Association between dopamine D4 receptor (D4DR) Exon III polymorphism and novelty seeking in Japanese subjects

Art Value Creation and Destruction

I present a theory of creative and destructive value state referring to abstract art. Value is a probabilistic state held as a mixture of its expectation and information forces that coexist in a give-and-take relationship. Expectations are driven by the disclosure of novel information about the value state of various events of desire. Each bit of accumulated information contributes to the improvement of perception up to a threshold level, beyond which begin conscious states. The desire to disclose a value state triggers a triadic system of evaluation which uses concepts, observables and approaches. While the triadic valuation mechanisms can be used to assess various commodities, the scope of this work is limited to the case of artworks, in particular abstract paintings. I assume that art value is basically mediated by the interplay between these value state mechanisms of creation and destruction. Expectations in artwork develop attraction by challenging its contemplator to evaluate (predict) its meaning. Once the relevant information, corresponding to its creative expectations, is acquired (and conditioned), emotional states of indifference, disinterest and desensitization develop.

Taking risks to feel excitement: Detailed personality profile and genetic associations

This study mapped the personality and genetics of risky excitement-seekers focusing on skydiving behavior. We compared 298 skydivers to 298 demographically matched controls across the NEO Personality Inventory-3 domains, facets, and 240 items. The most significant item-level effects were aggregated into a poly-item score of skydiving-associated personality markers (Study 1), where higher scores describe individuals who enjoy risky situations but have no self-control issues. The skydiving-associated personality marker score was associated with greater physical activity, higher rate of traumatic injuries, and better mental health in a sample of 3558 adults (Study 2). From genetic perspective, we associated skydiving behavior with 19 candidate variants that have previously been linked to excitement-seeking (Study 1). Polymorphisms in the SERT gene were the strongest predictors of skydiving, but the false discovery rate-adjusted (FDR-adjusted) p-values were non-significant. In Study 2, we predicted the skydiving-associated personality marker score and E5: Excitement-seeking from multiple risk-taking polygenic scores, using publicly available summary data from genome-wide association studies. While E5: Excitement-seeking was most strongly predicted by general risk tolerance and risky behaviors’ polygenic scores, the skydiving-associated personality marker score was most strongly associated with the adventurousness polygenic scores. Phenotypic and polygenic scores associations suggest that skydiving is a specific—perhaps more functional—form of excitement-seeking, which may nevertheless lead to physical injuries.

The adaptive value of personality differences revealed by small island population dynamics

Whether differences in personality among populations really exist and, if so, whether they are only due to cultural and linguistic differences or have a genetically selected adaptive value, is a controversial issue. In this research, we compared three Italian populations living on three small archipelagos in the Tyrrhenian Sea (n = 993), with their corresponding neighbouring mainlanders (n = 598), i.e. sharing the same geographical origin, culture and language. We used an adjective‐based Big Five questionnaire in order to measure personality traits in four categories of individuals for each archipelago/mainland population: (1) original islanders; (2) non‐original islanders; (3) mainlanders and (4) immigrants to the islands. We further analysed original and non‐original islanders who had or had not emigrated from the islands. We found that islanders had different personality traits from mainlanders, the former being more conscientious and emotionally stable and less extraverted and open to experience. We also found that the subgroup of islanders whose ancestors had inhabited their island for about 20 generations in isolation (original islanders, n = 624) were less extraverted and open to experience than immigrants (n = 193). In contrast, immigrants retained the typical personality profile of the mainland populations. Lastly, emigrants from the islands (n = 209) were significantly more extraverted and open to experience than original and non‐original islanders who had never left their island (n = 741). We hypothesise that population differences in extraversion and openness to experience are more probably related to genetic differences which evolved rapidly, presumably through an active gene flow produced by selective emigration from the islands. Copyright © 2006 John Wiley & Sons, Ltd.

The dopamine D2 receptor gene TaqI A polymorphism is not associated with Novelty Seeking, Harm Avoidance and Reward Dependence in healthy subjects

Allele A1 of the TaqI A restriction fragment length polymorphism (RFLP) of the dopamine D2 receptor gene has been found to be associated with substance abuse and alcoholism. The personality trait of Novelty Seeking (NS) is also associated with substance abuse and dependence. We hypothesised, on the basis of involvement of dopaminergic mechanisms in substance abuse, that the presence of allele A1 of the dopamine D2 receptor gene may represent a genetic predisposition for the NS personality trait. We investigated, therefore, whether the allele A1 of the TaqI A RFLP of the dopamine D2 receptor gene is associated with the NS dimension of the Tridimensional Personality Questionnaire (TPQ) in healthy Caucasian subjects with no history of alcohol or substance abuse or dependence. We genotyped 204 subjects aged 18 to 30 years. There was no association between any of the alleles of the D2 receptor genes and any of the TPQ scores (NS, Harm Avoidance, Reward Dependence). We conclude that allele A1 of the TaqI A RFLP of the dopamine D2 receptor is not associated with NS personality trait in healthy Caucasian subjects.

