Molecular genetics of personality

Identification of Candidate Genes and Pathways Linked to the Temperament Trait in Sheep

Temperament can be defined as the emotional variability among animals of the same species in response to the same stimulus, grouping animals by their reactivity as nervous, intermediate, or calm. Our goal was to identify genomic regions with the temperament phenotype measured by the Isolation Box Test (IBT) by single-step genome-wide association studies (ssGWAS). The database consisted of 4317 animals with temperament records, and 1697 genotyped animals with 38,268 effective Single Nucleotide Polymorphism (SNP) after quality control. We identified three genomic regions that explained the greatest percentage of the genetic variance, resulting in 25 SNP associated with candidate genes on chromosomes 6, 10, and 21. A total of nine candidate genes are reported for the temperament trait, which is: PYGM, SYVN1, CAPN1, FADS1, SYT7, GRID2, GPRIN3, EEF1A1 and FRY, linked to the energetic activity of the organism, synaptic transmission, meat tenderness, and calcium associated activities. This is the first study to identify these genetic variants associated with temperament in sheep, which could be used as molecular markers in future behavioral research.

Gene polymorphisms associated with temperament

When individuals are exposed to stressful environmental challenges, the response varies widely in one or more of three components: psychology, behavior and physiology. This variability among individuals can be defined as temperament. In recent years, an increasing large body of evidence suggests that the dimensions of temperament, as well as personality, psychological disorders and behavioral traits, are influenced by genetic factors, and much of the variation appears to involve variation in genes or gene polymorphisms in the hypothalamic-pituitary-adrenocortical (HPA) axis and the behavior-controlling neurotransmitter networks. Here, we review our current understanding of the probabilistic impact of a number of candidate gene polymorphisms that control temperament, psychological disorders and behavioral traits in animals and human, including the gene polymorphisms related to corticotrophin-releasing hormone (CRH) production and adrenal cortisol production involved in the HPA axis, and a large number of gene polymorphisms in the dopaminergic and serotonergic neurotransmitter networks. It will very likely to assist in diagnosis and treatment of human relevant disorders, and provide useful contributions to our understanding of evolution, welfare and conservation, for animals in the wild and in production systems. Additionally, investigations of gene-gene and gene-environment complex interactions in humans and animals need further clear illustration.

ABO Blood Type and Personality Traits in Healthy Japanese Subjects

There is no scientific consensus that a relationship exists between the ABO blood group and personality traits. However, a recent study hypothesized that the dopamine beta-hydroxylase (DBH) gene is in linkage with the ABO gene. The sample population consisted of 1,427 healthy Japanese subjects who completed the Temperament and Character Inventory (TCI). Each subject's ABO blood type was determined by genotyping the rs8176719 and rs8176746 ABO gene single-nucleotide polymorphisms (SNPs) using a TaqMan genotyping assay. The relationships between the six ABO genotypes or four ABO phenotypes and personality traits were examined using a multivariate analysis of covariance (MANCOVA), controlling for age and sex. The MANCOVA data showed a significant difference in TCI scores among the ABO genotype groups (F [7, 1393] = 3.354, p = 0.001). A subsequent univariate analysis showed a significant difference in the mean scores for Persistence among the genotype groups (F = 2.680, partial η2 = 0.010, p = 0.020). Similarly, dividing the ABO blood type into four phenotypes revealed a significant difference among the phenotype groups (F [7, 1397] = 2.529, p = 0.014). A subsequent univariate analysis showed a significant difference among the phenotype groups in the mean scores for Persistence (F = 2.952, partial η2= 0.006, p = 0.032). We observed a significant association between ABO blood group genotypes and personality traits in a large number of healthy Japanese subjects. However, these results should be regarded as preliminary and should be interpreted with caution because it is possible that the association between ABO blood group genotype and the Persistence trait is relatively weak.

