Incorporating the social environment in genotype environment interaction studies of mental disorders

Gene-by-social-environment interaction (GxSE) between ADCYAP1R1 genotype and neighborhood crime predicts major depression symptoms in trauma-exposed women

BACKGROUND

Few studies have explored interactions between genes and social environmental exposures (GxSEs) for trauma-related psychopathology, including symptoms of posttraumatic stress (PTS) and major depression (MD). The extant literature suggests the possibility of a GxSE between the rs2267735 variant of the ADCYAP1R1 gene and neighborhood crime. The current study aimed to explore this possibility among a predominantly African American sample of trauma-exposed women.

METHODS

Female participants (N=1361) were recruited from a public hospital, and completed measures of PTS and MD symptoms and provided DNA samples. Participants' home addresses were mapped onto 300 neighborhoods (2010 census tracts), and data on crime within neighborhoods was collected.

RESULTS

Multilevel models detected a significant GxSE between rs2267735 and neighborhood crime for MD symptoms (p=.01). Having two copies of the risk (C) allele was associated with higher MD symptoms for participants living in high-crime neighborhoods.

LIMITATIONS

At least six limitations are noteworthy: (1) low statistical power; (2) use of self-report symptom inventories; (3) lack of information on symptom onset; (4) homogeneous sample from a single metropolitan area; (5) non-specific index of crime; and (6) use of census tracts to define neighborhoods.

CONCLUSIONS

The results provide further evidence of GxSEs for psychiatric outcomes among trauma-exposed populations. Further investigations of genetic factors for trauma-related psychopathology should include careful assessments of the social environment.

Epigenetics and social context: implications for disparity in cardiovascular disease

BACKGROUND

Although it is well established that African Americans (AA) experience greater social stressors than non-Hispanic Whites (NHW), the extent to which early life adversity and cumulative social stressors such as perceived discrimination, neighborhood violence, subjective social status, and socioeconomic status contribute to disparity in coronary heart disease (CHD) and stroke between AA and NHW are not well understood.

PURPOSE

The purpose of this paper is to propose a conceptual model based upon McEwen's Allostatic Load Model suggesting how the relationships among social context, early life adversity, psychological stress, inflammation, adaptation, and epigenetic signature may contribute to the development of CHD and ischemic stroke. We hypothesize that social context and prior life adversity are associated with genome-wide as well as gene-specific epigenetic modifications that confer a proinflammatory epigenetic signature that mediates an enhanced proinflammatory state. Exposure to early life adversity, coupled with an increased allostatic load places individuals at greater risk for inflammatory based diseases, such as CHD and ischemic stroke.

RESULTS

Based on a review of the literature, we propose a novel model in which social context and psychological stress, particularly during early life, engenders a proinflammatory epigenetic signature, which drives a heightened inflammatory state that increases risk for CHD and stroke. In the proposed model, a proinflammatory epigenetic signature and adaptation serve as mediator variables.

CONCLUSIONS

Understanding the extent to which epigenetic signature bridges the psycho-social environment with inflammation and risk for CHD may yield novel biomarkers that can be used to assess risk, development, and progression of CHD/stroke. Epigenetic biomarkers may be used to inform preventive and treatment strategies that can be targeted to those most vulnerable, or to those with early signs of CHD, such as endothelial dysfunction. Furthermore, epigenetic approaches, including lifestyle modification and stress reduction programs, such as mindfulness-based stress reduction, offer promise to reduce health inequity linked to social disadvantage, as emerging evidence demonstrates that adverse epigenetic marks can be reversed.

The urban environment and mental disorders: Epigenetic links

For the first time in human history, more than half of the world's population lives in urban areas and this is projected to increase to two-thirds by 2030. This increased urbanity of the world's population has substantial public health implications. Nearly a century of research has shown higher risk of mental disorder among persons living in urban versus rural areas. Epidemiologic research has documented that associations between particular features of the urban environment, such as concentrated disadvantage, residential segregation and social norms, contribute to the risk of mental illness. We propose that changes in DNA methylation may be one potential mechanism through which features of the urban environment contribute to psychopathology. Recent advances in animal models and human correlation studies suggest DNA methylation as a promising mechanism that can explain how the environment "gets under the skin." Aberrant DNA methylation signatures characterize mental disorders in community settings. Emerging evidence of associations between exposure to features of the environment and methylation patterns may lead toward the identification of mechanisms that explain the link between urban environments and mental disorders. Importantly, evidence that epigenetic changes are reversible offers new opportunities for ameliorating the impact of adverse urban environments on human health.