Associations Among Monoamine Neurotransmitter Pathways, Personality Traits, and Major Depressive Disorder

Major depressive disorder (MDD) is a complex psychiatric disease requiring multidisciplinary approaches to identify specific risk factors and establish more efficacious treatment strategies. Although the etiology and pathophysiology of MDD are not clear until these days, it is acknowledged that they are almost certainly multifactorial and comprehensive. Monoamine neurotransmitter system dysfunction and specific personality traits are independent risk factors for depression and suicide. These factors also demonstrate complex interactions that influence MDD pathogenesis and symptom expression. In this review, we assess these relationships with the aim of providing a reference for the development of precision medicine.

Candidate genes for novelty-seeking: a meta-analysis of association studies of DRD4 exon III and COMT Val158Met

OBJECTIVE

Two widely studied genetic polymorphisms in the dopaminergic system [DRD4 exon III variable number of tandem repeat (VNTR) and COMT Val158Met] have been reported to be associated with novelty-seeking, but the results have been highly inconsistent. Therefore, a meta-analysis of the associations between these two polymorphisms and novelty-seeking was conducted.

PARTICIPANTS AND METHODS

For DRD4, 24 studies comprising 27 samples and including 4933 participants were selected. Genotype grouping, sex, mean age, ethnicity, and sample characteristics were examined as moderators. For COMT, nine studies comprising 13 samples and including 2633 participants were selected. Sex, mean age, ethnicity, and sample characteristics were included as moderators. We also tested for possible publication bias.

RESULTS

The significant association between the DRD4 polymorphism and novelty-seeking was supported, but no association was found between the COMT polymorphism and novelty-seeking. In addition, our findings revealed that sex and age both directly moderate the relationship between DRD4 and novelty-seeking. Meanwhile, ethnicity can interact with age, sex, and genotype grouping, and age and sex can interact with each other, to moderate the association between the DRD4 exon III VNTR polymorphism and novelty-seeking.

CONCLUSION

Our results provide evidence of association between the DRD4 exon III VNTR polymorphism and novelty-seeking, which is inconsistent with the results of previous meta-analysis. Furthermore, several direct and indirect moderators are also identified to explain contradictory results in the existing literature. However, our results regarding COMT are consistent with those of previous meta-analysis.

The association between the serotonin and dopamine neurotransmitters and personality traits

Evidence from previous studies has reported that complex traits, including psychiatric disorders, are moderately to highly heritable. Moreover, it has also been shown that specific personality traits may increase the risk to develop mental illnesses. Therefore the focus of the research shifted towards the identification of the biological mechanisms underpinning these traits by exploring the effects of a constellation of genetic polymorphisms in healthy subjects. Indeed, studying the effect of genetic variants in normal personality provides a unique means for identifying candidate genes which may increase the risk for psychiatric disorders. In this review, we discuss the impact of two of the most frequently studied genetic polymorphisms on personality in healthy subjects, the 5-HTT polymorphism of the serotonin transporter and the DRD2/DRD4 polymorphisms of the D2/D4 dopamine's receptors. The main aims are: (a) to highlight that the study of candidate genes provides a fruitful ground for the identification of the biological underpinnings of personality without, though, reaching a general consensus about the strength of this relationship; and (b) to outline that the research in personality genetics should be expanded to provide a clearer picture of the heritability of personality traits.

Attention-Deficit/Hyperactivity Disorder: Focus upon Aberrant N-Methyl-D-Aspartate Receptors Systems

Attention-deficit/hyperactivity disorder (ADHD) pathophysiology persists in an obscure manner with complex interactions between symptoms, staging, interventions, genes, and environments. Only on the basis of increasing incidence of the disorder, the need for understanding is greater than ever. The notion of an imbalance between central inhibitory/excitatory neurotransmitters is considered to exert an essential role. In this chapter, we first review how the default mode network functions and dysfunction in individuals diagnosed with ADHD. We also present and briefly review some of the animal models used to examine the neurobiological aspects of ADHD. There is much evidence indicating that compounds/interventions that antagonize/block glutamic acid receptors and/or block the glutamate signal during the "brain growth spurt" or in the adult animal may induce functional and biomarker deficits. Additionally, we present evidence suggesting that animals treated with glutamate blockers at the period of the "brain growth spurt" fail to perform the exploratory activity, observed invariably with control mice, that is associated with introduction to a novel environment (the test cages). Later, when the control animals show less locomotor and rearing activity, i.e., interest in the test cages, the MK-801, ketamine and ethanol treated mice showed successively greater levels of locomotion and rearing (interest), i.e., they fail to "habituate" effectively, implying a cognitive dysfunction. These disturbances of glutamate signaling during a critical period of brain development may contribute to the ADHD pathophysiology. As a final addition, we have briefly identified new research venues in the interaction between ADHD, molecular studies, and personality research.

Association study on pathological gambling and polymorphisms of dopamine D1, D2, D3, and D4 receptor genes in a Korean population

Several studies have reported that some dopaminergic receptor polymorphisms are associated with pathological gambling (PG). Considering that there are major race and ethnic group difference in dopaminergic polymorphisms, the result of genetic association studies should be confirmed in more homogeneous population to avoid problems of population stratification. The present study aimed to investigate whether selected polymorphisms in the dopamine receptors genes (DRD1, DRD2, DRD3, and DRD4) are associated with PG in Korean population which is consisted of only Korean ancestry. Subjects were 104 men with a diagnosis of PG and 114 unrelated age-matched normal control men. Genotyping was performed for the DRD1 gene -48 A/G, DRD2 gene TaqI A, DRD3 gene Ser9Gly, and DRD4 gene exon III variable number tandem repeat polymorphisms. The method of multifactor dimensionality reduction (MDR) was used to analyze gene-gene interactions. There were no differences in the frequencies of any studied polymorphisms between patients with PG and normal controls. MDR analysis did not show a significant effect of the 4 dopamine receptor gene polymorphisms on susceptibility to PG (P > 0.05). The present study suggests that the analyzed polymorphisms of the dopamine receptor genes might not be associated with PG in a Korean population.

