Juko Ando

Is the genetic structure of human personality universal? A cross-cultural twin study from North America, Europe, and Asia.

This study examined whether universality of the 5-factor model (FFM) of personality operationalized by the Revised NEO Personality Inventory is due to genetic influences that are invariant across diverse nations. Factor analyses were conducted on matrices of phenotypic, genetic, and environmental correlations estimated in a sample of 1,209 monozygotic and 701 dizygotic twin pairs from Canada, Germany, and Japan. Five genetic and environmental factors were extracted for each sample. High congruence coefficients were observed when phenotypic, genetic, and environmental factors were compared in each sample as well as when each factor was compared across samples. These results suggest that the FFM has a solid biological basis and may represent a common heritage of the human species.

Genetic structure of spatial and verbal working memory

Working memory (WM) encompasses both short-term memory (storage) and executive functions that play an essential role in all forms of cognition. In this study, the genetic structure of storage and executive functions engaged in both a spatial and verbal WM span task is investigated using a twin sample. The sample consists of 143 monozygotic (MZ) and 93 dizygotic (DZ) Japanese twin pairs, ages 16 to 29 years. In 155 (87 MZ, 62 DZ) of these pairs, cognitive ability scores from the Kyodai Japanese IQ test are also obtained. The phenotypic relationship between WM and cognitive ability is confirmed (r = 0.26−0.44). Individual differences in WM storage and executive functions are found to be significantly influenced by genes, with heritability estimates all moderately high (43%–49%), and estimates for cognitive ability comparable to previous studies (65%). A large part of the genetic variance in storage and executive functions in both spatial and verbal modalities is due to a common genetic factor that accounts for 11% to 43% of the variance. In the reduced sample, this common genetic factor accounts for 64% and 26% of the variance in spatial and verbal cognitive ability, respectively. Additional genetic variance in WM (7%–30%) is due to modality specific factors (spatial and verbal) and a storage specific factor that may be particularly important for the verbal modality. None of the variance in cognitive ability is accounted for by the modality and storage genetic factors, suggesting these may be specific to WM.

A general factor of personality from multitrait-multimethod data and cross-national twins

In three studies, a General Factor of Personality (GFP) was found to occupy the apex of the hierarchical structure. In Study 1, a GFP emerged independent of method variance and accounted for 54% of the reliable variance in a multitrait-multimethod assessment of 391 Italian high school students that used self-, teacher-, and parent-ratings on the Big Five Questionnaire - Children. In Study 2, a GFP was found in the seven dimensions of Cloningers Temperament and Character Inventory as well as the Big Five of the NEO PI-R, with the GFPtci correlating r = .72 with the GFPneo. These results indicate that the GFP is practically the same in both test batteries, and its existence does not depend on being extracted using the Big Five model. The GFP accounted for 22% of the total variance in these trait measures, which were assessed in 651 pairs of 14- to 30-year-old Japanese twins. In Study 3, a GFP accounted for 32% of the total variance in nine scales derived from the NEO PI-R, the Humor Styles Questionnaire, and the Trait Emotional Intelligence Questionnaire assessed in 386 pairs of 18- to 74-year-old Canadian and U.S. twins. The GFP was found to be 50% heritable with high scores indicating openness, conscientiousness, sociability, agreeableness, emotional stability, good humor and emotional intelligence. The possible evolutionary origins of the GFP are discussed.

GENETIC AND ENVIRONMENTAL STRUCTURE OF CLONINGER'S TEMPERAMENT AND CHARACTER DIMENSIONS

The multivariate genetic and environmental structure of Cloningers Temperament and Character Inventory (TCI) was investigated in a sample of 617 pairs of adolescent and young adult twins from Japan. Additive genetic factors accounted for 22% to 49% of the variability on all TCI temperament scales. Although the theory predicts lower heritability for the character scales, all character subscales had a substantial genetic contribution, and nonshared environmental influences accounted for the remainder. Multivariate genetic analyses showed that several subscales used to define one dimension shared a common genetic basis with subscales defining others. Using the degree of shared genetic influence as the basis to rearrange the TCI subscales into new dimensions, it was possible to create genetically independent scales. The implications for personality measurement, theory, and molecular genetic research are discussed.

Substance and artifact in the higher-order factors of the Big Five.

J. M. Digman (1997) proposed that the Big Five personality traits showed a higher-order structure with 2 factors he labeled alpha and beta. These factors have been alternatively interpreted as heritable components of personality or as artifacts of evaluative bias. Using structural equation modeling, the authors reanalyzed data from a cross-national twin study and from American cross-observer studies and analyzed new multimethod data from a German twin study. In all analyses, artifact models outperformed substance models by root-mean-square error of approximation criteria, but models combining both artifact and substance were slightly better. These findings suggest that the search for the biological basis of personality traits may be more profitably focused on the 5 factors themselves and their specific facets, especially in monomethod studies.

