In The Politics of Autism, I discuss various ideas about what causes the condition.
Here is just a partial list of correlates, risk factors, and possible causes that have been the subject of serious studies:
• Air pollution and proximity to freeways;
• Maternal thyroid issues;
• Autoimmune disorders;
• Induced labor;
• Preterm birth;
• Birth by cesarean section;
• Maternal and paternal obesity;
• Maternal and paternal age;
• Maternal post-traumatic stress disorder;
• Smoking during pregnancy;
• Antidepressant use during pregnancy.
Chemicals used in certain pesticides and as insulating material banned in the 1970s may still be haunting us, according to new research that suggests links between higher levels of exposure during pregnancy and significantly increased odds of autism spectrum disorder in children.
According to the research, children born after being exposed to the highest levels of certain compounds of the chemicals, called organochlorine chemicals, during their mother's pregnancy were roughly 80 percent more likely to be diagnosed with autism when compared to individuals with the very lowest levels of these chemicals. That also includes those who were completely unexposed.
Although production of organochlorine chemicals was banned in the United States in 1977, these compounds can remain in the environment and become absorbed in the fat of animals that humans eat, leading to exposure.
With that in mind, Kristen Lyall, ScD, assistant professor in Drexel University's A.J. Drexel Autism Institute, and her collaborators, decided to look at organochlorine chemicals during pregnancy since they can cross through the placenta and affect the fetus' neurodevelopment.
"There's a fair amount of research examining exposure to these chemicals during pregnancy in association with other outcomes, like birth weight -- but little research on autism, specifically," Lyall said. "To examine the role of environmental exposures in risk of autism, it is important that samples are collected during time frames with evidence for susceptibility for autism -- termed 'critical windows' in neurodevelopment. Fetal development is one of those critical windows."
Their paper describing this study was titled, "Prenatal Organochlorine Chemicals and Autism," and published in Environmental Health Perspectives.
Blood tests taken from the second trimester of the children's mothers were used to determine the level of exposure to two different classes of organochlorine chemicals: Polychlorinated biphenyls (PCBs, which were used as lubricants, coolants and insulators in consumer and electrical products) and organochlorine pesticides (OCPs, which include chemicals like DDT).
"Exposure to PCBs and OCPs is ubiquitous," Lyall said. "Work from the National Health and Nutrition Examination Survey, which includes pregnant women, shows that people in the U.S. generally still have measurable levels of these chemicals in their bodies."