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.

The interaction between serotonin receptor 2A and catechol-O-methyltransferase gene polymorphisms is associated with the novelty-seeking subscale impulsiveness

OBJECTIVE

Novelty seeking is a trait that has been consistently associated with problem behaviours. There is evidence for heritability of novelty seeking, but the molecular genetic basis of the trait is still widely unclear.

METHODS

The interaction between polymorphisms of catechol-O-methyltransferase (COMT) and serotonin receptor 2A genes was examined in relation to novelty seeking and its different subscales in healthy Finnish adults. A subsample of 1214 participants derived from a population-based sample was genotyped for the COMT Val158Met (rs4680) and HTR2A T102C (rs6313) genes. Novelty seeking was measured twice, with a 4-year interval, using Cloninger's Temperament and Character Inventory.

RESULTS

The interaction between COMT Val158Met and HTR2A T102C polymorphisms was found to be associated with subscale impulsiveness. T/T carriers of HTR2A T102C polymorphism, that also had Met/Met genotype of COMT Val158Met single nucleotide polymorphism, scored significantly higher on impulsiveness than Val allele carriers (P=0.005).

CONCLUSION

Our results suggest that the interaction between dopaminergic and serotonergic genes might underlie impulsiveness. Together with earlier research our results also stress the importance of considering novelty seeking as a heterogeneous trait with its subscales having different genetic backgrounds.

Association of VNTR polymorphisms in the MAOA promoter and DRD4 exon 3 with heroin dependence in male Chinese addicts

OBJECTIVE

To explore the involvement of variable number tandem repeat (VNTR) polymorphisms in the monoamine oxidase A (MAOA) promoter and exon 3 of the dopamine D4 receptor (DRD4) gene in heroin addiction modulate the vulnerability of individuals to heroin addiction.

METHODS

Eight hundred and ninety-four male heroin addicts without other psychiatric disorders, were recruited as subjects. Another community 180 males were selected randomly as controls.

RESULTS

The geno-distribution of the DRD4 exon 3 VNTR polymorphism in controls was in Hardy-Weinberg equilibrium (HWEchi(2)=0.925), but the distribution in heroin addicts was not (HWEchi(2)=28.35). The long-repeat alleles of the DRD4 exon 3 VNTR polymorphism were found more frequently in the heroin addicts (P=0.019). However, the long-repeat alleles of the MAOA promoter VNTR polymorphism were not (P=0.828). No interaction between these two VNTR polymorphisms was found by using multiple logistic regression analysis (P=0.261).

CONCLUSION

The long-repeat allelic variants (>4-repeats) and 2-repeat allele of the DRD4 exon 3 VNTR polymorphism might be risk alleles for individual vulnerability to heroin addiction in Chinese men, but the MAOA promoter VNTR polymorphism does not mean that the partial dominant inherited mode might involved in the genetics of heroin dependence.

Dopamine and serotonin systems modify environmental effects on human behavior: a review

The relative influences of genetic and environmental factors in the development of human behavior have been a long-term topic for an intense debate. Recent behavioral genetic studies suggest focusing on the joint effect of genes and environment, and especially on the life-course developmental interplay between nature and nurture. Vulnerability to environmental adversities and sensitivity to its benefits may be conditional on genetic background, and regarding psychological outcomes, these kinds of gene x environment interactions may be of higher importance than direct gene-trait associations. In our recent series of studies, we have shown that different variants of serotonergic and dopaminergic genes may moderate the influence of environmental conditions on a range of psychological outcomes, i.e. temperament, depression, hostility, and educational attainment. These studies suggest that depending on their genotype, people may be differentially sensitive to the environmental conditions they encounter. In the light of these results it seems highly plausible that the effects of genes may become evident only when studied in the context of environmental factors.

Minor genetic variants of the dopamine D4 receptor (DRD4) polymorphism are associated with novelty seeking in healthy Japanese subjects

Although an association between the dopamine receptor D4 (DRD4) gene and personality traits had been previously investigated, results from previous studies were not conclusive. This may be due to the method of grouping used, which categorized the gene population into two groups based on the length of the variable number of tandem repeats (VNTR) in exon 3. In the present study, we categorized 616 healthy Japanese subjects into more than two groups by further subdividing the DRD4 48-bp VNTR polymorphism, and compared Temperament and Character Inventory (TCI) scores among the groups. A significant difference was found between the DRD4 48-bp VNTR polymorphism and novelty seeking (p=0.016). The novelty-seeking scores in the subjects carrying the 5/5 genotype were significantly higher than in those carrying the 2/2 genotype (p=0.002) or the 4/4 genotype (p=0.005). However, when the conventional method of grouping was used (i.e., short alleles vs. long alleles), there were no significant associations between the DRD4 VNTR polymorphism and any TCI scores. Our results suggest that minor 5-repeat allele is associated with high novelty-seeking scores in healthy Japanese subjects.

