Determinants of Personality and Its Association with Risky Health Behaviors

Abstract

Personality plays an important role in almost every aspects of individuals psychosocial and physical health. Additionally, an individuals personality affects health by predisposing the person to a higher chance of developing specific health behaviors. Attention to personality trait in clinical interventions is stressed in many reported health behavioral theories. Temperament and Character Inventory (TCI) is a comprehensive personality inventory that is widely used in behavioral genetics. The original theory suggested that temperament traits were under genetic influences, whereas character traits were gradually built by an interaction between temperaments and environment until early adulthood. Heritabilities of personality has been reported to be about 0.4 in average, but discrepancies in different ethnicities are present, and these estimates tend to be inflated when only twins are used in the study. Also, despite moderate heritability of 0.3-0.6 for most personality domains, even large powered studies with Caucasian samples were not successful in locating specific genetic variant that explains personality. Besides identifying the determinants of personality, confirming its relationship to risky health behaviors, specifically with behaviors that are theorized to have psychosocial base, may give important public health implications. Additionally, personality may mediate the effects of gene on these health behaviors. This study attempted to evaluate TCI by examining the genetic and environmental contributions to personality with particular attention to spousal effects. Also, a genome-wide search for both TCI domains and multivariable TCI-Five-Factor Model (FFM, for sub-samples) were conducted in a population cohort of Korea, where cultural environments are different from Western populations. Lastly, individual personality traits or their linear combinations were tested for associations with health behaviors, such as eating behaviors, nicotine dependency, and alcohol dependency. Interacting effects between personality and genetic variants, which are reported to be related to psychosocial traits, on these health behaviors were explored. This study includes a total of 3,479 individuals (1419 men, 690 families, 552 monozygotic twins, 119 dizygotic twins) from the Healthy twin study of Korea with detail epidemiologic, clinical information and TCI measures. Intraclass correlation coefficients (ICCs) and heritability were calculated to examine the genetic and shared environmental contributions to personality. Among these participants, 3,428 subjects with TCI measures were included in the univariate genome-wide association test. A total of 1,169 individuals (476 men) also fulfilled the FFM measures. Two platforms (Affymetrix Genome-Wide Human array 6.0, Illumina Infinium Humancore Beadchips) were used for genotyping and the markers were imputed using 1kG Asians. For univariate analysis, a family-based association test using mixed-effect variance component approach was conducted. For multivariable analysis of TCI-FFM model, multiple family-based quasi-likelihood score test (MFQLS) was performed to estimate the association of genetic variant to multiple phenotypes in linear mixed model. Linear association was tested for TCI traits and health behaviors adjusting for age, gender, education, income level, and familial correlation. For health behavior traits, Dutch Eating Behavior Questionnaire (DEBQ, n=3,444), Fagerstorm Test for Nicotine Dependence (FTND, n=1,192), and Alcohol Use Disorders Identification Test (AUDIT, n=2,431) were measured. Factor Analysis on particular personality traits (novelty seeking (NS), self-directedness (SD), Cooperativeness (CO)) that were commonly observed to be associated with the targeted health behaviors were conducted using principal axis analysis, and the identified personality patterns were also tested for associations with health behaviors. A total of 183 genetic variants that were reported to be related with neuro-psychological traits were tested to see if they have gene-by-personality (GxP) effect on the health behaviors. Moderate genetic contributions (0.15-0.44) were found for all TCI traits along with the evidence of shared environment (0.12-0.29) for harm avoidance (HA) and all characters. The ICCs of TCI in MZ pairs ranged 0.36-0.45. Spouses had little resemblance for temperament, whereas for character dimensions, spouses (0.27-0.38) were more similar than first degree relatives (0.10-0.27). Resemblance between spouses increased with duration of marriage for most characters and HA. When the growing similarities between spouses were compared with their MZ cotwins for subgroup of 84 trios, self-directedness (SD) of character showed even more similarities toward their spouses than cotwins as partnership duration increased (r=0.29). Univariate TCI domain analysis CO domain were associated with ADAMTS17 gene (Chromosome 15, p= 9.0e-8), but other domains did not reach genome-wide significance level. For agreeableness of FFM, CDH13 gene (Chromosome 16, p=2.8e-7) had marginal p-value, and the same variant had association with agreeableness in previous reported study (p=0.046). In multivariate analysis, SD (TCI) and neuroticism (FFM) showed significant genetic associations in RP11-274B18.4 gene (r=-0.56, Chromosome 9, p= 7.52e-9). All seven TCI traits showed association with some targeted behaviors. Among them, combination of high NS, low SD, and low CO was observed in emotional eating, external eating, nicotine dependence, and alcohol dependence. The subscales of these traits were factorized to obtain specific personality profile named Vulnerability, and its association with, as well as its ability to predict risky health behaviors was also observed. SNAP25 gene interacted with self-transcendence in its association to emotional eating, EVL gene interacted with SD on effect of external eating, and CACNA1C gene interacted with CO to affect FTND. The findings with regard to change in SD into late adulthood support the psychobiological theory of temperament and character, which suggests that both personality domains have distinct developmental trajectories despite equally large genetic influences. Also novel genetic loci were found to be associated personality traits, particularly in character dimensions. The findings from genome-wide search for associated gene illustrates that there may be different biological background in Koreans, and that a multiple measures of personality traits might better capture the genetic architecture of personality traits. Lastly, by finding the personality patterns and GxP effects that have shown increased risk in developing certain health behaviors, translating them into personalized medicine for effective prevention and intervention for risky health behaviors is possible.