Browsing by Subject "behavior genetics"

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    Genetic And Environmental Influences On DSM-5 Maladaptive Personality Traits And Their Connections With Normative Personality Traits
    (2016-12) Wright, Zara
    The Diagnostic and Statistical Manual for Mental Disorders, 5th Edition (DSM-5) proposes an alternative model for personality disorders, a key element of which is pathological traits. These traits can be operationalized by the Personality Inventory for the DSM-5 (PID-5). Although there has been extensive research on genetic and environmental influences on normative personality, the heritability of the DSM-5 traits, and maladaptive personality in general, remains understudied. The present study addresses this gap in the literature by assessing traits indexed by the PID-5 and the International Personality Item Pool NEO (IPIP-NEO) in adult twins (N = 1,812 individuals). Research aims included 1) replicating past findings of heritability of normative personality as measured by the IPIP-NEO as a benchmark for studying maladaptive traits, 2) ascertaining univariate heritability estimates of maladaptive personality traits as measured by the PID-5, 3) establishing how much variation in maladaptive personality can be attributed to the same genetic components affecting variation in normative personality, and 4) determining residual variance in maladaptive personality after variance attributable to genetic and environmental components of normative personality has been removed. Results revealed that maladaptive personality traits reflect similar levels of heritability to that of normative personality. Further, maladaptive and normative personality traits that correlate at the phenotypic level also correlate at the genotypic level, indicating overlapping genetic components contribute to variance in both. Nevertheless, we also found evidence for genetic and environmental components unique to maladaptive personality traits, not shared with normative personality.
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    Substance Use Transmission and Outcomes: Using Genetically Informative Research Designs for Causal Inference with Observational Data
    (2019-07) Saunders, Gretchen
    One of the most difficult, yet arguably the most important aspect of research is the issue of causal inference using observational data. For phenotypes like substance use, in which it is impractical or unethical to conduct randomized controlled trials, understanding the causal mechanisms that influence substance use behavior as well as the outcomes caused by these behaviors remains difficult. The current work explores how genetically related samples can be exploited to better understand the causal effects of environmental factors on adult outcomes related to early substance use. In Study 1, polygenic risk scores for alcohol and tobacco use are used to identify a genetic nurture effect of parental smoking initiation on offspring alcohol and tobacco use in a large parent-offspring sample. The effect of parental genotype on offspring use is mediated by parental socioeconomic status (SES), suggesting that rearing SES, or the resources higher SES provide, may causally influence substance use in adolescence. Study 2 is a methodological exploration of co-twin control (CTC) designs, in which an exposure- outcome effect is decomposed into a within-twin pair and between-twin pair effect. A limitation of the CTC design is that it cannot implicitly control for environmental factors that are not perfectly shared within a twin pair, the presence of which may bias CTC findings. We use analytical derivations and simulations to show that while inclusion of a covariate as a proxy measure of a non-shared environmental confounder will always reduce bias, results from CTC studies will continue to be biased away from the null to at least some extent in most practical situations. Interpretation and suggestions for use of CTC, and more generally between-within, models are discussed. Finally, in Study 3 we use a large sample of twins to investigate the adult socioeconomic outcomes related to adolescent substance use. Using the co-twin control (CTC) design we find that within monozygotic (MZ) twin pairs, who share all genetic and common environmental factors, the twin who consumes more tobacco and alcohol in adolescence has lower educational attainment and occupational status in adulthood compared to their lesser using co-twin, consistent with a causal effect of early substance use on later socioeconomic outcomes. We focus on interpretation of these results in the context of findings from Study 2.