The genetic structure of personality III. Multivariate genetic item analysis of the EPQ scales

Genetic and neural bases of the neuroticism general factor

We applied structural equation modeling to conduct a genome-wide association study (GWAS) of the general factor measured by a neuroticism questionnaire administered to ∼380,000 participants in the UK Biobank. We categorized significant genetic variants as acting either through the neuroticism general factor, through other factors measured by the questionnaire, or through paths independent of any factor. Regardless of this categorization, however, significant variants tended to show concordant associations with all items. Bioinformatic analysis showed that the variants associated with the neuroticism general factor disproportionately lie near or within genes expressed in the brain. Enriched gene sets pointed to an underlying biological basis associated with brain development, synaptic function, and behaviors in mice indicative of fear and anxiety. Psychologists have long asked whether psychometric common factors are merely a convenient summary of correlated variables or reflect coherent causal entities with a partial biological basis, and our results provide some support for the latter interpretation. Further research is needed to determine the extent to which causes resembling common factors operate alongside other mechanisms to generate the correlational structure of personality.

Genetic and Environmental Structure of DSM-IV Criteria for Antisocial Personality Disorder: A Twin Study

Results from previous studies on DSM-IV and DSM-5 Antisocial Personality Disorder (ASPD) have suggested that the construct is etiologically multidimensional. To our knowledge, however, the structure of genetic and environmental influences in ASPD has not been examined using an appropriate range of biometric models and diagnostic interviews. The 7 ASPD criteria (section A) were assessed in a population-based sample of 2794 Norwegian twins by a structured interview for DSM-IV personality disorders. Exploratory analyses were conducted at the phenotypic level. Multivariate biometric models, including both independent and common pathways, were compared. A single phenotypic factor was found, and the best-fitting biometric model was a single-factor common pathway model, with common-factor heritability of 51% (95% CI 40-67%). In other words, both genetic and environmental correlations between the ASPD criteria could be accounted for by a single common latent variable. The findings support the validity of ASPD as a unidimensional diagnostic construct.

Shared environmental influences on personality: a combined twin and adoption approach

In the past, shared environmental influences on personality traits have been found to be negligible in behavior genetic studies (e.g., Bouchard and McGue, J Neurobiol 54:4-45, 2003). However, most studies have been based on biometrical modeling of twins only. Failure to meet key assumptions of the classical twin design could lead to biased estimates of shared environmental effects. Alternative approaches to the etiology of personality are needed. In the current study we estimated the impact of shared environmental factors on adolescent personality by simultaneously modeling both twin and adoption data. We found evidence for significant shared environmental influences on Multidimensional Personality Questionnaire Absorption (15% variance explained), Alienation (10%), Harm Avoidance (14%), and Traditionalism (26%) scales. Additionally, we found that in most cases biometrical models constraining parameter estimates to be equal across study type (twins vs. adoptees) fit no worse than models allowing these parameters to vary; this suggests that results converge across study design despite the potential (sometimes opposite) biases of twin and adoption studies. Thus, we can be more confident that our findings represent the true contribution of shared environmental variance to personality development.

Evidence for Nonadditive Genetic Effects on Eysenck Personality Scales in South Korean Twins

While evidence supporting for nonadditive genetic influences on personality traits in Caucasian populations has been growing in recent years, twin studies that explored the existence of genetic nonadditivity in personality variation in Asian populations are still lacking. Seven hundred and sixty-five pairs of adolescent and young adult twins registered with the South Korean Twin Registry completed the 7 scales of the Eysenck Personality Scales through a mail survey. Maximum likelihood twin correlations were computed and model-fitting analyses were conducted. Monozygotic twin correlations were consistently higher than twice the dizygotic twin correlations for all 7 scales, suggesting pervasive influences of nonadditive genetic effects on personality traits in the South Korean population. Model-fitting analyses indicated that genetic nonadditivity is particularly important for the variation of Impulsivity, Venturesomeness, Empathy, Lie, and Psychoticism. According to the best fitting models, nonadditive genetic effects ranged from 34 to 49% for these scales. For Neuroticism and Extraversion, models that included an additive genetic component fit better than those including a nonadditive genetic variance component.