Association between Dopamine D4 Receptor Gene Polymorphism and Scores on a Continuous Performance Test in Korean Children with Attention Deficit Hyperactivity Disorder

OBJECTIVE

The aim of this study was to evaluate the association between a variable number of tandem repeats polymorphism at the dopamine D4 receptor gene (DRD4) and the performance of children with attention deficit hyperactivity disorder (ADHD) in a continuous performance test (CPT).

METHODS

This study included 72 ADHD children (mean age=9.39+/-2.05 years) who were recruited from one child psychiatric clinic. The omission errors, commission errors, reaction time and reaction standardization in the CPT were computed. The number of 48-base pairs tandem repeats in the exon III of DRD4 was analyzed in a blind manner.

RESULTS

The homozygosity of the 4-repeat allele at DRD4 was significantly associated with fewer commission errors (t=2.364, df=28.685, p=0.025) and standard deviation of reaction time (t=2.351, df=24.648, p=0.027) even after adjusting for age. The results of analyses of CPT measured values among three groups showed that the group with higher frequency of the 4-repeat allele showed a lower mean score of commission errors (F=4.268, df=2, p=0.018).

CONCLUSION

These results suggest a protective role of 4-repeat allele of the DRD4 polymorphisms on commission errors in the CPT in children with ADHD.

DRD2 C32806T modifies the effect of child-rearing environment on adulthood novelty seeking

Preliminary evidence suggests that there may be longitudinal interactions between environmental and genetic factors in predicting Novelty seeking. We have previously found in small and selected subsample from the Cardiovascular Risk in Young Finns study, that an association between the polymorphism of dopamine receptor D4 was moderated by the childhood environment, as indexed by hostile maternal child-rearing. We wanted to replicate this finding in a population based sample of 1,114 men and women using another candidate gene of dopaminergic system, that is, the dopamine receptor D2 (DRD2). The child-rearing environment of the participants was assessed by their mothers when the participants were children or adolescents, and adulthood Novelty seeking was self-rated by the participants 17 and 21 years later at the ages of 24-39. Genotyping of DRD2 C32806T (rs 1800497) was performed using TaqMan 5'nuclease assay. DRD2 was not directly associated with Novelty seeking, but there was a significant DRD2 x strict maternal disciplinary style interaction in predicting Novelty seeking (F = 7.08, P = 0.008). The interaction showed that when the child-rearing environment was punitive, participants carrying any A1 allele of the DRD2 gene had higher scores on Novelty seeking than carriers of the A2/A2 genotype. The genotype had no effect on Novelty seeking when the childhood environment was more favorable. The findings suggest that the DRD2 may have an environmentally moderated impact on Novelty seeking and that the origins of such an association may lie already in childhood.

Evidence for a gene-gene interaction in predicting children's behavior problems: association of serotonin transporter short and dopamine receptor D4 long genotypes with internalizing and externalizing behaviors in typically developing 7-year-olds

Recent work on the molecular genetics of complex traits in typical and atypical human development has focused primarily on associations of single genes with behavior. Disparate literature suggests that the presence of one or two copies of the short allele of the serotonin transporter (5-HTT) gene and the long allele (7-repeat allele) version of the dopamine receptor D4 (DRD4) gene predicts internalizing- and externalizing-related behaviors, respectively. Apparently for the first time in the extant literature, we report a gene-gene statistical interaction on behavior problems in a group of typically developing children at age 7. DNA was extracted from buccal cells collected from 108 children and genotyped for short and long alleles of the 5-HTT gene and the short (2-5 repeats) versus long (6-8 repeats) allele of the DRD4 gene. Mothers completed the Child Behavior Checklist. As predicted, children with one or two copies of the short allele of the 5-HTT gene and the long allele version of the DRD4 gene exhibited significantly more internalizing and externalizing behaviors at age 7 than children with other combinations of the 5-HTT and DRD4 short and long genotypes. As well, children with the 5-HTT long and DRD4 long genotypes had the lowest reported scores on internalizing and externalizing behaviors at age 7, suggesting that the presence of the 5-HTT long genotype may serve as a protective factor against these behaviors in children with the long DRD4 genotype. Implications of these findings for understanding cumulative biological risk and protective factors in childhood behavior problems and psychopathology are discussed.

Association of the dopamine D4 receptor (DRD4) gene and approach-related personality traits: meta-analysis and new data

BACKGROUND

Two variants in the dopamine D4 receptor (DRD4) gene have been reported to be associated with human approach-related traits such as novelty seeking and extraversion. However, the strength of evidence for this association remains uncertain.

METHODS

We conducted a meta-analysis of published studies of the association between the DRD4 gene variable number of tandem repeats (VNTR) and C-521T polymorphisms and human approach-related personality traits, including novelty seeking, extraversion, and impulsivity, restricted to adult samples recruited from nonpsychiatric populations, and extended on this literature by attempting to confirm any evidence of association in a replication sample (n = 309) selected for extreme scores on the extraversion subscale of the Eysenck Personality Questionnaire from a large (n = 40,090) population-based sample.

