Meta-analysis of genome-wide association studies for personality

Identification of genetic loci shared between schizophrenia and the Big Five personality traits

Schizophrenia is associated with differences in personality traits, and recent studies suggest that personality traits and schizophrenia share a genetic basis. Here we aimed to identify specific genetic loci shared between schizophrenia and the Big Five personality traits using a Bayesian statistical framework. Using summary statistics from genome-wide association studies (GWAS) on personality traits in the 23andMe cohort (n = 59,225) and schizophrenia in the Psychiatric Genomics Consortium cohort (n = 82,315), we evaluated overlap in common genetic variants. The Big Five personality traits neuroticism, extraversion, openness, agreeableness and conscientiousness were measured using a web implementation of the Big Five Inventory. Applying the conditional false discovery rate approach, we increased discovery of genetic loci and identified two loci shared between neuroticism and schizophrenia and six loci shared between openness and schizophrenia. The study provides new insights into the relationship between personality traits and schizophrenia by highlighting genetic loci involved in their common genetic etiology.

LD Hub: a centralized database and web interface to perform LD score regression that maximizes the potential of summary level GWAS data for SNP heritability and genetic correlation analysis

MOTIVATION

LD score regression is a reliable and efficient method of using genome-wide association study (GWAS) summary-level results data to estimate the SNP heritability of complex traits and diseases, partition this heritability into functional categories, and estimate the genetic correlation between different phenotypes. Because the method relies on summary level results data, LD score regression is computationally tractable even for very large sample sizes. However, publicly available GWAS summary-level data are typically stored in different databases and have different formats, making it difficult to apply LD score regression to estimate genetic correlations across many different traits simultaneously.

RESULTS

In this manuscript, we describe LD Hub - a centralized database of summary-level GWAS results for 173 diseases/traits from different publicly available resources/consortia and a web interface that automates the LD score regression analysis pipeline. To demonstrate functionality and validate our software, we replicated previously reported LD score regression analyses of 49 traits/diseases using LD Hub; and estimated SNP heritability and the genetic correlation across the different phenotypes. We also present new results obtained by uploading a recent atopic dermatitis GWAS meta-analysis to examine the genetic correlation between the condition and other potentially related traits. In response to the growing availability of publicly accessible GWAS summary-level results data, our database and the accompanying web interface will ensure maximal uptake of the LD score regression methodology, provide a useful database for the public dissemination of GWAS results, and provide a method for easily screening hundreds of traits for overlapping genetic aetiologies.

AVAILABILITY AND IMPLEMENTATION

The web interface and instructions for using LD Hub are available at http://ldsc.broadinstitute.org/ CONTACT: jie.zheng@bristol.ac.ukSupplementary information: Supplementary data are available at Bioinformatics online.

Sensation seeking and impulsive traits as personality endophenotypes for antisocial behavior: Evidence from two independent samples

Sensation seeking and impulsivity are personality traits that are correlated with risk for antisocial behavior (ASB). This paper uses two independent samples of twins to (a) test the extent to which sensation seeking and impulsivity statistically mediate genetic influence on ASB, and (b) compare this to genetic influences accounted for by other personality traits. In Sample 1, delinquent behavior, as well as impulsivity, sensation seeking and Big Five personality traits, were measured in adolescent twins from the Texas Twin Project. In Sample 2, adult twins from the Australian Twin Registry responded to questionnaires that assessed individual differences in Eysenck's and Cloninger's personality dimensions, and a structured telephone interview that asked participants to retrospectively report DSM-defined symptoms of conduct disorder. Bivariate quantitative genetic models were used to identify genetic overlap between personality traits and ASB. Across both samples, novelty/sensation seeking and impulsive traits accounted for larger portions of genetic variance in ASB than other personality traits. We discuss whether sensation seeking and impulsive personality are causal endophenotypes for ASB, or merely index genetic liability for ASB.

Genome-wide analyses for personality traits identify six genomic loci and show correlations with psychiatric disorders

Personality is influenced by genetic and environmental factors and associated with mental health. However, the underlying genetic determinants are largely unknown. We identified six genetic loci, including five novel loci, significantly associated with personality traits in a meta-analysis of genome-wide association studies (N = 123,132-260,861). Of these genome-wide significant loci, extraversion was associated with variants in WSCD2 and near PCDH15, and neuroticism with variants on chromosome 8p23.1 and in L3MBTL2. We performed a principal component analysis to extract major dimensions underlying genetic variations among five personality traits and six psychiatric disorders (N = 5,422-18,759). The first genetic dimension separated personality traits and psychiatric disorders, except that neuroticism and openness to experience were clustered with the disorders. High genetic correlations were found between extraversion and attention-deficit-hyperactivity disorder (ADHD) and between openness and schizophrenia and bipolar disorder. The second genetic dimension was closely aligned with extraversion-introversion and grouped neuroticism with internalizing psychopathology (e.g., depression or anxiety).

A behavioral genetic analysis of callous-unemotional traits and Big Five personality in adolescence

Callous-unemotional (CU) traits, such as lacking empathy and emotional insensitivity, predict the onset, severity, and persistence of antisocial behavior. CU traits are heritable, and genetic influences on CU traits contribute to antisocial behavior. This study examines genetic overlap between CU traits and general domains of personality. We measured CU traits using the Inventory of Callous-Unemotional Traits (ICU) and Big Five personality using the Big Five Inventory in a sample of adolescent twins from the Texas Twin Project. Genetic influences on the Big Five personality dimensions could account for the entirety of genetic influences on CU traits. Item Response Theory results indicate that the Inventory of Callous and Unemotional Traits is better at detecting clinically relevant personality variation at lower extremes of personality trait continua, particularly low agreeableness and low conscientiousness. The proximate biological mechanisms that mediate genetic liabilities for CU traits remain an open question. The results of the current study suggest that understanding the development of normal personality may inform understanding of the genetic underpinnings of callous and unemotional behavior.

