How does the social environment 'get into the mind'? Epigenetics at the intersection of social and psychiatric epidemiology

Abstract

The social environment plays a considerable role in determining major psychiatric disorders. Emerging evidence suggests that features of the social environment modify gene expression independently of the primary DNA sequence through epigenetic processes. Accordingly, dysfunction of epigenetic mechanisms offers a plausible mechanism by which an adverse social environment gets "into the mind" and results in poor mental health. The purpose of this review is to provide an overview of the studies suggesting that epigenetic changes introduced by the social environment then manifest as psychological consequences. Our goal is to build a platform to discuss the ways in which future epidemiologic studies may benefit from including epigenetic measures. We focus on schizophrenia, major depressive disorder, post-traumatic stress disorder, anorexia nervosa, and substance dependence as examples that highlight the ways in which social environmental exposures, mediated through epigenetic processes, affect mental health.

Figure 1

Proportion of variance attributable to genetic and environmental effects according to twin studies of schizophrenia, MDD, PTSD, AN, AD, and DA. Sch: Schizophrenia (Cardno & Gottesman, 2000); MDD: Major Depressive Disorder (Kendler & Prescott, 2007); PTSD: Post-traumatic Stress Disorder (Stein et al., 2002); AN: Anorexia Nervosa (Bulik et al., 2006); AD: Alcohol Dependence (Kendler & Prescott, 2007), DA: Drug Abuse (Tsuang et al., 1998)

Figure 2

Heat map of disease-related annotations (Huang da, Sherman, & Lempicki, 2009) associated with genes (n=167) in the uniquely unmethylated gene set among those without lifetime PTSD from Uddin (Uddin, Aiello et al., 2010). Results suggest a decrease in activity among genes known to play a role in schizophrenia and other psychiatric diseases in those with lifetime PTSD. BLACK: Corresponding gene-disease association yet not reported. GREEN: Corresponding gene-disease association positively reported.