Genetic and environmental influences on impulsivity: a meta-analysis of twin, family and adoption studies

A meta-analysis of twin, family and adoption studies was conducted to estimate the magnitude of genetic and environmental influences on impulsivity. The best fitting model for 41 key studies (58 independent samples from 14 month old infants to adults; N=27,147) included equal proportions of variance due to genetic (0.50) and non-shared environmental (0.50) influences, with genetic effects being both additive (0.38) and non-additive (0.12). Shared environmental effects were unimportant in explaining individual differences in impulsivity. Age, sex, and study design (twin vs. adoption) were all significant moderators of the magnitude of genetic and environmental influences on impulsivity. The relative contribution of genetic effects (broad sense heritability) and unique environmental effects were also found to be important throughout development from childhood to adulthood. Total genetic effects were found to be important for all ages, but appeared to be strongest in children. Analyses also demonstrated that genetic effects appeared to be stronger in males than in females. Method of assessment (laboratory tasks vs. questionnaires), however, was not a significant moderator of the genetic and environmental influences on impulsivity. These results provide a structured synthesis of existing behavior genetic studies on impulsivity by providing a clearer understanding of the relative genetic and environmental contributions in impulsive traits through various stages of development.

Decomposing group differences of latent means of ordered categorical variables within a genetic factor model

A genetic factor model is introduced for decomposition of group differences of the means of phenotypic behavior as well as individual differences when the research variables under consideration are ordered categorical. The model employs the general Genetic Factor Model proposed by Neale and Cardon (Methodology for genetic studies of twins and families, 1992) and, more specifically, the extension proposed by Dolan et al. (Behav Genet 22: 319-335, 1992) which enables decomposition of group differences of the means associated with genetic and environmental factors. Using a latent response variable (LRV) formulation (Muthén and Asparouhov, Latent variable analysis with categorical outcomes: multiple-group and growth modeling in Mplus. Mplus web notes: No. 4, Version 5, 2002), proportional differences of response categories between groups are modeled within the genetic factor model in terms of the distributional differences of latent response variables assumed to underlie the observed ordered categorical variables. Use of the proposed model is illustrated using a measure of conservatism in the data collected from the Australian Twin Registry.

The Behavioral Genetics of Personality Disorder

Behavioral genetics research has opened a new window on understanding personality disorder. The earliest studies were focused on establishing the relative contributions of genes and the environment in these disorders. Although these studies provided solid evidence of the importance of genetic and environmental influences on personality disorder and showed that all aspects of personality disorder are subject to genetic influence, heritability studies are limited because they are not helpful in explicating causal mechanisms. More recent research has focused on the relative contributions of the covariation of personality disorder diagnoses and traits, which allows one to examine etiological relationships. These developments are leading to major changes in ideas about what constitutes the environment and nature of the interplay between genes and environment. The present review examines major themes in this growing body of research in the context of current issues in the personality disorders.

Genetic and environmental components of adolescent adjustment and parental behavior: a multivariate analysis

Adolescent adjustment measures may be related to each other and to the social environment in various ways. Are these relationships similar in genetic and environmental sources of covariation, or different? A multivariate behavior-genetic analysis was made of 6 adjustment and 3 treatment composites from the study Nonshared Environment in Adolescent Development, using 674 same-sex adolescent sibling pairs aged 9-11. Cholesky decompositions of the total covariance matrix yielded additive and nonadditive genetic, and shared and nonshared environmental matrices. Factor analyses led to 3 factors for all but shared environment. The first 2 factors resembled Neuroticism and Extraversion factors typically found for personality; the third factor, parental monitoring and control, appeared to have different associations in different matrices.

