So: “After controlling for ethnicity, gender, and socioeconomic factors, the strongest predictor of ASD [autism spectrum disorders] was the rate of male congenital malformations of the reproductive system, used as an approximate measurement for exposure to teratogens, based on extensive epidemiological evidenceâ€.
That was one of the conclusions reached by the study by Andrey Rzhetsky and colleagues [1] (open-access) which looked at spatial incidence patterns of autism and intellectual disability (ID) based on an insurance claims database in the United States.
The media have been pretty much all over this study as per headlines such as: “Growing Evidence That Autism Is Linked to Pollution†and “Autism disorders greatly linked with environmental factors, study claims“. That last headline comes complete with a picture of someone spraying crops, I assume intended to link something like pesticide use and the increase in cases of autism which we’ve witnessed over the past decades. I’m slightly unsure however that this is the best picture to use in this particular case though (see here).
The details of the Rzhetsky study are pretty widely available (including in the paper which is open-access) but a few points might be of interest:
- As the publishing journal title suggests, this was a study based on statistics and data. Researchers based their analysis on the Truven Health Analytics MarketScan Commercial Claims and Encounters Database which includes data on some 138 million people dating back from 1995. They scanned approximately 105 million patient records collected between 2003 and 2010 for the purposes of their study.
- As well as collecting data on variables like gender and ethnicity, they looked at various variables according to “eligibility in special education programs under the Individuals with Disabilities Education Act†to ascertain cases of autism and intellectual disability, and the spatial incidence patterns according to county-level geography within the United States.
- Using data on the rate of congenital malformation of the reproductive system (genitals) for males and females and other variables related to viral exposures as “county-level environmental indicators“, they examined whether such surrogate markers of environmental exposures tied into the rates of autism.
- Results: yes, quite a few of them. “Adjusted for gender, ethnic, socioeconomic, and geopolitical factors, the ASD incidence rates were strongly linked to population-normalized rates of congenital malformations of the reproductive system in males (an increase in ASD incidence by 283% for every percent increase in incidence of malformations, 95% CI: [91%, 576%], p6×10?5)“. What this translates as is that for every 1% increase in male genital malformation, there was a 283% increase in autism in the same area. This compared with only a 94% increase for ID.
- Big quote coming up… “The estimated county-level random effects exhibited marked spatial clustering, strongly indicating existence of as yet unidentified localized factors driving apparent disease incidence“. Ergo something(s) environmental potentially driving the increase in cases of autism.
[6]Â Frazier TW. et al. A Twin Study of Heritable and d Environmental Contributions to Autism. J Autism Dev Disord. 2014 Mar 7.
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