SNP-based heritability estimates of the personality dimensions and polygenic prediction of both neuroticism and major depression: findings from CONVERGE

Biometrical genetic studies suggest that the personality dimensions, including neuroticism, are moderately heritable (~0.4 to 0.6). Quantitative analyses that aggregate the effects of many common variants have recently further informed genetic research on European samples. However, there has been limited research to date on non-European populations. This study examined the personality dimensions in a large sample of Han Chinese descent (N=10 064) from the China, Oxford, and VCU Experimental Research on Genetic Epidemiology study, aimed at identifying genetic risk factors for recurrent major depression among a rigorously ascertained cohort. Heritability of neuroticism as measured by the Eysenck Personality Questionnaire (EPQ) was estimated to be low but statistically significant at 10% (s.e.=0.03, P=0.0001). In addition to EPQ, neuroticism based on a three-factor model, data for the Big Five (BF) personality dimensions (neuroticism, openness, conscientiousness, extraversion and agreeableness) measured by the Big Five Inventory were available for controls (n=5596). Heritability estimates of the BF were not statistically significant despite high power (>0.85) to detect heritabilities of 0.10. Polygenic risk scores constructed by best linear unbiased prediction weights applied to split-half samples failed to significantly predict any of the personality traits, but polygenic risk for neuroticism, calculated with LDpred and based on predictive variants previously identified from European populations (N=171 911), significantly predicted major depressive disorder case-control status (P=0.0004) after false discovery rate correction. The scores also significantly predicted EPQ neuroticism (P=6.3 × 10-6). Factor analytic results of the measures indicated that any differences in heritabilities across samples may be due to genetic variation or variation in haplotype structure between samples, rather than measurement non-invariance. Findings demonstrate that neuroticism can be significantly predicted across ancestry, and highlight the importance of studying polygenic contributions to personality in non-European populations.

Breastfeeding and Adult Personality

Five Factor Model (FFM) personality traits are implicated in long-term health-risk behaviors and outcomes. Less research has addressed how early-life experiences are associated with individual differences in these traits in adulthood. We examine whether having been breastfed is associated with adult personality and well-being in the National Longitudinal Study of Adolescent to Adult Health. At Wave 1, caregivers reported whether the target child had been breastfed. At Wave 4, participants (N=13,113; 53% female; M_age=28.98) completed measures of psychological functioning. We tested for mean-level differences in the traits by breastfeeding status (yes/no) and by the duration of breastfeeding, controlling for basic demographic factors and early-life factors that could confound the breastfeeding-personality association (e.g., mother education). Participants who had been breastfed scored lower in neuroticism, anxiety, and hostility and higher in openness and optimism than those not breastfed. A curvilinear relation suggested that neuroticism was lowest for those breastfed for 9-12 months and highest for those either breastfed for >24 months or exclusively bottle-fed. Breastfeeding was unrelated to conscientiousness or state psychological functioning. This research suggests long-term psychological benefits to breastfeeding and indicates that early life experiences are associated with traits that are consequential for adult health.

Opportunities and challenges of big data for the social sciences: The case of genomic data

In this paper, we draw attention to one unique and valuable source of big data, genomic data, by demonstrating the opportunities they provide to social scientists. We discuss different types of large-scale genomic data and recent advances in statistical methods and computational infrastructure used to address challenges in managing and analyzing such data. We highlight how these data and methods can be used to benefit social science research.

Personality Polygenes, Positive Affect, and Life Satisfaction

Approximately half of the variation in wellbeing measures overlaps with variation in personality traits. Studies of non-human primate pedigrees and human twins suggest that this is due to common genetic influences. We tested whether personality polygenic scores for the NEO Five-Factor Inventory (NEO-FFI) domains and for item response theory (IRT) derived extraversion and neuroticism scores predict variance in wellbeing measures. Polygenic scores were based on published genome-wide association (GWA) results in over 17,000 individuals for the NEO-FFI and in over 63,000 for the IRT extraversion and neuroticism traits. The NEO-FFI polygenic scores were used to predict life satisfaction in 7 cohorts, positive affect in 12 cohorts, and general wellbeing in 1 cohort (maximal N = 46,508). Meta-analysis of these results showed no significant association between NEO-FFI personality polygenic scores and the wellbeing measures. IRT extraversion and neuroticism polygenic scores were used to predict life satisfaction and positive affect in almost 37,000 individuals from UK Biobank. Significant positive associations (effect sizes <0.05%) were observed between the extraversion polygenic score and wellbeing measures, and a negative association was observed between the polygenic neuroticism score and life satisfaction. Furthermore, using GWA data, genetic correlations of −0.49 and −0.55 were estimated between neuroticism with life satisfaction and positive affect, respectively. The moderate genetic correlation between neuroticism and wellbeing is in line with twin research showing that genetic influences on wellbeing are also shared with other independent personality domains.

Predicting gene targets from integrative analyses of summary data from GWAS and eQTL studies for 28 human complex traits

Genome-wide association studies (GWAS) have identified hundreds of genetic variants associated with complex traits and diseases. However, elucidating the causal genes underlying GWAS hits remains challenging. We applied the summary data-based Mendelian randomization (SMR) method to 28 GWAS summary datasets to identify genes whose expression levels were associated with traits and diseases due to pleiotropy or causality (the expression level of a gene and the trait are affected by the same causal variant at a locus). We identified 71 genes, of which 17 are novel associations (no GWAS hit within 1 Mb distance of the genes). We integrated all the results in an online database ( http://www.cnsgenomics/shiny/SMRdb/ ), providing important resources to prioritize genes for further follow-up, for example in functional studies.

