Using Hierarchical Measures of Psychopathology to Capture the Effects of Environmental Stressors and Gene-Environment Interplay
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GxE = ‘p’? Using Hierarchical Measures of Psychopathology to Capture the Effects of Environmental Stressors and Gene-Environment Interplay by Jonathan D. Schaefer Department of Psychology & Neuroscience Duke University Date:_______________________ Approved: ___________________________ Terrie Moffitt, Supervisor ___________________________ Avshalom Caspi, Co-supervisor ___________________________ Margaret Sheridan ___________________________ William Copeland ___________________________ Timothy Strauman Dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Psychology & Neuroscience in the Graduate School of Duke University 2019 ABSTRACT GxE = ‘p’? Using Hierarchical Measures of Psychopathology to Capture the Effects of Environmental Stressors and Gene-Environment Interplay by Jonathan D. Schaefer Department of Psychology & Neuroscience Duke University Date:_______________________ Approved: ___________________________ Terrie Moffitt, Supervisor ___________________________ Avshalom Caspi, Co-Supervisor ___________________________ Margaret Sheridan ___________________________ William Copeland ___________________________ Timothy Strauman An abstract of a dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Psychology & Neuroscience in the Graduate School of Duke University 2019 Copyright by Jonathan D. Schaefer 2019 Abstract Exposure to psychosocial stress is a robust predictor of subsequent psychopathology. However, only a portion of individuals with these experiences will develop psychiatric symptoms. The concept of gene-environment interaction (GxE) has provided one theoretical framework for reconciling these observations, but the empirical findings from this literature are mixed and often fail to replicate across studies. This dissertation explores the use of a relatively new approach to measuring the mental-health effects of environmental stress (the “p-factor”), and examines whether this approach has the potential to advance and consolidate studies of gene-environment interaction and psychopathology. First, I present lifetime prevalence data from The Dunedin Multidisciplinary Health and Development Study indicating that mental disorder is near- ubiquitous, consistent with the notion that liability to these conditions is distributed quantitatively throughout the population. Second, I present analyses from the Environmental Risk Longitudinal Twin Study showing that the mental-health effects of victimization exposure (one of the most common and severe types of psychosocial stress) are both non-specific and likely causal. These data suggest that stressful life experiences increase risk of psychopathology largely through effects on general liability. Third, I examine whether victimization’s effects on general psychopathology vary as a function of multiple measures of genetic propensity. Results consistently indicate that they do not, suggesting minimal gene-environment interaction. Implications for future research that seeks to identify the genetic and non-genetic factors that determine vulnerability and resilience to the mental-health effects of environmental stress are discussed. iv Dedication Dedicated to the memory of Daniel Colby Weston—cadet, comedian, and friend. “I used to get a big kick out of saving people’s lives. Now I wonder what the hell’s the point, since they all have to die anyway.” “Oh, there’s a point, all right,” Dunbar assured him. “Is there? What’s the point?” “The point is to keep them from dying as long as you can.” - Joseph Heller, “Catch-22” v Contents Abstract............................................................................................................................. iv List of Tables .................................................................................................................... xi List of Figures ................................................................................................................ xiii Acknowledgments ......................................................................................................... xv Chapter 1. General Introduction .................................................................................... 1 1.1 The many “Gs” in “GxE” research: from family history to candidate genes to cumulative genetic risk measures ....................................................................... 3 1.1.1 Family history approaches ........................................................................ 3 1.1.2 Candidate gene approaches ...................................................................... 5 1.1.3 Genome-wide approaches ......................................................................... 7 1.1.4 Latent genetic propensity approaches ................................................... 11 1.2 Embracing “p”: The case for a transdiagnostic, continuous psychiatric phenotype.................................................................................................................. 13 1.2.1 Dimensionality .......................................................................................... 15 1.2.2 Comorbidity ............................................................................................... 17 1.2.3 Genetic overlap .......................................................................................... 18 1.2.4 Non-specific environmental effects ........................................................ 23 1.2.5 Predictive power ....................................................................................... 27 1.3 Criticisms of the p-factor ................................................................................... 28 1.3.1 The interpretation of latent factors in hierarchical models of “p” are unclear ................................................................................................................. 29 1.3.2 The meaning of “p” likely differs depending on the underlying indicators used ................................................................................................... 30 vi 1.3.3 Fit statistics are biased in favor of the bi-factor model ........................ 32 1.4 Specific study objectives ................................................................................... 34 Chapter 2. Enduring Mental Health: Prevalence and Prediction .......................... 37 2.1 Introduction ........................................................................................................ 38 2.1.1 A qualitative review of the prevalence of not having a mental disorder................................................................................................................ 40 2.1.2 Empirical study of individuals with enduring mental health ............ 43 2.2 Methods ............................................................................................................... 44 2.2.1 Sample ........................................................................................................ 44 2.2.2 Assessment of mental disorders ............................................................. 45 2.2.3 Candidate childhood predictors ............................................................. 46 2.2.4 Midlife outcomes ....................................................................................... 47 2.3 Results .................................................................................................................. 48 2.3.1 Defining mental-health histories over the first half of the life course 48 2.3.2 Informant reports: To what extent do they confirm the enduring mental health of never-diagnosed Study members? .................................... 50 2.3.3 What distinguishes Study members who experienced enduring mental health from those who experienced “typical” mental health histories? .............................................................................................................. 51 2.3.4 Is enduring mental health associated with more desirable life outcomes (i.e. greater educational and occupational attainment, increased life satisfaction, and higher-quality relationships)? ...................................... 54 2.4. Discussion .......................................................................................................... 54 2.4.1 Limitations ................................................................................................. 58 2.4.2 Implications and future directions ......................................................... 59 vii 2.4.3 Conclusions ................................................................................................ 61 Chapter 3. Adolescent Victimization and Early-Adult Psychopathology: Approaching Causal Inference Using a Longitudinal Twin Study to Rule out Non-Causal Explanations ............................................................................................. 78 3.1 Introduction ........................................................................................................ 79 3.2 Methods ............................................................................................................... 85 3.2.1 Study sample ............................................................................................. 85 3.2.2 Measures..................................................................................................... 86 3.2.2.1 Assessment of victimization exposure .........................................