to a qualified diagnostician was also cited as a factor in diagnostic reates.

While use of vaccines was not a component of this study, the authors note that the geographic clustering of ASD and ID rates found in the study indicate that vaccines are unlikely to play a role since they are disseminated uniformly across the country.

The study authors also call for future genetic studies to consider geographic locations of where the data is accumulated, since two children with identical genetic backgrounds may yield a diagnosis in one environment but not the other.

Although this study is not experimental in nature and only provides corollary data, expanding the scope of research to include environmental and economic factors, in concert with genetic analyses, will provide a broader picture into possible causes of autism spectrum disorder and intellectual disability.

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