Towards More Rigorous Personality Trait–Outcome Research

Much of personality research attempts to identify causal links between personality traits and various types of outcomes. I argue that causal interpretations require traits to be seen as existentially and holistically real and the associations to be independent of specific ways of operationalizing the traits. Among other things, this means that, to the extents that causality is to be ascribed to such holistic traits, items and facets of those traits should be similarly associated with specific outcomes, except for variability in the degrees to which they reflect the traits (i.e. factor loadings). I argue that, before drawing causal inferences about personality trait–outcome associations, the presence of this condition should be routinely tested by, for example, systematically comparing the outcome associations of individual items or facets, or sampling different indicators for measuring the same purported traits. Existing evidence suggests that observed associations between personality traits and outcomes at least sometimes depend on which particular items or facets have been included in trait operationalizations, calling trait–level causal interpretations into question. However, this has rarely been considered in the literature. I argue that when outcome associations are specific to facets, they should not be generalized to traits. Furthermore, when the associations are specific to particular items, they should not even be generalized to facets. Copyright © 2016 European Association of Personality Psychology

Single nucleotide polymorphisms in the REG-CTNNA2 region of chromosome 2 and NEIL3 associated with impulsivity in a Native American sample

Impulsivity is a multi-faceted construct that, while characterized by a set of correlated dimensions, is centered around a core definition that involves acting suddenly in an unplanned manner without consideration for the consequences of such behavior. Several psychiatric disorders include impulsivity as a criterion, and thus it has been suggested that it may link a number of different behavioral disorders, including substance abuse. Native Americans (NA) experience some of the highest rates of substance abuse of all the US ethnic groups. The described analyses used data from a low-coverage whole genome sequence scan to conduct a genome-wide association study (GWAS) of an impulsivity phenotype in an American Indian community sample (n = 658). Demographic and clinical information were obtained using a semi-structured interview. Impulsivity was assessed using a scale derived from the Maudsley personality inventory that combines both novelty seeking and lack of planning items. The impulsivity score was tested for association with each variant adjusted for demographic variables, and corrected for ancestry and kinship, using emmax. Simulations were conducted to calculate empirical P-values. Genome-wide significant findings were observed for a variant 50-kb upstream from catenin cadherin-associated protein, alpha 2 (CTNNA2), a neuronal-specific catenin, in the REG gene cluster. A meta-analysis of GWAS had previously identified common variants in CTNNA2 as being associated with excitement seeking. A second locus upstream of nei endonuclease VIII-like 3 (NEIL3) on chromosome 4 also achieved genome-wide significance. The association between sequence variants in these regions suggests their potential roles in the genetic regulation of this phenotype in this population.

Mechanisms of the placebo effect in pain and psychiatric disorders

Placebo effect research over the past 15 years has improved our understanding of how placebo treatments reduce patient symptoms. The expectation of symptom improvement is the primary factor underlying the placebo effect. Such expectations are shaped by past experiences, contextual cues and biological traits, which ultimately modulate one's degree of response to a placebo. The body of evidence that describes the physiology of the placebo effect has been derived from mechanistic studies primarily restricted to the setting of pain. Imaging findings support the role of endogenous opioid and dopaminergic networks in placebo analgesia in both healthy patients as well as patients with painful medical conditions. In patients with psychiatric illnesses such as anxiety disorders or depression, a vast overlap in neurological changes is observed in drug responders and placebo responders supporting the role of serotonergic networks in placebo response. Molecular techniques have been relatively underutilized in understanding the placebo effect until recently. We present an overview of the placebo responder phenotypes and genetic markers that have been associated with the placebo effect in pain, schizophrenia, anxiety disorders and depression.

BDNF Val66Met genotype and neuroticism predict life stress: A longitudinal study from childhood to adulthood

The brain-derived neurotrophic factor gene (BDNF) Val66Met polymorphism and life stress have been associated with negative emotionality (e.g., neuroticism), but relevant evidence is far from unequivocal. Possible confounding factors include the type and timing of stressful events measured, such as childhood adversity vs. recent stressful events, and variable gene × environment interactions. The aim of this study was to longitudinally assess the BDNF Val66Met polymorphism and environment interaction effect on neuroticism in a population representative sample, depending upon the type of stress, gender and family relations. In the original older cohort of the Estonian Children Personality Behavior and Health Study (ECPBHS, n=593), neuroticism was measured at age 15 (parental assessment), 18 and 25 (self-assessments). Childhood stress was reported at age 15, quality of family relations was measured at age 18, and recent stressful life events at age 25. The BDNF Val66Met polymorphism interacted with recent stressful life events, but not with childhood adversities, to impact neuroticism. Interestingly, in female participants, neuroticism at age 18 predicted future stressful life events dependent upon genotype: individuals with Val/Val genotype and high neuroticism experienced higher, but Met-allele carriers with high neuroticism lower stress exposure at age 25. Similar tendencies were observed using parental assessments at age 15. The protective effect of Met-allele in the high stress exposure group could result from better early family environment. In conclusion, we herewith provide further evidence for a role of BDNF gene variance contributing to plasticity in response to environmental demands.

Meta-analysis of Genome-Wide Association Studies for Extraversion: Findings from the Genetics of Personality Consortium

Extraversion is a relatively stable and heritable personality trait associated with numerous psychosocial, lifestyle and health outcomes. Despite its substantial heritability, no genetic variants have been detected in previous genome-wide association (GWA) studies, which may be due to relatively small sample sizes of those studies. Here, we report on a large meta-analysis of GWA studies for extraversion in 63,030 subjects in 29 cohorts. Extraversion item data from multiple personality inventories were harmonized across inventories and cohorts. No genome-wide significant associations were found at the single nucleotide polymorphism (SNP) level but there was one significant hit at the gene level for a long non-coding RNA site (LOC101928162). Genome-wide complex trait analysis in two large cohorts showed that the additive variance explained by common SNPs was not significantly different from zero, but polygenic risk scores, weighted using linkage information, significantly predicted extraversion scores in an independent cohort. These results show that extraversion is a highly polygenic personality trait, with an architecture possibly different from other complex human traits, including other personality traits. Future studies are required to further determine which genetic variants, by what modes of gene action, constitute the heritable nature of extraversion.