Behavioral and molecular genetic contributions to a dimensional classification of personality disorder

This article examines the possible contribution of behavioral and molecular genetic research to the development of a dimensional classification of personality disorder. It is argued that the results of molecular studies are too preliminary to have immediate nosological significance. However, behavioral genetic methods could play a useful role in constructing a classification that reflects the genetic architecture of personality disorder. It is also argued that the best approach to constructing a valid classification would be to integrate behavioral genetic methods with the construct validation framework used in test construction. An integrative approach is proposed that seeks to combine constructs from alternative dimensional models. It is suggested that strong evidence of a four-dimensional structure to personality disorder provides a way to organize a preliminary model. An initial set of primary traits to define these secondary domains would then be compiled from existing models and refined using a combination of traditional psychometric analyses and behavioral genetic methods. It is concluded that an etiologically based classification is feasible for the DSM-V.

Assessing personality features and their relations with behavioral problems in adolescents: Tridimensional Personality Questionnaire and Junior Eysenck Personality Questionnaire

This study examines the applicability for adolescents of the Tridimensional Personality Questionnaire (TPQ), which was originally designed for adults, as compared to the Junior Eysenck Personality Questionnaire (JEPQ). The study also evaluates their inter-relationship and associations with various behavioral problems as reported by parents using the Child Behavior Checklist (CBCL). In a representative community sample of 905 adolescents, the results of internal consistency, test-retest reliability, and factor analysis showed that both the Harm Avoidance (HA) and the Novelty Seeking (NS) scales of the TPQ have sound construct validity, although the Reward Dependence (RD) scale has less so. The intercorrelation and factor analysis of the two questionnaires showed that the TPQ and the JEPQ are not simply alternative descriptions of the same construct of personality. In their associations with various behavioral problems, the scales of the TPQ are relatively more specifically associated with behavioral problems than the scales of the JEPQ. Our results provide empirical support for the applicability of the NS and the HA scales of the TPQ in adolescents, particularly in relation to behavioral problems.

Behavioural-genetic perspectives on personality function

In the wake of the recent announcements that the human genome has been mapped, efforts to identify the genetic loci underlying personality function will grow and intensify. Much research has already been done in this area, but it has for the most part been limited to classical biometrical approaches designed to determine if personality has a heritable basis. These so-called "heritability" studies estimate how much of the individual differences in personality are attributable to genetic differences among people. Molecular-genetic approaches, on the other hand, are designed to identify specific putative loci, but have yielded mixed results. The inconsistency in research findings can be attributed in part to the lack of sufficient numbers of genetic markers in the chromosomal regions of interest--a problem that the creation of a map of the human genome will help to rectify. This map and its inevitable refinements, however, can only advance the search for the genes for personality to a limited degree. Serious unresolved problems in the conceptualization and definition of personality and its dysfunction remain, which will hamper the search for personality genes.

Identifying Cloninger's temperament profiles as related to the early development of the metabolic cardiovascular syndrome in young men

Our aim in this study was to (1) identify naturally occurring temperament profiles in young adulthood by using Cloninger's temperament dimensions and (2) examine the relationship of these profiles with the coronary heart disease (CHD) risk factors of the metabolic cardiovascular syndrome (insulin resistance syndrome, IRS) measured during adolescence and young adulthood. A randomly selected sample of 190 healthy, young adult men was divided into 4 temperament groups by cluster analysis. Physiological parameters studied were serum insulin, high density lipoprotein cholesterol, triglycerides, systolic blood pressure, body-mass index, subscapular skinfold thickness, and the IRS factor. The results showed that a temperament profile characterized by a high level of persistence and reward dependence, an average level of novelty seeking, and a low level of harm avoidance was related to a high level of physiological CHD risk factors; in 3 study phases over a 6-year period, the subjects belonging to that cluster in adulthood were shown to have always belonged to the highest risk group in terms of the physiological risk factors in adolescence and young adulthood. The findings suggest that the temperament profile in question may predispose an individual to the development of the IRS and CHD.

Heritability of the big five personality dimensions and their facets: a twin study

The genetic and environmental etiology of the five-factor model of personality as measured by the revised NEO Personality Inventory (NEO-PI-R) was assessed using 123 pairs of identical twins and 127 pairs of fraternal twins. Broad genetic influence on the five dimensions of Neuroticism, Extraversion, Openness, Agreeableness, and Conscientiousness was estimated at 41%, 53%, 61%, 41%, and 44%, respectively. The facet scales also showed substantial heritability, although for several facets the genetic influence was largely nonadditive. The influence of the environment was consistent across all dimensions and facets. Shared environmental influences accounted for a negligible proportion of the variance in most scales, whereas nonshared environmental influences accounted for the majority of the environmental variance in all scales.