Genetic similarities between tobacco use disorder and related comorbidities: an exploratory study

Background

Tobacco use disorder (TUD), defined as the use of tobacco to the detriment of a person’s health or social functioning, is associated with various disorders. We hypothesized that mutual variation in genes may partly explain this link. The aims of this study were to make a non-exhaustive inventory of the disorders using (partially) the same genetic pathways as TUD, and to describe the genetic similarities between TUD and the selected disorders.

Methods

We developed a 3 stage approach: (i) selection of genes influencing TUD using Gene2Mesh and Ingenuity Pathway Analysis (IPA), (ii) selection of disorders associated with the selected genes using IPA and (iii) genetic similarities between disorders associated with TUD using Jaccard distance and cluster analyses.

Results

Fourteen disorders and thirty-two genes met our inclusion criteria. The Jaccard distance between pairs of disorders ranged from 0.00 (e.g. oesophageal cancer and malignant hypertension) to 0.45 (e.g. bladder cancer and addiction). A lower number in the Jaccard distance indicates a higher similarity between the two disorders. Two main clusters of genetically similar disorders were observed, one including coexisting disorders (e.g. addiction and alcoholism) and the other one with the side-effects of smoking (e.g. gastric cancer and malignant hypertension).

Conclusions

This exploratory study partly explains the potential genetic components linking TUD to other disorders. Two principle clusters of disorders were observed (i) coexisting disorders of TUD and (ii) side-effects of TUD disorders. A further deepening of this observation in a real life study should allow strengthening this hypothesis.

Dopamine transporter dysfunction in Han Chinese people with chronic methamphetamine dependence after a short-term abstinence

Single-photon emission-computed tomography (SPECT) after the administration of (99m)Tc-TRODAT-1 was performed on healthy subjects and subjects with methamphetamine (METH)dependence at time 1 (T1) after 24-48 h of abstinence, time 2 (T2) after 2 weeks of abstinence, and time 3 (T3) after 4 weeks of abstinence. In contrast to values in controls, the values of the striatal DAT specific uptake ratios (SURs) in subjects with METH dependence were significantly lower at T1 (n=25), T2 (n=9), and T3 (n=8); a mild increase in SURs was observed at T2 and T3, but values were still significantly lower than those in controls. In subjects with METH dependence, there was a trend for a negative correlation of striatal DAT SURs and craving for METH at T1. METH craving, anxiety and depression scores significantly decreased from T1 to T2 to T3. We conclude that Han Chinese people with METH dependence experience significant striatal DAT dysfunction, and that these changes may be mildly reversible after 4 weeks of abstinence, but that DAT levels still remain significantly lower than those in healthy subjects. The mild recovery of striatal DAT may parallel improvements in craving, anxiety and depression.

QTL analysis of behavior in nine-spined sticklebacks (Pungitius pungitius)

The genetic architecture of behavioral traits is yet relatively poorly understood in most non-model organisms. Using an F2-intercross (n = 283 offspring) between behaviorally divergent nine-spined stickleback (Pungitius pungitius) populations, we tested for and explored the genetic basis of different behavioral traits with the aid of quantitative trait locus (QTL) analyses based on 226 microsatellite markers. The behaviors were analyzed both separately (viz. feeding activity, risk-taking and exploration) and combined in order to map composite behavioral type. Two significant QTL-explaining on average 6 % of the phenotypic variance-were detected for composite behavioral type on the experiment-wide level, located on linkage groups 3 and 8. In addition, several suggestive QTL located on six other linkage groups were detected on the chromosome-wide level. Apart from providing evidence for the genetic basis of behavioral variation, the results provide a good starting point for finer-scale analyses of genetic factors influencing behavioral variation in the nine-spined stickleback.

The Elevated Plus-Maze Test: Differential Psychopharmacology of Anxiety-Related Behavior

The role of individual factors in behavioral neuroscience is an important, but still neglected, area of research. For example, the Elevated Plus-Maze Test has been one of the most used paradigms to gauge unconditioned aversively motivated behavior in rodents. However, despite a great number of experiments with this test there have been only few efforts to assess systematic individual variations in the elevated plus-maze and related neurobiological functions. The present review aims to give, first, a general overview and introduction about the test, and second, an animal model of anxiety based on natural variance of plus-maze behavior within a given unselected population of rats. Finally, critical aspects of such approaches in animal research are discussed, and suggestions are given as to where to go from here.