The Genetics of Stress-Related Disorders: PTSD, Depression, and Anxiety Disorders

Research into the causes of psychopathology has largely focused on two broad etiologic factors: genetic vulnerability and environmental stressors. An important role for familial/heritable factors in the etiology of a broad range of psychiatric disorders was established well before the modern era of genomic research. This review focuses on the genetic basis of three disorder categories-posttraumatic stress disorder (PTSD), major depressive disorder (MDD), and the anxiety disorders-for which environmental stressors and stress responses are understood to be central to pathogenesis. Each of these disorders aggregates in families and is moderately heritable. More recently, molecular genetic approaches, including genome-wide studies of genetic variation, have been applied to identify specific risk variants. In this review, I summarize evidence for genetic contributions to PTSD, MDD, and the anxiety disorders including genetic epidemiology, the role of common genetic variation, the role of rare and structural variation, and the role of gene-environment interaction. Available data suggest that stress-related disorders are highly complex and polygenic and, despite substantial progress in other areas of psychiatric genetics, few risk loci have been identified for these disorders. Progress in this area will likely require analysis of much larger sample sizes than have been reported to date. The phenotypic complexity and genetic overlap among these disorders present further challenges. The review concludes with a discussion of prospects for clinical translation of genetic findings and future directions for research.

Romantic Relationship Satisfaction Moderates the Etiology of Adult Personality

The heritability of major normative domains of personality is well-established, with approximately half the proportion of variance attributed to genetic differences. In the current study, we examine the possibility of gene × environment interaction (G×E) for adult personality using the environmental context of intimate romantic relationship functioning. Personality and relationship satisfaction are significantly correlated phenotypically, but to date no research has examined how the genetic and environmental components of variance for personality differ as a function of romantic relationship satisfaction. Given the importance of personality for myriad outcomes from work productivity to psychopathology, it is vital to identify variables present in adulthood that may affect the etiology of personality. In the current study, quantitative models of G×E were used to determine whether the genetic and environmental influences on personality differ as a function of relationship satisfaction. We drew from a sample of now-adult twins followed longitudinally from adolescence through age 29. All participants completed the Multidimensional Personality Questionnaire (MPQ) and an abbreviated version of the Dyadic Adjustment Scale. Biometric moderation was found for eight of the eleven MPQ scales examined: well-being, social potency, negative emotionality, alienation, aggression, constraint, traditionalism, and absorption. The pattern of findings differed, suggesting that the ways in which relationship quality moderates the etiology of personality may depend on the personality trait.

The genetics of loneliness: linking evolutionary theory to genome-wide genetics, epigenetics, and social science

As a complex trait, loneliness is likely to be influenced by the interplay of numerous genetic and environmental factors. Studies in behavioral genetics indicate that loneliness has a sizable degree of heritability. Candidate-gene and gene-expression studies have pointed to several genes related to neurotransmitters and the immune system. The notion that these genes are related to loneliness is compatible with the basic tenets of the evolutionary theory of loneliness. Research on gene-environment interactions indicates that social-environmental factors (e.g., low social support) may have a more pronounced effect and lead to higher levels of loneliness if individuals carry the sensitive variant of these candidate genes. Currently, there is no extant research on loneliness based on genome-wide association studies, gene-environment-interaction studies, or studies in epigenetics. Such studies would allow researchers to identify networks of genes that contribute to loneliness. The contribution of genetics to loneliness research will become stronger when genome-wide genetics and epigenetics are integrated and used along with well-established methods in psychology to analyze the complex process of gene-environment interplay.

Personality traits across cultures

Current questions in the study of personality traits across cultures include (a) the universality versus cultural uniqueness of trait structure, (b) cultural differences in trait levels, (c) the consistency and validity of traits and their measures across cultures, and (d) the evolutionary, ecological, and cultural contexts of personality. Although the Five Factor Model (FFM) of personality continues to find cross-cultural support, new research suggests that the model may be difficult to replicate in less educated or preliterate groups and that indigenous social-relational concepts may be distinguishable from the FFM in some cultures. In lexical studies, two or three broad dimensions may replicate better across cultures than alternative models. Substantial evidence suggests that mean trait profiles of cultures may be reasonably accurate. Nonetheless, research on response styles and measurement invariance raises questions about cross-cultural trait comparisons. Findings regarding cultural differences in trait-related consistency and validity are mixed. Researchers are offering innovative theory and research on the evolutionary, ecological, and cultural contexts of personality.

Fifty psychological and psychiatric terms to avoid: a list of inaccurate, misleading, misused, ambiguous, and logically confused words and phrases

The goal of this article is to promote clear thinking and clear writing among students and teachers of psychological science by curbing terminological misinformation and confusion. To this end, we present a provisional list of 50 commonly used terms in psychology, psychiatry, and allied fields that should be avoided, or at most used sparingly and with explicit caveats. We provide corrective information for students, instructors, and researchers regarding these terms, which we organize for expository purposes into five categories: inaccurate or misleading terms, frequently misused terms, ambiguous terms, oxymorons, and pleonasms. For each term, we (a) explain why it is problematic, (b) delineate one or more examples of its misuse, and (c) when pertinent, offer recommendations for preferable terms. By being more judicious in their use of terminology, psychologists and psychiatrists can foster clearer thinking in their students and the field at large regarding mental phenomena.

Four broad temperament dimensions: description, convergent validation correlations, and comparison with the Big Five

A new temperament construct based on recent brain physiology literature has been investigated using the Fisher Temperament Inventory (FTI). Four collections of behaviors emerged, each associated with a specific neural system: the dopamine, serotonin, testosterone, and estrogen/oxytocin system. These four temperament suites have been designated: (1) Curious/Energetic, (2) Cautious/Social Norm Compliant, (3) Analytical/Tough-minded, and (4) Prosocial/Empathetic temperament dimensions. Two functional magnetic resonance imaging (fMRI) studies have suggested that the FTI can measure the influence of these neural systems. In this paper, to further the behavioral validation and characterization of the four proposed temperament dimensions, we measured correlations with five variables: (1) gender; (2) level of education; (3) religious preference; (4) political orientation; (5) the degree to which an individual regards sex as essential to a successful relationship. Subjects were 39,913 anonymous members of a US Internet dating site and 70,000+ members in six other countries. Correlations with the five variables characterize the FTI and are consistent with mechanisms using the proposed neuromodulators. We also report on an analysis between the FTI and the NEO-Five Factor Inventory, using a college sample (n = 215), which showed convergent validity. The results provide novel correlates not available in other questionnaires: religiosity, political orientation, and attitudes about sex in a relationship. Also, an Eigen analysis replicated the four clusters of co-varying items. The FTI, with its broad systems and non-pathologic factors complements existing personality questionnaires. It provides an index of some brain systems that contribute to temperament, and may be useful in psychotherapy, business, medicine, and the legal community.

