Commentary: 'Unhealthy diet,' nutrient status, and ADHD symptoms: a confounding role for environmental nitrous oxide exposure - reflections on Rijlaarsdam et al. (2016)

Epigenetics and ADHD: Toward an Integrative Approach of the Disorder Pathogenesis

OBJECTIVE

Epigenetic hypothesis is one of the research pathways used to explain the complex etiology of neurodevelopmental disorders. This review highlights the findings of recent studies in the field of epigenetics in ADHD.

METHODS

An electronic literature search using Medline.

RESULTS

In the Gene × Environment interaction model, several clinical, genetic and molecular arguments support the epigenetic hypothesis in ADHD etiology. Environmental ADHD risk factors including toxic, nutritional factors and stressful life events lead to changes in DNA methylation and in histone modification levels. One critical CpG site located in the promoter of the DRD4 gene exhibited a specific pattern in ADHD children. A methylome wide exploration of DNA showed decreased methylation in vasoactive intestinal peptide receptor 2 gene, which was not replicated by further research.

CONCLUSION

Current data require consolidation and could lead to the identification of biomarkers and the introduction of new modalities of treatment.

Environmental factors influencing the link between childhood ADHD and risk of adult coronary artery disease

Yorbik et al. reported novel findings regarding a hypothesized relationship between childhood attention-deficit hyperactivity disorder (ADHD) and later risk for coronary heart disease in adulthood. The authors found that mean platelet volume (MPV), a marker of platelet reactivity and a presumable biomarker in patients with cardiovascular disease, was significantly elevated in children with ADHD compared to healthy controls. The mechanistic importance of this novel discovery remains unknown and warrants clarification. We have made the novel proposition that environmental exposure to the agricultural and combustion air pollutant, nitrous oxide (N₂O), may be an etiological contributor to neurodevelopmental disorders. Clinical studies suggest that N₂O may enhance platelet hyperaggregation, possibly via its biphasic role as an MAO inhibitor especially at trace levels of exposure or via the generation of oxidative stress. Therefore, this correspondence briefly details the hypothesis that altered biochemical profiles in neurodevelopmental disorders, derived from chronic environmental exposure to the agricultural and combustion air pollutant, N₂O, may promote coronary artery disease in adulthood.