NCAM1, TACR1 and NOS genes and temperament: a study on suicide attempters and controls

Suicide, one of the leading causes of death among young adults, seems to be plausibly modulated by both genetic and personality factors. The aim of this study was to dissect the potential association between genetics and temperament in a sample of 111 suicide attempters and 289 healthy controls. We focused on 4 genes previously investigated in association with suicide on the same sample: the nitric oxide synthase 1 and 3 (NOS1 and NOS3), the neuronal cell adhesion molecule 1 (NCAM1), and the tachykinin receptor 1 (TACR1) genes. In particular, we investigated whether a set of genetic variants in these genes (NOS1: rs2682826, rs1353939, rs693534; NOS3: rs2070744, rs1799983, rs891512; NCAM1: rs2301228, rs1884, rs1245113, rs1369816, rs2196456, rs584427; TACR1: rs3771810, rs3771825, rs726506, rs1477157) were associated with temperamental traits at the Temperament and Character Inventory (TCI). No strong evidence was found for the association between TCI personality traits and the polymorphisms considered in the 4 genes, with the exception of an association between reward dependence trait and the rs2682826 SNP in NOS1 in the healthy sample. However, this result could be plausibly interpreted as a false-positive finding. In conclusion, our study did not support the thesis of a direct modulation of these genes on temperament; however, further studies on larger samples are clearly required in order to confirm our preliminary findings and to exclude any possible minor influence.

Personality Measurement and Assessment in Large Panel Surveys*

Personality tests are being added to large panel studies with increasing regularity, such as the Health and Retirement Study (HRS). To facilitate the inclusion and interpretation of these tests, we provide some general background on personality psychology, personality assessment, and the validity of personality tests. In this review, we provide background on definitions of personality, the strengths and weaknesses of the self-report approaches to personality testing typically used in large panel studies, and the validity of personality tests for three outcomes: genetics, income, and health. We conclude with recommendations on how to improve personality assessment in future panel studies.

Association between the estrogen receptor TA polymorphism and Harm avoidance

In the last decade a large number of studies focused on the recognition of gene variants modulating temperamental traits. The gene coding for the estrogen receptor alpha (ESR1) appears to be an interesting candidate and it has been found to be linked to Harm avoidance (HA). The aim of the present study was to investigate whether the ESR1 TA dinucleotide repeat polymorphism is associated with HA temperamental trait in a sample of Caucasian University students. One hundred ninety healthy subjects were genotyped for ESR1 TA dinucleotide repeat polymorphism and were administered the Temperament and Character Inventory (TCI). ESR1 TA repeat lengths were dichotomized into short and long categories. ANOVA was used to examine the influence of ESR1 variants (short/long) on the means of the TCI HA scores. HA was significantly associated with age and gender in our sample, being higher in older and female subjects. In the global sample as well as in men and women separately, individuals carrying the S/S variant showed significantly higher HA scores. Further analysis on the HA subscales revealed that specific differences could exist between men and women. Our results further suggest a possible role of ESR1 variants on HA. Further research is needed to replicate our findings as well as to better explore the neuro-biological mechanisms of the modulation of ESR1 on HA.

Investigation of 17 candidate genes for personality traits confirms effects of the HTR2A gene on novelty seeking