Heritability estimates of the Big Five personality traits based on common genetic variants

According to twin studies, the Big Five personality traits have substantial heritable components explaining 40-60% of the variance, but identification of associated genetic variants has remained elusive. Consequently, knowledge regarding the molecular genetic architecture of personality and to what extent it is shared across the different personality traits is limited. Using genomic-relatedness-matrix residual maximum likelihood analysis (GREML), we here estimated the heritability of the Big Five personality factors (extraversion, agreeableness, conscientiousness, neuroticism and openness for experience) in a sample of 5011 European adults from 527,469 single-nucleotide polymorphisms across the genome. We tested for the heritability of each personality trait, as well as for the genetic overlap between the personality factors. We found significant and substantial heritability estimates for neuroticism (15%, s.e. = 0.08, P = 0.04) and openness (21%, s.e. = 0.08, P < 0.01), but not for extraversion, agreeableness and conscientiousness. The bivariate analyses showed that the variance explained by common variants entirely overlapped between neuroticism and openness (rG = 1.00, P < 0.001), despite low phenotypic correlation (r = - 0.09, P < 0.001), suggesting that the remaining unique heritability may be determined by rare or structural variants. As far as we are aware of, this is the first study estimating the shared and unique heritability of all Big Five personality traits using the GREML approach. Findings should be considered exploratory and suggest that detectable heritability estimates based on common variants is shared between neuroticism and openness to experiences.

The Fourth Law of Behavior Genetics

Behavior genetics is the study of the relationship between genetic variation and psychological traits. Turkheimer (2000) proposed "Three Laws of Behavior Genetics" based on empirical regularities observed in studies of twins and other kinships. On the basis of molecular studies that have measured DNA variation directly, we propose a Fourth Law of Behavior Genetics: "A typical human behavioral trait is associated with very many genetic variants, each of which accounts for a very small percentage of the behavioral variability." This law explains several consistent patterns in the results of gene discovery studies, including the failure of candidate gene studies to robustly replicate, the need for genome-wide association studies (and why such studies have a much stronger replication record), and the crucial importance of extremely large samples in these endeavors. We review the evidence in favor of the Fourth Law and discuss its implications for the design and interpretation of gene-behavior research.

Direct, indirect and pleiotropic effects of candidate genes on internalizing disorder psychopathology

BACKGROUND

Twin studies of internalizing disorders suggest that their high co-morbidity is partially explained by shared genetic risk. Few studies have investigated pleiotropic effects of well-validated candidate genes across phenotypes.

METHOD

Subjects were 928 Caucasian patients who presented to an out-patient clinic specializing in the assessment and treatment of anxiety and mood disorders. We constructed latent dimensional phenotypes across the internalizing spectrum (neuroticism, extraversion, depression, generalized anxiety, panic/agoraphobia, social phobia, post-traumatic stress, and obsessions-compulsions) by combining diagnostic criteria with other clinical indicators. We selected multiple variants in four evidence-based candidate genes (SLC6A4, COMT, GAD1, RGS2) with previously reported effects on several of these phenotypes. We conducted genetic association testing of their direct and indirect effects as well as gene × stress interactions (G × E).

RESULTS

We detected 19 nominally significant main effect associations for the 10 polymorphisms tested among the eight phenotypes (24%). These were generally phenotype non-specific, showing pleiotropic effects across multiple domains. The majority of observed sharing was between depression, panic disorder, and post-traumatic stress disorder. Some of these were best explained by mediational models in which genes increase liability for disorders indirectly via their effects on temperament. Limited G × E effects were detected between variants in SLC6A4 and both panic/agoraphobia and post-traumatic stress.

CONCLUSIONS

Examining just a few candidate genes for their potential roles in internalizing phenotypes, we found moderate support for the shared effects of several polymorphisms. These findings highlight the richness and complexity by which genes potentially contribute to psychopathology via pleiotropy, moderation by stress, and mediation by temperament.

Meta-analysis of Genome-wide Association Studies for Neuroticism, and the Polygenic Association With Major Depressive Disorder

IMPORTANCE

Neuroticism is a pervasive risk factor for psychiatric conditions. It genetically overlaps with major depressive disorder (MDD) and is therefore an important phenotype for psychiatric genetics. The Genetics of Personality Consortium has created a resource for genome-wide association analyses of personality traits in more than 63,000 participants (including MDD cases).

OBJECTIVES

To identify genetic variants associated with neuroticism by performing a meta-analysis of genome-wide association results based on 1000 Genomes imputation; to evaluate whether common genetic variants as assessed by single-nucleotide polymorphisms (SNPs) explain variation in neuroticism by estimating SNP-based heritability; and to examine whether SNPs that predict neuroticism also predict MDD.

DESIGN, SETTING, AND PARTICIPANTS

Genome-wide association meta-analysis of 30 cohorts with genome-wide genotype, personality, and MDD data from the Genetics of Personality Consortium. The study included 63,661 participants from 29 discovery cohorts and 9786 participants from a replication cohort. Participants came from Europe, the United States, or Australia. Analyses were conducted between 2012 and 2014.

MAIN OUTCOMES AND MEASURES

Neuroticism scores harmonized across all 29 discovery cohorts by item response theory analysis, and clinical MDD case-control status in 2 of the cohorts.

