A study of more than 1 million pregnancies in Finland is the first to find a connection between an insecticide and autism diagnosis.
The study reports that elevated levels of the metabolite DDE of the banned insecticide DDT in the blood of pregnant women is linked to increased risk for autism diagnosis in babies. The results of the study were published in the American Journal of Psychiatry and the study was conducted by an international research team led by Columbia University’s Mailman School of Public Health and the Department of Psychiatry. Additional researchers included the University of Turku and the National Institute of Health and Welfare in Finland.
Using maternal biomarkers of exposure, the group has been able to link DDT with risk for autism. Maternal blood was taken during early pregnancy and analyzed for DDE, a metabolite of DDT and PCBs, another type of environmental pollutant.
“In pregnant women, they (the pollutants) are passed along to the developing fetus,” said lead author Alan S. Brown, MD, MPH, professor of Epidemiology at Columbia University’s Mailman School of Public Health and of Psychiatry at Columbia University Medical Center. “Along with genetic and other environmental factors, our findings suggest that prenatal exposure to the DDT toxin may be a trigger for autism.”
They identified 778 case of autism among babies born from 1987 to 2005 to women enrolled in the Finnish Maternity Cohort. This represents 98 percent of pregnant women in Finland. These mother and baby pairs were compared to a control group of mothers and babies without autism.
The odds of having a baby with autism with intellectual disabilities doubled for the mother’s with DDE levels in the top quarter of participants. For a general sample of autism cases, the odds for having a baby with autism were nearly 1/3 higher for mother’s with elevated DDE levels.
The findings continued even after several factors were adjusted, including maternal age and psychiatric history. No impact was found between mother with elevated PCBs and autism.
While DDT and PCBs are banned in many countries – including the United States and Finland – they are still persistent in the food chain because they breakdown very slowly. It can take decades for these pollutants to breakdown, resulting in continued exposure. The chemicals are transferred to the placenta during pregnancy in concentrations greater than those in the mother’s blood stream.
“We think of these chemicals in the past tense, relegated to a long-gone era of dangerous 20th Century toxins,” Brown said. “Unfortunately, they are still present in the environment and are in our blood and tissues.”
When looking an DDE affects versus PCBs, the researchers offered two more reasons that DDE may be more of a contributing factor.
- Maternal DDE is associated with low birthweight, a well-replicated risk factor for autism. PCB exposure has not been related to low birthweight.
- Androgen receptor binding is a process significant to neurodevelopment. A study in rats found DDE inhibits androgen receptor binding, which is an outcome that is also seen in a rat model of autism. PCBs have been found to increase androgen receptor.
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