Genes involved in serotonergic and dopaminergic neurotransmission have been hypothesized to affect different aspects of personality, but findings from genetic association studies did not provide conclusive results so far. In previous studies, however, only one or a few polymorphisms within single genes were investigated neglecting the possibility that the genetic associations might be more complex comprising several genes or gene regions. To overcome this limitation, we performed an extended genetic association study analyzing 17 serotonergic (SLC6A4, HTR1A, HTR1B, HTR2A, HTR2C, HTR3A, HTR6, MAOA, TPH1, TPH2) and dopaminergic genes (SLC6A3, DRD2, DRD3, DRD4, COMT, MAOA, TH, DBH), which have been previously reported to be implicated with personality traits. One hundred and ninety-five single nucleotide polymorphisms (SNPs) within these genes were genotyped with the Illumina BeadChip technology (HumanHap300, Human-1) in a sample of 366 mentally healthy Caucasians. Additionally, we tried to replicate our results in an independent sample of further 335 Caucasians. Personality traits in both samples were assessed with the German version of Cloninger's Tridimensional Personality Questionnaire. From 30 SNPs showing associations at a nominal level of significance, two intronic SNPs, rs2770296 and rs927544, both located in the HTR2A gene, withstood correction for multiple testing. These SNPs were associated with the personality trait novelty seeking. The effect of rs927544 could be replicated for the novelty seeking subscale extravagance, and the same SNP was also associated with extravagance in the combined samples. Our results show that HTR2A polymorphisms modulate facets of novelty seeking behaviour in healthy adults suggesting that serotonergic neurotransmission is involved in this phenotype.

GABA and homovanillic acid in the plasma of Schizophrenic and bipolar I patients

We have determined the plasma (p) concentration of gamma-aminobutyric acid (GABA) and the dopamine metabolite homovanillic acid (HVA), and the pHVA/pGABA ratio in schizophrenic and bipolar patients. The research was undertaken in a geographic area with an ethnically homogeneous population. The HVA plasma concentrations were significantly elevated in the schizophrenic patients compared to the bipolar patients. The levels of pGABA was significantly lower in the two groups of patients compared to the control group, while the pHVA/pGABA ratio was significantly greater in the both groups of patients compared to the controls. As the levels of pHVA and pGABA are partially under genetic control it is better to compare their concentrations within an homogeneous population. The values of the ratio pHVA/pGABA are compatible with the idea of an abnormal dopamine-GABA interaction in schizophrenic and bipolar patients. The pHVA/pGABA ratio may be a good peripheral marker in psychiatric research.

Serotonin receptor HTR1A and HTR2C variants and personality traits in suicide attempters and controls

INTRODUCTION

Serotonin has been extensively studied in relation to both personality features and suicidal behaviours.

OBJECTIVE

In this study, we considered the association between the serotonin receptor 1A (HTR1A) and 2C (HTR2C) SNPs and personality traits, as measured by the Temperament and Character Inventory (TCI), in a sample of suicide patients and healthy volunteers.

METHODS

The SNPs considered were, for HTR1A rs1423691, rs878567 and rs6295, and for HTR2C rs547536, rs2192372, rs6318, rs2428707, rs4272555 and rs1801412. The sample was composed of three groups: two German samples, consisting of a healthy control group of 289 subjects (42.6% males, mean age: 45.2+/-14.9) and a psychiatric patient group of 111 suicide attempters (38.7% males, mean age: 39.2+/-13.6), and an Italian sample, composed of 64 mood disorder patients (35.9% males, mean age: 43.0+/-14.8). In the German samples all the SNPs were investigated, while in the Italian sample only the HTR1A rs6295 and the HTR2C rs6318 SNPs were considered.

RESULTS

Controlling for sex, age and educational level, single markers and haplotypes were not or only marginally associated with personality dimensions.

CONCLUSIONS

Our study does not support the role of HTR1A and HTR2C gene variants on personality traits in both healthy volunteers and mood disorder patients.

An interaction between the norepinephrine transporter and monoamine oxidase A polymorphisms, and novelty-seeking personality traits in Korean females

The personality traits associated with the noradrenergic system have not yet been clearly established. In the present study, we investigated the variable number of tandem repeats (VNTR) polymorphism of the norepinephrine transporter (NET) and monoamine oxidase A (MAOA), which are major components of the adrenergic system, to elucidate their relationship with personality. A total of 245 normal female Koreans (age 23.05+/-3.07 years, mean+/-SD) volunteered to take part in this study. They filled out a Korean version of the Temperament and Character Inventory (TCI) and were genotyped for the NET and MAOA-VNTR; the NET T-182C and MAOA-uVNTR polymorphisms were checked. We found significant main effect of NET genotype on novelty seeking (NS) score (F=5.43, p=0.021) and significant interaction between the NET and MAOA-uVNTR polymorphisms on NS score (F=11.06, p=0.001). However, there were no relationship between MAOA-uVNTR polymorphisms and NS score, and no association with other temperamental dimensions and these two polymorphisms. Our findings suggest that this functional polymorphism in the noradrenergic gene is associated with novelty seeking in Korean females.