RESULTS

Our initial meta-analysis supported the association of the DRD4 C-521T polymorphism, but not the VNTR polymorphism, with approach-related traits. This conclusion was qualified by evidence of significant publication bias and the failure to detect association in a replication sample comprising individuals at the extremes of the trait distribution. The association of the C-521T polymorphism observed in our initial meta-analysis was robust to the inclusion of these new data, but our revised meta-analysis indicated that the association was present for measures of novelty seeking and impulsivity but not for measures of extraversion.

CONCLUSIONS

The DRD4 gene may be associated with measures of novelty seeking and impulsivity but not extraversion. The association of the C-521T variant with these measures, if genuine, may account for up to 3% of phenotypic variance.

Gene-environment contributions to young adult sexual partnering

To date, there has been relatively little work on gene-environment contributions to human sexuality, especially molecular analyses examining the potential contributions of specific polymorphisms in conjunction with life experiences. Using Wave III data from 717 heterozygous young adult sibling pairs included in the National Longitudinal Study of Adolescent Health, this article examined the combined contributions of attendance at religious services and three genetic polymorphisms (in the dopamine D4 receptor [DRD4]), dopamine D2 receptor [DRD2]), and the serotonin transporter promoter [5HTT]) to sensation seeking, a personality construct related to sexual behavior, and the number of vaginal sex partners participants had in the year before interview. Data analyses used an Allison mixed model approach to account for population stratification and correlated observations. DRD4 was unrelated to sensation seeking and to the number of sex partners in tests of both main effects and in interaction with religious attendance. Contrary to hypothesis, presence of the A1 DRD2 allele was associated with having had fewer sex partners in the past year. Associations between the 5HTT allele and sex partners varied by religious attendance, but again the patterns of associations were contrary to hypothesized relationships and were small in magnitude. These findings underscore the necessity of using more comprehensive multiple gene-multiple life experience approaches to investigations of complex behaviors such as sexual patterns.

Novelty seeking and the dopamine D4 receptor gene (DRD4) revisited in Asians: haplotype characterization and relevance of the 2-repeat allele

The relationship of the dopamine D4 receptor gene (DRD4) to the behavioral trait of novelty seeking has not been uniformly consistent. A methodological shortcoming in previous studies may relate to the way different DRD4 variants were categorized. Because of evolutionary and functional (e.g., diminished potency to reduce cAMP) similarities between the 2- and 7-repeat (2R, 7R) alleles of the DRD4, we suggest grouping of these two alleles together may facilitate detection of biologically meaningful and reproducible association findings with behavioral traits. We measured novelty seeking with the Tridimensional Personality Questionnaire (TPQ) in a community sample of Caucasian, Korean, and Filipino subjects (N = 171) who were subsequently characterized for the DRD4 variable number of tandem repeats (VNTR). In the Korean sample, those with a 2R and/or 7R allele scored significantly higher on novelty seeking scale (P < 0.05). By contrast, grouping the VNTR alleles by size (2, 3, 4 vs. 5, 6, 7), as has been done in similar studies of Asian subjects, was not significant. Using the extreme discordant phenotype (EDP) strategy in the pooled sample and selecting the individuals within the upper and lower decile, we observed a trend for association with higher novelty seeking in individuals who carry the 2R and/or 7R alleles (P = 0.06). We also confirmed that the 2R allele in the Korean and Filipino subjects was the result of a one-step recombination event between the 4R and 7R alleles. This study suggests that genetic association analyses can benefit by consideration of the shared functional and evolutionary attributes of the DRD4 2R and 7R alleles.

The association of DRD4 and novelty seeking is found in a nonhuman primate model

OBJECTIVE

The association of novelty seeking with a repeat polymorphism in the coding region of the dopamine D4 receptor gene (DRD4) has been demonstrated in several human populations, but not in others. The objective of this study was to test the generality of the association in a captive nonhuman primate population of known history, using objective methods for assessing novelty seeking and a pedigree-based association design.

METHODS

Four hundred and fifty two socially-living vervet monkeys (Cercopithecus aethiops) from a large multigenerational pedigree at the UCLA-VA Vervet Research Colony were studied. Two variants in the 48 base pair repeat in exon III of the DRD4 gene have been found in this population, a six-repeat (92%) and a less common five-repeat (8%). Novelty seeking was measured by the latency to approach a large and potentially threatening novel object placed in the home enclosure. Heritability of novelty seeking and the association of novelty seeking with the DRD4 polymorphism were assessed using variance component modeling as implemented in Sequential Oligogenic Linkage Analysis Routines.

RESULTS

The variance component analysis indicated that the DRD4 variant explained a significant portion of the total variance in novelty seeking. The final model included a significant effect of the DRD4 polymorphism (P=0.03), which explained 13% of the phenotypic variance, and a significant remaining genetic effect (h=0. 467+/-0.095, P<0.0001).

CONCLUSIONS

The association of DRD4 with novelty seeking has now been replicated in a nonhuman primate species, the vervet monkey.