RESULTS

A genome-wide significant SNP was found on 3p14 in MAGI1 (rs35855737; P = 9.26 × 10-9 in the discovery meta-analysis). This association was not replicated (P = .32), but the SNP was still genome-wide significant in the meta-analysis of all 30 cohorts (P = 2.38 × 10-8). Common genetic variants explain 15% of the variance in neuroticism. Polygenic scores based on the meta-analysis of neuroticism in 27 cohorts significantly predicted neuroticism (1.09 × 10-12 < P < .05) and MDD (4.02 × 10-9 < P < .05) in the 2 other cohorts.

CONCLUSIONS AND RELEVANCE

This study identifies a novel locus for neuroticism. The variant is located in a known gene that has been associated with bipolar disorder and schizophrenia in previous studies. In addition, the study shows that neuroticism is influenced by many genetic variants of small effect that are either common or tagged by common variants. These genetic variants also influence MDD. Future studies should confirm the role of the MAGI1 locus for neuroticism and further investigate the association of MAGI1 and the polygenic association to a range of other psychiatric disorders that are phenotypically correlated with neuroticism.

GWA meta-analysis of personality in Korean cohorts

Personality is a determinant of behavior and lifestyle that is associated with health and human diseases. Despite the heritability of personality traits is well established, the understanding of the genetic contribution to personality trait variation is extremely limited. To identify genetic variants associated with each of the five dimensions of personality, we performed a genome-wide association (GWA) meta-analysis of three cohorts, followed by comparison of a family cohort. Personality traits were measured with the Revised NEO Personality Inventory for the five-factor model (FFM) of personality. We investigated the top five single-nucleotide polymorphisms (SNPs) for each trait, and revealed the most highly association with neuroticism and TACC2 (rs1010657, P=8.79 × 10(-7)), extraversion and PTPN12 (rs12537271, P=1.47 × 10(-7)), openness and IMPAD1 (rs16921695, P=5 × 10(-8)), agreeableness and RPS29 (rs8015351, P=1.27 × 10(-6)) and conscientiousness and LMO4 (rs912765, P=2.91 × 10(-6)). It had no SNP reached the GWA study threshold (P<5 × 10(-8)). When expanded the SNPs up to top 100, the correlation of PTPRD (rs1029089) and agreeableness was confirmed in Healthy Twin cohort with other 13 SNPs. This GWA meta-analysis on FFM personality traits is meaningful as it was the first on a non-Caucasian population targeted to FFM of personality traits.

Retinal microvessels reflect familial vulnerability to psychotic symptoms: A comparison of twins discordant for psychotic symptoms and controls

Mounting evidence suggests that individuals with schizophrenia have an underlying vulnerability to cardiovascular disease, and a recent study suggested that this vulnerability might be reflected in the retinal microvasculature. The purpose of this study was to test the hypothesis that the retinal microvessels reflect familial vulnerability to psychotic symptoms. Participants were 531 adolescent and young adult twins who took part in the Brisbane Longitudinal Twin Study and the Twins Eye Study in Tasmania. The twins had photographs taken of their retina when they were adolescents or young adults (M age=20.6 years), and retinal vessel diameter was assessed using computer software. The twins completed an assessment of psychosis symptoms approximately six years later. We compared retinal venular diameters of individuals with one or more symptoms of psychosis (n=45), their unaffected co-twins (n=24), and controls (n=462). Individuals with one or more symptoms of psychosis had wider venules (standardized mean=0.29) than controls (standardized mean=-0.04; p=.03), and unaffected co-twins had venular diameters that were intermediate (standardized mean=0.13) between the two groups, suggesting that wide venules may represent a proxy marker of familial vulnerability to psychosis symptoms. Consistent with previous work, there were no differences in arteriolar diameter between individuals with and without symptoms of psychosis. Findings suggest that wide retinal venules may serve as a proxy marker of familial liability to psychosis symptoms. The pathophysiological mechanisms linking psychosis and cardiovascular disease may be operative from early in life, possibly at the level of the microvasculature.

Personality and well-being in adolescents

Different profiles of the character dimensions of self-directedness, cooperativeness and self-transcendence result in different levels of wellbeing among adults. However, the influence of the multidimensional character profiles on adolescents' composite wellbeing remains unexplored. This study builds on previous studies with adults, and examines the linear and non-linear associations between the dimensions of the psychobiological model of personality and well-being in adolescents. Participated in this study 1540 adolescents (M = 15.44, SD = 1.731). Personality was assessed using the Temperament and Character Inventory (TCI). Well-being was evaluated in a composite perspective: satisfaction with social support, health-related quality of life, satisfaction with life and affect. Variable-centered and individual-centered analyses were performed. Self-directedness was strongly associated with all dimensions of affective and cognitive well-being regardless of the other two character traits. Cooperativeness was associated with non-affective well-being and with positive affect, but only when associated to elevation of Self-directedness and Self-transcendence. Self-Directedness and Cooperativeness explained 15.5% of the non-affective well-being variance. Self-Directedness and Self-Transcendence explained 10.4% of the variance in affective well-being. This study confirms the tendencies found in previous studies with adults from other societies, where each character dimension gives an independent contribution to well-being depending on the interactions with other Character dimensions. Also, this study highlights the importance of considering the non-linear influences of the character dimensions in understanding of adolescents' wellbeing. These results have strong implications for youth positive mental health promotion, including for school-based policies and practices.

Brain derived neurotrophic factor gene (BDNF) and personality traits: the modifying effect of season of birth and sex

Personality traits are complex phenotypes influenced by interactions of multiple genetic variants of small effect and environmental factors. It has been suggested that the brain derived neurotrophic factor gene (BDNF) is involved in personality traits. Season of birth (SOB) has also been shown to affect personality traits due to its influences on brain development during prenatal and early postnatal periods. The present study aimed to investigate the effects of BDNF on personality traits; and the modifying effects of SOB and sex on associations between BDNF and personality traits. A sample of 1018 young adults (68% women; age range 17-25years) of Caucasian origin from the Russian Federation was assessed on personality traits (Novelty Seeking, Harm Avoidance, Reward Dependence, Persistence, Self-directedness, Cooperativeness, Self-transcendence) with the Temperament and Character Inventory-125 (TCI-125). Associations between personality traits and 12 BDNF SNPs were tested using linear regression models. The present study demonstrated the effect of rs11030102 on Persistence in females only (PFDR=0.043; r(2)=1.3%). There were significant interaction effects between Val66Met (rs6265) and SOB (PFDR=0.048, r(2)=1.4%), and between rs2030323 and SOB (PFDR=0.042, r(2)=1.3%), on Harm Avoidance. Our findings provide evidence for the modifying effect of SOB on the association between BDNF and Harm Avoidance, and for the modifying effect of sex on the association between BDNF and Persistence.