Genetic and environmental variation in Eysenck Personality Questionnaire scales measured on Australian adolescent twins

The Eysenck Personality Questionnaire was administered to 1400 Australian twin pairs aged 11 to 18, and the data were analyzed by a multivariate normal model using the software FISHER. For each scale, attempts were made to transform to normality, about a mean modeled separately for each sex as a quadratic function of age. Variances and covariances were estimated for each sex-zygosity group as a monotone function of age. Evidence for genetic sources of variation were assessed in part by fitting models which allowed for age-dependent, sex-specific, and correlated additive genetic factors, and age-dependent and sex-specific environmental factors, under the assumption that effects of environmental factors common to twin pairs are independent of zygosity. Evidence for genetic factors independent of age and sex was most compelling for Psychoticism and Neuroticism. For Extraversion, if genetic factors exist they would be mostly sex-specific and age-dependent. For the Lie scale there was evidence for, at most, a small component of genetic variation.

Perceived support and adjustment to stress in a general population sample of female twins

The stress-buffering effect of perceived support is explored in a large panel survey of adult female twins. The analysis begins by documenting a significant interaction between perceived support and acute stress in predicting DSM-III-R major depression. Various hypotheses are investigated to explain this interaction. These include the possibilities that the interaction is due to a stress-buffering effect of perceived support which is mediated by received support, that perceived support promotes either the increased use or the increased effectiveness of certain coping strategies, or that there is some underlying genetic factor that affects both the perception of support and adjustment to stress. No evidence was found for any of these hypotheses. The paper closes with a discussion of directions for future research aimed at explaining the interaction between perceived support and acute stress.

Multivariate genetic analysis of twin-family data on fears: Mx models

We describe the implementation of multivariate models of familial resemblance with the Mx package. The structural equation models allow for the effects of assortative mating, additive and dominant genes, common and specific environment, and both genetic and cultural transmission between generations. Two approaches are compared: a correlational one based on Fulker and a factor model described by Phillips and Fulker. Both are illustrated by application to published data on social fears and fear of leadership measured in monozygotic and dizygotic twins and their parents. In the example data, genetic dominance yields a more parsimonious explanation of the data than does cultural transmission, although neither is needed to obtain a good fit to the data. A model of reduced genetic correlation between generations also fits the data but has inherent limitations in this sample. Extensions to sex-limitation and more complex models are discussed.

Multiple Regression With Data Collected From Relatives: Testing Assumptions of the Model

Multiple regression is a causal model of the relationship between sets of independent (X) and dependent (Y) variables. This model is extended to cover data collected from relatives, where the observations are not independent. If correct, the model permits appropriate statistical tests of regression coefficients in data collected from relatives. Across relative covariances, particularly across the independent and dependent variables may reject the basic regression model. Further extensions of the model are developed that permit tests of several assumptions implicit in multiple regression: (a) the assignment of variables as dependent or independent; (b) the relationship between X and Y variables is not due to some latent variable which causes variation in both; and (c) there is no reciprocal interaction between the X and the Y variables. Discrimination between these alternatives is especially strong if data are collected from more than one class of relative, which differ in their X and Y variable covariance structure. Data on Eysenck Extraversion, Neuroticism and CESD depression collected from twins are used as an illustrative example.

Personality is indeterminate

The so-called unique environmental factor in behaviour genetics research, the longitudinal instability of personality, and the unpredictability of human creativity are all manifestations of the same process. Thus a scientific explanation of any one of them should account for them all. That process, it is proposed, is the inherently indeterminate global dynamics of the human brain. The clear implication is that all social sciences have inherently indeterminate phenomena as their subject matter. Predictions of the results of an appropriately designed psychometric study based on this hypothesis are offered.