Genetic variation in the dopamine D4 receptor (DRD4) gene and smoking cessation: follow-up of a randomised clinical trial of transdermal nicotine patch

Smokers of European ancestry (n=720) who participated in a double-blind, randomised, placebo-controlled trial of transdermal nicotine replacement therapy, were genotyped for two functional polymorphisms (variable number of tandem repeats (VNTR) and a C to T transition at position -521 (C-521T)) in the dopamine D4 receptor gene (DRD4) gene. Logistic regression models of abstinence at 12- and 26-week follow-ups were carried out separately for each polymorphism. For the DRD4 VNTR models, the main effect of treatment was significant at both 12-week (P=0.001) and 26-week (P=0.006) follow-ups, indicating an increased likelihood of successful cessation on active nicotine replacement therapy transdermal patch relative to placebo. The main effect of DRD4 VNTR genotype was associated with abstinence at 12-week follow-up (P=0.034), with possession of one or more copies of the long allele associated with reduced likelihood of cessation (17 vs 23%), but this effect was not observed at 26-week follow-up. For the DRD4 C-521T models, no main effect or interaction terms involving genotype were retained in the models at either 12- or 26-week follow-up. These data are consistent with observations from studies of the DRD2 gene that genetic variants related to relatively decreased dopaminergic tone in the mesocorticolimbic system are associated with increased risk for relapse to smoking following a cessation attempt.

Lack of association between polymorphisms of the dopamine receptor D4 and dopamine transporter genes and personality traits in a Korean population

Human personality traits have a considerable genetic component. Cloninger et al. were the first to postulate that certain personality traits, such as novelty seeking, are related to the dopamine neurotransmitter system. In this study, we investigated the associations between dopamine receptor D4 (DRD4) exon III and dopamine transporter (DAT1) polymorphisms and personality traits. The DRD4 and DAT1 gene polymorphisms were genotyped in 214 healthy Korean subjects, whose personality traits were assessed with the Temperament and Character Inventory (TCI). There were no significant differences between scores of TCI temperament dimensions (novelty seeking, harm avoidance, reward dependence, and persistence) and DRD4 gene polymorphism. The DAT1 gene polymorphisms also showed no significant association with any of the temperament subscales of the TCI. These data suggest that DRD4 and DAT1 gene polymorphism may not associated with personality traits in a Korean population.

Personality, dopamine receptor D4 exon III polymorphisms, and academic achievement in medical students

This study investigated the relationships between genetic polymorphisms, personality traits, and academic achievement in medical school students. Study subjects were 220 1st-year medical students at Korea University Medical School during two consecutive academic years (2003-2004). Grade-point averages (GPA) during the second semester of the 1st year of the medical school were obtained as a measure of academic achievement. In addition, all participants completed the Temperament and Character Inventory and questionnaires on depression and anxiety. The polymorphisms in exon III of the dopamine D4 receptor (DRD4) were determined using the polymerase chain reaction. Our results revealed that both male and female subjects with a higher GPA may be characterized as having higher persistence and lower novelty seeking traits. In addition, male subjects with high GPA had higher scores in self directedness and female subjects with a higher GPA may be characterized as having higher scores in harm avoidance. Male students with 4-repeat alleles had a significantly lower GPA than male students without 4-repeat alleles. This relationship also remained after controlling for the personality variables, none of which showed a relationship with the polymorphism after Bonferroni correction. For females, however, no associations could be found between GPA and the polymorphism. Thus, the present study demonstrated for the first time a possible influence of the DRD4 48 bp variable number of tandem repeats polymorphism on academic achievement and proved that this was not mediated by performance-associated personality traits.

Dopamine D4 receptor gene and the −521C>T polymorphism of the upstream region of the dopamine D4 receptor gene in schizophrenia

OBJECTIVE

The dopamine D4 receptor (DRD4) is a candidate gene for increasing genetic susceptibility to schizophrenia. A recent study found that a -521C>T promoter base pair change affects transcriptional regulation of the DRD4 gene. The present study was designed to investigate the role of both the -521C>T single nucleotide polymorphism and the DRD4 variable number tandem repeat (VNTR) polymorphism.

METHODS

A case-control study of 630 Chinese schizophrenic patients and 428 Chinese controls was conducted to test for allelic association with schizophrenia.

RESULTS

The number of DRD4 VNTR fragments was associated with schizophrenia. Long DRD4 VNTR fragments as opposed to short fragments were commoner in schizophrenia. No evidence was found for allelic association between the -521C>T DRD4 polymorphism and schizophrenia.

CONCLUSIONS

This study provides preliminary and unconfirmed evidence for the involvement of the DRD4 repeat VNTR in the pathogenesis of schizophrenia.

Association between dopamine D4 receptor (DRD4) exon III polymorphism and Neuroticism in the Japanese population

The association between the dopamine D4 receptor (DRD4) exon III polymorphism and personality trait of novelty seeking (NS) has been studied intensively. In the Japanese population, the results of the previous studies did not always coincide. In the present study, we investigated the association between the polymorphism and personality traits evaluated by using the Revised NEO Personality Inventory (NEO PI-R) and State-Trait Anxiety Inventory (STAI) in 196 Japanese subjects. A meta-analysis of the present and previous Japanese studies was also conducted regarding NS. As a result, significant association was observed between the polymorphism and personality traits evaluated by using NEO PI-R as a whole (p=0.022, MANCOVA). Subsequent analyses showed a significant association between short alleles (2-4 repeats) and higher scores for Neuroticism or its subscales, Anxiety, Depression, and Vulnerability (p=0.015, 0.039, 0.021, and 0.008, respectively, uncorrected). No other significant difference in the scores for NEO PI-R was observed in the subsequent analyses. Significant association was also observed between the polymorphism and scores for STAI as a whole (p=0.004, MANCOVA). Subsequent analyses did not show significant association, although a weak trend for the relation between the genotype consisting of short alleles and Trait Anxiety was observed (p=0.10, uncorrected). The meta-analysis showed no significant association between the polymorphism and NS. Thus, the present study suggested the association between the short allele of the DRD4 exon III polymorphism and personality trait of Neuroticism in Japanese subjects.