The genetic structure of Cloninger's seven-factor model of temperament and character in a Japanese sample

Theoretical assumptions regarding the genetic and environmental structure of personality proposed in Cloningers seven-factor model of temperament and character were verified in a Japanese sample by using the twin method. The Temperament and Character Inventory (TCI) was administered to 296 twin pairs ranging in age from 14 to 28 years old. Among four temperament dimensions (novelty seeking [NS], harm avoidance [HA], reward dependence [RD], and persistence [PS]), HA and PS showed significant additive genetic contributions and no shared environmental effect, supporting the original theoretical assumption. NS and RD could be explained by either genetic or shared environmental factors with nonshared environment. All three character dimensions (cooperativeness [CO], self-directedness [SD], and self-transcendence [ST]) could be explained exclusively by additive contributions and no shared environmental effect. Multivariate genetic analysis indicated that there were no significant associations between NS, HA, and RD, as the theory predicts, and the genetic components of PS, SD, and CO were derived from those of the temperament dimensions. The fourth genetic component, which had a substantial load specifically on ST and overlapped with PS, was identified. Although most of the nonshared environmental effects were trait-specific, the phenotypic correlation between NS and HA could be explained by nonshared environmental overlap.

Covariance Structure of Neuroticism and Agreeableness: A Twin and Molecular Genetic Analysis of the Role of the Serotonin Transporter Gene

The Revised NEO Personality Inventory domains of Neuroticism and Agreeableness are considered factorially distinct despite several intercorrelations between these domains. The genetic correlation, an index of the degree to which these intercorrelations are caused by genetic influences, was estimated using data from 913 monozygotic and 562 dizygotic volunteer twin pairs from Canada, Germany, and Japan. The serotonin transporter gene, 5-HTTLPR, was assayed in a sample of 388 nontwin sibling pairs from the United States to determine the contribution of the serotonin transporter locus to the covariation between the Neuroticism and Agreeableness scales. In all four samples, genetic influences contributed to the covariance of Neuroticism and Agreeableness, with the serotonin transporter gene accounting for 10% of the relationship between these domains.

Dimensions of temperament as vulnerability factors in depression

In order to evaluate the hypothesis that one set of genetic risk factors may be common to disorders and dimensions of temperament, whereas environmental risk factors are disorder specific, we have conducted a genetic analysis of dimensions of temperament and symptoms of depression in about 201 pairs of monozygotic and dizygotic twins. Dimensions of temperament associated with novelty seeking, harm avoidance, reward dependence, and persistence were measured by using the Temperament and Character Instruments developed by Cloninger, and depressive symptoms were measured using the Hospital Anxiety and Depression Scale. Differences among individuals on these measures can be explained by differences in their genes and in their environmental experiences. There are no differences between the sexes in gene action affecting temperament. Each dimension of temperament is genetically dependent, and genetic variations in symptoms of depression are largely dependent on the same factors that affect the temperament. Temperament is closely associated with vulnerability to depressive symptoms.

Genetic influences on the difference in variability of height, weight and body mass index between Caucasian and East Asian adolescent twins

Objective:Twin studies are useful for investigating the causes of trait variation between as well as within a population. The goals of the present study were two-fold: First, we aimed to compare the total phenotypic, genetic and environmental variances of height, weight and BMI between Caucasians and East Asians using twins. Secondly, we intended to estimate the extent to which genetic and environmental factors contribute to differences in variability of height, weight and BMI between Caucasians and East Asians.Design:Height and weight data from 3735 Caucasian and 1584 East Asian twin pairs (age: 13–15 years) from Australia, China, Finland, Japan, the Netherlands, South Korea, Taiwan and the United States were used for analyses. Maximum likelihood twin correlations and variance components model-fitting analyses were conducted to fulfill the goals of the present study.Results:The absolute genetic variances for height, weight and BMI were consistently greater in Caucasians than in East Asians with corresponding differences in total variances for all three body measures. In all 80 to 100% of the differences in total variances of height, weight and BMI between the two population groups were associated with genetic differences.Conclusion:Height, weight and BMI were more variable in Caucasian than in East Asian adolescents. Genetic variances for these three body measures were also larger in Caucasians than in East Asians. Variance components model-fitting analyses indicated that genetic factors contributed to the difference in variability of height, weight and BMI between the two population groups. Association studies for these body measures should take account of our findings of differences in genetic variances between the two population groups.

Genetic and Environmental Etiology of Effortful Control

We examined whether effortful control (EC), a temperament proposed by Rothbart and Bates (1998), has genetically coherent structure. A self-report measure of EC was administered to 450 Japanese twins (151 males and 299 females, ages 17 to 32 years) including 152 monozygotic and 73 dizygotic pairs. Univariate genetic analysis revealed that AE model fit best for the total EC as well as its subscales. The heritability estimate for total EC was 49%, and the estimates for subscales ranged between 32% and 45%. Multivariate genetic analysis revealed that the subscales of EC were genetically correlated to a high degree and environmentally correlated to a moderate degree. These results suggest that EC has substantial genetic basis and genetically coherent structure, supporting the validity of the construct. The implications to molecular genetic study and study of psychopathology were discussed.