Brain, environment, heredity, and personality

Behavior genetics research, committed to a model of the origins of personality and intellectual development restricted to heredity and environment, consistently generates evidence for two types of environmental influences. One of these, termed the between-family or shared environment, creates no conceptual problems. The other, termed the nonshared or within-family or unique environment, does. The other, termed the nonshared or within-family or unique environment, does. The latter accounts for a substantial portion of the variance in personality and intellect, it must be unique to each individual, and its origin has not been determined. It is contended here that the brain itself, as an inherently indeterminate dynamic system, is the source of this unresolved developmental variability.

Testing hypotheses about direction of causation using cross-sectional family data

We review the conditions under which cross-sectional family data (e.g., data on twin pairs or adoptees and their adoptive and biological relatives) are informative about direction of causation. When two correlated traits have rather different modes of inheritance (e.g., family resemblance is determined largely by family background for one trait and by genetic factors for the other trait), cross-sectional family data will allow tests of strong unidirectional causal hypotheses (A and B are correlated "because of the causal influence of A on B" versus "because of the causal influence of B on A") and, under some conditions, also of the hypothesis of reciprocal causation. Possible sources of errors of inference are considered. Power analyses are reported which suggest that multiple indicator variables will be needed to ensure adequate power of rejecting false models in the presence of realistic levels of measurement error. These methods may prove useful in cases where conventional methods to establish causality, by intervention, by prospective study, or by measurement of instrumental variables, are unfeasible economically, ethically or practically.

Decomposition of multivariate phenotypic means in multigroup genetic covariance structure analysis

Observed differences in phenotypic means between groups such as parents and their offspring or male and female twins can be decomposed into genetic and environmental components. The decomposition is based on the assumption that the difference in phenotypic means is due to a difference in the location of the normal genetic and environmental distributions underlying the phenotypic individual differences. Differences between the groups in variance can be accommodated insofar as they are due to differences in unique variance or can be modeled using a scale parameter. The decomposition may be carried out in the standard analysis of genetic covariance structure using, for instance, LISREL. Illustrations are given using simulated data and twin data relating to blood pressure. Other possible applications are mentioned.

Religion and education as mediators of attitudes: a multivariate analysis

The transmission of social attitudes has been investigated as a possible model of cultural inheritance in a sample of 3810 twin pairs from the Australian National Health and Medical Research Twin Registry. Six social attitude factors were identified and univariate genetic models fitted to scores on each factor. A joint multivariate genetic analysis of the six attitude factors, church attendance, and education indicated that the attitudes were correlated--the same genes and shared environments influenced more than one attitude factor. A current controversy regarding social attitudes is whether the significant loadings on this shared environmental component represent true cultural influences or are actually the genetic consequences of phenotypic assortative mating for church attendance and educational attainment (Martin et al., 1986). In our data, church attendance is almost entirely due to the impact of the shared environment. The large shared environmental component on church attendance also accounts for a substantial part of the family resemblance in social attitudes, suggesting that not all of the apparent cultural effects found in earlier studies can be ascribed to the genetic effects of assortative mating. However, church attendance and education do not completely account for the cultural component. Therefore, effects in addition to church attendance, education, and assortative mating for church attendance and education must be involved in the cultural component of the inheritance of attitudes.

Further contribution to the conceptual validity of the unified biosocial model of personality: US and Yugoslav data

In this study, the conceptual validity of the unified model of personality, postulated by Cloninger (1987) and measured by the Tridimensional Personality Questionnaire (TPQ), is tested in diverse Yugoslav and American societies. The issue of cross-cultural sensitivity of personality studies and the methodology that minimizes distortions and alternative explanations are discussed in detail. Similar personality structures were observed in the Yugoslav and US samples. Differences in novelty seeking (NS, attributed to age differences between the two samples) and harm avoidance (HA, possibly due to long-standing socioeconomic instability in Yugoslavia) are consistent with the unified biosocial theory of personality. Also, the TPQ was found to be psychometrically sound and valid for further research, although some revision in the reward dependence (RD) scale is warranted.