Serotonin transporter polymorphisms affect human blood glucose control

We measured the effect of nutritional intervention on clinical data, including fasting blood glucose (FBG), and their association with polymorphisms of the serotonin transporter-linked polymorphic region (5-HTTLPR) which might affect adherence. Enrolled in the intervention program were 264 Japanese women not on medication for diabetes, hypercholesterolemia or hypertension. The 5-HTTLPR allele (S and L) frequencies among the subjects differed markedly from those of Caucasians: SS (n = 183), LS (n = 69), and LL (n = 12). The decrease in FBG (DeltaFBG) from the beginning to the end of the program (11 weeks; short-term study), and DeltaFBG from the beginning to a follow-up check performed between 2002 and 2004 (average of 23 years later; long-term study) was calculated. The SS homozygotes of 5-HTTLPR showed larger DeltaFBG (P = 0.01 and P < 0.0001 in the short- and long-term studies, respectively) than DeltaFBG with other genotypes.

Cloninger's temperament dimensions and epidermal growth factor A61G polymorphism in Finnish adults

This study examines a link between human temperament and epidermal growth factor (EGF). There is evidence that dopaminergic neurotransmission in the central nervous system has a role in temperament, especially in novelty seeking. Functional polymorphism in EGF gene has an impact on EGF production, and EGF, in turn, appears to affect the development of midbrain dopaminergic neurons. Epidermal growth factor gene A61G polymorphisms were studied in a randomly selected sample of 292 Finnish adults. Their temperaments were assessed twice (with a 4-year test-retest interval) with Cloninger's Temperament and Character Inventory consisting of four dimensions, i.e. novelty seeking (NS), harm avoidance (HA), reward dependence (RD) and persistence (P). The findings on men showed a significant association between a presence of the G/G polymorphism and scoring in the highest tertile on NS in both test and retest. The same was true with men who scored high on RD, especially on sensitivity, in both tests. Among women, G/G polymorphism was associated with a stable high level of P. Importantly, temperament dimensions, as assessed with one test only, did not provide replicable associations with EGF polymorphism across the two measurements. Our results demonstrate the importance of reliable phenotype assessment and lend support to the hypothesis that dopaminergic activity is one factor underlying stable temperament.

Novelty seeking: interaction between parental alcohol use and dopamine D4 receptor gene exon III polymorphism over 17 years

Recent meta-analyses have questioned the association between the dopamine receptor D4 (DRD4) gene polymorphism and the temperament trait of novelty seeking, and proposed an interaction between the polymorphism and other factors. We wanted to test whether parental alcohol use during childhood moderated the effect of an offspring dopamine receptor gene (DRD4) polymorphism on the temperament trait of novelty seeking in adulthood. A population-based sample of children and adolescents (n=2149) and their parents was examined in 1980 and 1983 on parental alcohol use and rearing practices. In 1997, study participants completed the Temperament and Character Inventory for the novelty-seeking temperament trait, and a subsample (n=150) was genotyped for the DRD4 exon III polymorphism. For the participants with the father, but not the mother, reporting more frequent alcohol consumption or drunkenness in examinations 17 and/or 14 years before the novelty-seeking assessment, an association between the short (two- or five-repeat) alleles of the DRD4 gene and extremely high novelty-seeking scores was observed. When the father reported less frequent alcohol consumption or drunkenness, the genotype was not associated with novelty seeking. The association remained after controlling for sex, age, and maternal child-rearing. These results provide preliminary information on gene-environment interaction on the temperament trait of novelty seeking and may partly explain the heterogeneity of findings concerning the association between DRD4 polymorphisms and novelty seeking.

Relationship between DRD4 polymorphism and lipid metabolism: what is the role of novelty seeking?

OBJECTIVE

This study examined the association of the dopamine receptor D4 (DRD4) gene polymorphism with the temperament dimension of novelty seeking (NS) on cardiovascular heart disease risk factors [the levels of high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, and triglycerides].

METHOD

From the ongoing population-based study of 'Cardiovascular Risk in Young Finns', 125 participants were DRD4 genotyped in 1997 and responded to the NS scale of the Temperament and Character Inventory in 2001. Their cholesterol and triglyceride concentrations were assessed in 2001.

RESULTS

Having a 2- or 5-allele DRD4 polymorphism was related to high HDL cholesterol levels in men, but to low HDL cholesterol levels in women. NS was related to triglycerides in men and to LDL in women, but this was mediated by behavioral, age, and weight factors, and NS was not the underlying factor for the association between the polymorphism and lipids.

CONCLUSION

Our preliminary findings suggest that there is a link between the dopaminergic receptor gene DRD4 and lipid metabolism, but this link is dependent on gender.