Replicability and robustness of genome-wide-association studies for behavioral traits

A recent genome-wide-association study of educational attainment identified three single-nucleotide polymorphisms (SNPs) whose associations, despite their small effect sizes (each R (2) ≈ 0.02%), reached genome-wide significance (p < 5 × 10(-8)) in a large discovery sample and were replicated in an independent sample (p < .05). The study also reported associations between educational attainment and indices of SNPs called "polygenic scores." In three studies, we evaluated the robustness of these findings. Study 1 showed that the associations with all three SNPs were replicated in another large (N = 34,428) independent sample. We also found that the scores remained predictive (R (2) ≈ 2%) in regressions with stringent controls for stratification (Study 2) and in new within-family analyses (Study 3). Our results show that large and therefore well-powered genome-wide-association studies can identify replicable genetic associations with behavioral traits. The small effect sizes of individual SNPs are likely to be a major contributing factor explaining the striking contrast between our results and the disappointing replication record of most candidate-gene studies.

Sperm competition in humans: mate guarding behavior negatively correlates with ejaculate quality

In species where females mate with multiple males, the sperm from these males must compete to fertilise available ova. Sexual selection from sperm competition is expected to favor opposing adaptations in males that function either in the avoidance of sperm competition (by guarding females from rival males) or in the engagement in sperm competition (by increased expenditure on the ejaculate). The extent to which males may adjust the relative use of these opposing tactics has been relatively neglected. Where males can successfully avoid sperm competition from rivals, one might expect a decrease in their expenditure on tactics for the engagement in sperm competition and vice versa. In this study, we examine the relationship between mate guarding and ejaculate quality using humans as an empirical model. We found that men who performed fewer mate guarding behaviors produced higher quality ejaculates, having a greater concentration of sperm, a higher percentage of motile sperm and sperm that swam faster and less erratically. These effects were found independent of lifestyle factors or factors related to male quality. Our findings suggest that male expenditure on mate guarding and on the ejaculate may represent alternative routes to paternity assurance in humans.

Increased functional connectivity within mesocortical networks in open people

Openness is a personality trait reflecting absorption in sensory experience, preference for novelty, and creativity, and is thus considered a driving force of human evolution. At the brain level, a relation between openness and dopaminergic circuits has been proposed, although evidence to support this hypothesis is lacking. Recent behavioral research has also found that people with mania, a psychopathological condition linked to dopaminergic dysfunctions, may display high levels of openness. However, whether openness is related to dopaminergic circuits has not been determined thus far. We addressed this issue via three functional magnetic resonance imaging (fMRI) experiments in n=46 healthy volunteers. In the first experiment participants lied at rest in the scanner while in the other two experiments they performed active tasks that included the presentation of pleasant odors and pictures of food. Individual differences in openness and other personality traits were assessed via the NEO-PI-R questionnaire (NEO-Personality Inventory-Revised), a widely employed measure of the five-factor model personality traits. Correlation between fMRI and personality data was analyzed via state-of-art methods assessing resting-state and task-related functional connectivity within specific brain networks. Openness was positively associated with the functional connectivity between the right substantia nigra/ventral tegmental area, the major source of dopaminergic inputs in the brain, and the ipsilateral dorsolateral prefrontal cortex (DLPFC), a key region in encoding, maintaining, and updating information that is relevant for adaptive behaviors. Of note, the same connectivity pattern was consistently found across all of the three fMRI experiments. Given the critical role of dopaminergic signal in gating information in DLPFC, the increased functional connectivity within mesocortical networks in open people may explain why these individuals display a wide "mental permeability" to salient stimuli and an increased absorption in sensory experience.

Genetic and environmental continuity in personality development: a meta-analysis

The longitudinal stability of personality is low in childhood but increases substantially into adulthood. Theoretical explanations for this trend differ in the emphasis placed on intrinsic maturation and socializing influences. To what extent does the increasing stability of personality result from the continuity and crystallization of genetically influenced individual differences, and to what extent does the increasing stability of life experiences explain increases in personality trait stability? Behavioral genetic studies, which decompose longitudinal stability into sources associated with genetic and environmental variation, can help to address this question. We aggregated effect sizes from 24 longitudinal behavioral genetic studies containing information on a total of 21,057 sibling pairs from 6 types that varied in terms of genetic relatedness and ranged in age from infancy to old age. A combination of linear and nonlinear meta-analytic regression models were used to evaluate age trends in levels of heritability and environmentality, stabilities of genetic and environmental effects, and the contributions of genetic and environmental effects to overall phenotypic stability. Both the genetic and environmental influences on personality increase in stability with age. The contribution of genetic effects to phenotypic stability is moderate in magnitude and relatively constant with age, in part because of small-to-moderate decreases in the heritability of personality over child development that offset increases in genetic stability. In contrast, the contribution of environmental effects to phenotypic stability increases from near zero in early childhood to moderate in adulthood. The life-span trend of increasing phenotypic stability, therefore, predominantly results from environmental mechanisms.

Impact of behavioral genetic evidence on the perceptions and dispositions of child abuse victims

BACKGROUND

Behavioral genetic research is beginning to elucidate some of the genetic contributions to human behaviors - including criminal and other problematic behaviors - and their interactions with environmental influences. One of the most studied of these interactions involves low-activity alleles of the monoamine oxidase A (MAOA) gene, which appear to increase the risk of antisocial behavior among males in the wake of childhood maltreatment. Some scholars have suggested that decisions about disposition of child abuse victims should be shaped by these findings, but the extent of public support for such approaches has not been assessed.