Genetically dependent modulation of serotonergic inactivation in the human prefrontal cortex

Previous research suggests that genetic variations regulating serotonergic neurotransmission mediate individual differences in the neural network underlying impulsive and aggressive behaviour. Although with conflicting findings, the monoamine oxidase-A (MAOA) and the serotonin transporter (5HTT) gene polymorphisms have been associated with an increased risk to develop impulsive and aggressive behaviour. Double knock-out mice studies have also demonstrated that MAOA and 5HTT genes strongly interact in the metabolic pathway leading to the serotonergic inactivation; however, their potential interactive effect in human brain remains uninvestigated. We used blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) to assess the independent and interactive effects of both MAOA and 5HTT polymorphisms on the brain activity elicited by a response inhibition task in healthy volunteers. Multivariate analysis demonstrated an individual effect of both MAOA and 5HTT polymorphisms and a strong allele-allele interaction in the anterior cingulate cortex (ACC), a key region implicated in cognitive control and in the pathophysiology of impulsive and aggressive behaviour. These findings suggest that the MAOAx5HTT allelic interaction exerts a significant modulation on the BOLD response associated with response inhibition and contribute to validate haplotype models as useful tools for a better understanding of the neurobiology underlying complex cognitive functions.

Specific personality traits and dopamine, serotonin genes in anxiety-depressive alcoholism among Han Chinese in Taiwan

BACKGROUND

Cloninger [Cloninger CR. 1987. Neurogenetic adaptive mechanisms in alcoholism. Science 236: 410-416.] had proposed a psychobiological model suggesting that three main personality dimensions distinguish the alcoholism into two subtypes (type I and type II). However, the classification was equivocal for clinical diagnosis. Recently, anxiety-depressive alcohol dependence (ANX/DEP ALC) has been posited as a genetically specific subtype of alcoholism. Its clinical characteristics were similar to individuals with type I alcoholism [Cloninger, C.R. 1987. Neurogenetic adaptive mechanisms in alcoholism. Science 236: 410-6.] such as having a high comorbidity with mood disorder, late-onset and more anxious/depressed traits. We attempted to investigate whether the dopamine D2 receptor (DRD2) and the serotonin transporter promoter region (5-HTTLPR) genes were involved in Novelty Seeking (NS) and Harm Avoidance (HA) of ANX/DEP ALC.

METHODS

We recruited 46 pure alcohol dependents (Pure ALC) and 87 anxiety-depression alcohol dependents (ANX/DEP ALC). All participants were diagnosed by DSM-IV criteria, genotyped by the PCR method and assessed with Tridimensional Personality Questionnaire (TPQ).

RESULTS

Both NS and HA were high in ANX/DEP ALC (p = 0.021; p = 0.001, respectively). The association between NS and ANX/DEP ALC only existed in subjects with DRD2 TaqI A1(+) allele (A1/A1 or A1/A2 genotypes) (p = 0.004) and in those with S/S genotype of 5-HTTLPR (p = 0.005). With the stratification of DRD2 TaqI A1(+) allele, high NS of ANX/DEP ALC existed only in carriers of 5-HTTLPR S/S genotype (p=0.001). Moreover, ANX/DEP ALC was related to high HA only in samples carrying 5-HTTLPR S/L or L/L genotype (p = 0.02).

CONCLUSIONS

These findings provided the empirical genetic characterization of the specific personality traits in ANX/DEP ALC among Han Chinese population in Taiwan.

