Toward an Emerging Paradigm for Understanding Attention-Deficit/Hyperactivity Disorder and Other Neurodevelopmental, Mental, and Behavioral Disorders
2018 Study Abstract
In Association of Exposure to Diethylstilbestrol During Pregnancy With Multigenerational Neurodevelopmental Deficits, Kioumourtzoglou et al use an approach that is as important as it is underused: an examination of multigenerational transmission of environmental associations. That approach may be the most important from an epidemiological perspective. They report that pollutant exposure to grandparents conveys a 30% increase in risk of ADHD in grandchildren. The findings are novel and contribute to this emerging shift in the understanding of mental and behavioral disorders such as ADHD. The size of the association, similar to many other concurrent risk factors for ADHD, is striking.
Although, as the authors note, the dosages of everyday individual environmental pollutants are generally lower (in developed countries at least) than the dosages of diethylstilbestrol they studied, today’s population is exposed to hundreds of poorly studied, neurodevelopmentally or hormonally active compounds, the interactions among which are unknown. Thus, the actual associations today are difficult to quantify.
The limitations in this study should not be overlooked—genetic associations were not able to be examined (so a genotype-environment correlation might partially account for findings), causality could not be evaluated because of the absence of F1 siblings, and ADHD assessment is limited in population studies. Their finding of a first trimester bias in the association, in particular, should be interpreted very cautiously; the incidence of ADHD in the second, third, and first trimester exposures were all higher than the unexposed group, and the statistical power to detect between-trimester associations was low. As the authors appropriately noted, further work on trimester-specific associations will be of interest. Finally, an epigenetic transmission is not the only possibility (because of third-generation oocyte exposure, as the authors noted), although epigenetic transmission by neuroactive chemicals to the third generation is demonstrated in nonhuman animals.
- Toward an Emerging Paradigm for Understanding Attention-Deficit/Hyperactivity Disorder and Other Neurodevelopmental, Mental, and Behavioral Disorders, JAMA Pediatrics doi:10.1001/jamapediatrics.2018.0920, July 2018.
- Featured image credit Jason Leung.