METHODS

In this study, a representative sample of the US population (n = 250) was presented with a vignette about a child, physically abused by his mother, who was tested for the presence of an allele that increases the risk of future impulsive violent behavior. Participants were asked about their views regarding the child's disposition, including return to his mother, and medical or psychological treatment.

RESULTS

Although participants thought that genetic data should be taken into account, the presence of an allele that increases the risk of impulsive violent behavior did not affect views regarding the child's return to his mother. However, it did increase respondents' willingness to provide the child with medical treatment and their view of the child as dangerous to other children.

CONCLUSIONS

The findings suggest that behavioral genetic evidence has effects on perceptions of dangerousness and tendencies to view problems as medical but that the public is cautious about the use of genetic findings in child abuse adjudications.

Genetic variation associated with differential educational attainment in adults has anticipated associations with school performance in children

Genome-wide association study results have yielded evidence for the association of common genetic variants with crude measures of completed educational attainment in adults. Whilst informative, these results do not inform as to the mechanism of these effects or their presence at earlier ages and where educational performance is more routinely and more precisely assessed. Single nucleotide polymorphisms exhibiting genome-wide significant associations with adult educational attainment were combined to derive an unweighted allele score in 5,979 and 6,145 young participants from the Avon Longitudinal Study of Parents and Children with key stage 3 national curriculum test results (SATS results) available at age 13 to 14 years in English and mathematics respectively. Standardised (z-scored) results for English and mathematics showed an expected relationship with sex, with girls exhibiting an advantage over boys in English (0.433 SD (95%CI 0.395, 0.470), p<10(-10)) with more similar results (though in the opposite direction) in mathematics (0.042 SD (95%CI 0.004, 0.080), p = 0.030). Each additional adult educational attainment increasing allele was associated with 0.041 SD (95%CI 0.020, 0.063), p = 1.79×10(-04) and 0.028 SD (95%CI 0.007, 0.050), p = 0.01 increases in standardised SATS score for English and mathematics respectively. Educational attainment is a complex multifactorial behavioural trait which has not had heritable contributions to it fully characterised. We were able to apply the results from a large study of adult educational attainment to a study of child exam performance marking events in the process of learning rather than realised adult end product. Our results support evidence for common, small genetic contributions to educational attainment, but also emphasise the likely lifecourse nature of this genetic effect. Results here also, by an alternative route, suggest that existing methods for child examination are able to recognise early life variation likely to be related to ultimate educational attainment.

Harmonization of Neuroticism and Extraversion phenotypes across inventories and cohorts in the Genetics of Personality Consortium: an application of Item Response Theory

Mega- or meta-analytic studies (e.g. genome-wide association studies) are increasingly used in behavior genetics. An issue in such studies is that phenotypes are often measured by different instruments across study cohorts, requiring harmonization of measures so that more powerful fixed effect meta-analyses can be employed. Within the Genetics of Personality Consortium, we demonstrate for two clinically relevant personality traits, Neuroticism and Extraversion, how Item-Response Theory (IRT) can be applied to map item data from different inventories to the same underlying constructs. Personality item data were analyzed in >160,000 individuals from 23 cohorts across Europe, USA and Australia in which Neuroticism and Extraversion were assessed by nine different personality inventories. Results showed that harmonization was very successful for most personality inventories and moderately successful for some. Neuroticism and Extraversion inventories were largely measurement invariant across cohorts, in particular when comparing cohorts from countries where the same language is spoken. The IRT-based scores for Neuroticism and Extraversion were heritable (48 and 49 %, respectively, based on a meta-analysis of six twin cohorts, total N = 29,496 and 29,501 twin pairs, respectively) with a significant part of the heritability due to non-additive genetic factors. For Extraversion, these genetic factors qualitatively differ across sexes. We showed that our IRT method can lead to a large increase in sample size and therefore statistical power. The IRT approach may be applied to any mega- or meta-analytic study in which item-based behavioral measures need to be harmonized.

A mixed-binomial model for Likert-type personality measures

Personality measurement is based on the idea that values on an unobservable latent variable determine the distribution of answers on a manifest response scale. Typically, it is assumed in the Item Response Theory (IRT) that latent variables are related to the observed responses through continuous normal or logistic functions, determining the probability with which one of the ordered response alternatives on a Likert-scale item is chosen. Based on an analysis of 1731 self- and other-rated responses on the 240 NEO PI-3 questionnaire items, it was proposed that a viable alternative is a finite number of latent events which are related to manifest responses through a binomial function which has only one parameter—the probability with which a given statement is approved. For the majority of items, the best fit was obtained with a mixed-binomial distribution, which assumes two different subpopulations who endorse items with two different probabilities. It was shown that the fit of the binomial IRT model can be improved by assuming that about 10% of random noise is contained in the answers and by taking into account response biases toward one of the response categories. It was concluded that the binomial response model for the measurement of personality traits may be a workable alternative to the more habitual normal and logistic IRT models.

Genetic strategies for probing conscientiousness and its relationship to aging

Conscientiousness is an important trait for understanding healthy aging. The present article addresses how behavioral and molecular genetics methodologies can aid in furthering explicating the link between conscientiousness and aspects of health and well-being in later life. We review the etiology of conscientiousness documented by both quantitative and molecular genetics methods. We also discuss the ways behavior genetics can be used to continue to help refine the concept of conscientiousness and to help identify points of etiological overlap between conscientiousness and healthy aging outcomes. Phenotypic research has established nontrivial associations between conscientiousness and important outcomes, but behavior genetic methods can determine what the causal (genetic and environmental) mechanisms are behind these relationships. An empirical example of one of these techniques is provided using twin data from the Midlife in the United States (MIDUS) study. We demonstrate that conscientiousness moderates genetic and environmental influences on problem alcohol use, such that greater levels of conscientiousness buffer against the random effects of the environment. Finally, suggestions for future work in this area are discussed.