5-HT2A SNPs and the Temperament and Character Inventory

Temperamental traits, the most basic part of personality, have been largely correlated with neurotransmitter systems and are under genetic control. Among serotonin candidates, the 2A receptor (5-HT(2A)) received considerable attention. We analyzed four SNPs (rs643627, rs594242, rs6311 and rs6313) in the 5-HT(2A) gene and their association with personality traits, as measured with the Temperament and Character Inventory (TCI). The sample was composed of three sub-groups: two German sub-samples, consisting of a healthy group of 289 subjects (42.6% males, mean age: 45.2+/-14.9) and a psychiatric patient group of 111 suicide attempters (38.7% males, mean age: 39.2+/-13.6), and an Italian sub-sample, composed of 60 mood disorder patients (35.0% males, mean age: 44.0+/-14.8). Controlling for sex, age and educational level, the SNPs were not strongly associated with personality dimensions. Only the rs594242 showed an association with Self-Directedness (p=0.003) in the German sample, while rs6313 was marginally associated with Novelty Seeking (p=0.01) in the Italian sample. We conclude that 5-HT(2A) SNPs may marginally modulate personality traits but further studies are required.

The molecular genetic architecture of human personality: beyond self-report questionnaires

Molecular genetic studies of personality began with two high impact papers in 1996 that showed provisional associations between the dopamine DRD4 exon III repeat region and Novelty Seeking/Extraversion. These first two reports were shortly followed by an investigation linking Neuroticism/Harm Avoidance with the serotonin transporter (SLC6A4) promoter region polymorphism (5-HTTLPR). In the ensuing decade, thousands of subjects have been studied for association between these genes and personality, assessed by using self-report questionnaires, with erratic success in replication of the first findings for Novelty Seeking (DRD4) and Harm Avoidance (5-HTTLPR). Small effect sizes characteristic of non-Mendelian traits, polygenic patterns of inheritance and true heterogeneity between studies confound attempts to reach a consensus regarding the role of common polymorphisms in contributing to personality domains. Nevertheless, the current state of personality genetics is far from being bleak. Several new paradigms especially functional neuroimaging or 'imaging genomics' have strengthened the connection between 5-HTTLPR and anxiety-related personality traits. The demonstrations that early environmental information can considerably strengthen and even uncover associations between genes and behavior (Caspi's seminal studies and more recently the demonstration that early environment impacts on DRD4 and Novelty Seeking) are notable and herald a new era of personality genetics. Finally, consideration of the broader phenotypic expression of common polymorphisms (e.g. the 'social brain', altruism, etc.) and the use of new experimental paradigms including neurophysiological, neuropsychological and computer games that go beyond the narrow self-report questionnaire design will enable a deeper understanding of how common genetic polymorphisms modulate human behavior. Human personality, defined by Webster as the quality or state of being a person or the complex of characteristics that distinguishes an individual, surely requires a more encompassing view towards understanding its complex molecular genetic architecture.

Serotonin transporter function is an early step in left-right patterning in chick and frog embryos

The neurotransmitter serotonin has been shown to regulate a number of embryonic patterning events in addition to its crucial role in the nervous system. Here, we examine the role of two serotonin transporters, the plasma membrane serotonin transporter (SERT) and the vesicular monoamine transporter (VMAT), in embryonic left-right asymmetry. Pharmacological or genetic inhibitors of either SERT or VMAT specifically randomized the laterality of the heart and viscera in Xenopus embryos. This effect takes place during cleavage stages, and is upstream of the left-sided gene XNR-1. Targeted microinjection of an SERT-dominant negative construct confirmed the necessity for SERT function in embryonic laterality and revealed that the descendants of the right ventral blastomere are the most dependent upon SERT signaling in left-right patterning. Moreover, the importance of SERT and VMAT in laterality is conserved in chick embryos, being upstream of the early left-sided gene Shh. Endogenous transcripts of SERT and VMAT are expressed from the initiation of the primitive streak in chick and are asymmetrically expressed in Hensen's node. Taken together our data characterize two new right-sided markers in chick gastrulation, identify a novel, early component of the left-right pathway in two vertebrate species, and reveal a new biological role for serotonin transport.