Genetic variants implicated in personality: a review of the more promising candidates

Alleles of the serotonin transporter gene (SERT) and the dopamine 4 receptor gene (DRD4) were first associated with anxiety-related and novelty-seeking personality traits, respectively, in 1996. These early successes precipitated a flood of research into the genetic basis of personality; a quest that has yet to yield decisive answers. Here, both the theoretical and the empirical evidence implicating specific loci-in particular SERT and DRD4-in the development of personality is evaluated. Despite a paucity of statistically significant results following post-hoc analysis, and an excess of positive results derived from studies with small sample sizes, the existence of a genuine effect is argued for: a gene-personality relationship rendered periodically latent through genetic epistasis, gene-environment interactions, variation in genetic background, and the presence of other confounding variables.

Nature and nurture in novelty seeking

A sample of children (n=92), derived from a representative population sample of healthy young Finns (n=2149), was studied from childhood to adulthood over 14 years to determine whether the childhood environment moderated the effect of dopamine receptor gene (DRD4) polymorphism on novelty seeking (NS). A significant interaction between the DRD4 alleles and environmental variables was observed. When the childhood-rearing environment was more hostile (emotionally distant, low tolerance of the child's normal activity, and strict discipline), the participants carrying any two- or five-repeat alleles of the DRD4 gene had a significantly greater risk of exhibiting NS scores that were above the 10th percentile on a population distribution of 2149 adult Finnish women and men. The genotype had no effects on NS when the childhood environment was more favorable. Although the results are preliminary, pending replication, they nevertheless provide important information on the long-term effects of nurture and nature on NS temperament.

Effects of dopamine receptor D4 variation on alcohol and tobacco use and on novelty seeking: multivariate linkage and association analysis

The dopamine D4 receptor gene contains a polymorphic sequence consisting of a variable number of 48-base-pair (bp) repeats, and there have been a number of reports that this polymorphism is associated with variation in novelty seeking or in substance abuse and addictive behaviors. In this study we have assessed the linkage and association of DRD4 genotype with novelty seeking, alcohol use, and smoking in a sample of 377 dizygotic twin pairs and 15 single twins recruited from the Australian Twin Registry (ATR). We found no evidence of linkage or association of the DRD4 locus with any of the phenotypes. We made use of repeated measures for some phenotypes to increase power by multivariate genetic analysis, but allelic effects were still non-significant. Specifically, it has been suggested that the DRD4 7-repeat allele is associated with increased novelty seeking in males but we found no evidence for this, despite considerable power to do so. We conclude that DRD4 variation does not have an effect on use of alcohol and the problems that arise from it, on smoking, or on novelty seeking behavior.

Why do some individuals develop social phobia? A review with emphasis on the neurobiological influences

Social phobia, or social anxiety disorder, is now considered the most common anxiety disorder. Still, the etiology of the disorder is to an essential degree unknown. This paper presents an overview of various pathways to be considered in relation to the development of social phobia. The literature concerning genetics and family aggregation, behavioral inhibition, various forms of the learning account, and neurobiological influences was examined. The reviewed studies suggest that social phobia has a neuroanatomical basis in a highly sensitive fear network centered in the amygdaloid-hippocampal region, i.e. "the alarm system" of the brain, and encompassing the prefrontal cortex. This pattern is congruent with genetic studies proposing that the genetic component comprises a general vulnerability to fearfulness rather than to social phobia itself. Further, both family and twin studies support a hereditary contribution to social phobia resulting from genetic and environmental factors, which most likely operate in an interactive way rather than acting in isolation.

Genetics of personality: are we making progress?

For centuries, scientists are intrigued by the differences in personality between individuals. As early as in the ancient Greek civilization, people tried to formulate theories to systematize this diversity. With the increased interest in behavior genetics, personality was also considered a challenging phenotype. From the early start, studies suggested a heritable component in personality. After the successes of molecular genetic studies in unraveling the genetic basis of (mostly) monogenic diseases, the focus shifted towards complex traits, including psychiatric disorders. It was observed in several studies that personality measures differed between patients with psychiatric disorders and healthy controls. Therefore, normal personality was considered a viable endophenotype in the search for genes involved in psychiatric disorders such as affective disorders, ADHD and substance dependence. Genes that were to be found in studies on personality could be candidate genes for particular psychiatric disorders. In the course of time, however the study of genes for personality turned out to be at least as hard as the search for genes involved in other complex disorders. In this review, past studies, present problems and future directions concerning the study of personality genetics are discussed.

D2 and D4 dopamine receptor gene polymorphisms and personality traits in a young Korean population

The correlation between the D4 dopamine receptor gene (DRD4) and the D2 dopamine receptor gene (DRD2) polymorphisms was investigated with personality traits. For this study, homogeneous population consisting of 243 young alcohol- and drug-naive Koreans who were blood-unrelated with a mean age (+/-SD) of 13.87 (+/-0.30) years old was analyzed for the DRD4 and the DRD2 polymorphisms with their personality trait by Temperament and character inventory (TCI). The association between Novelty seeking (NS) score and DRD4 long alleles was only observed among the female subjects (t = 2.11, P = 0.037), but not in the male counter part. Female subjects who carried the DRD2 less frequent alleles (TaqI A1, TaqI B1, and Intron6 1) showed higher RD4 scores (dependence vs. independence) of Reward dependence (RD) than those without these alleles (P < 0.05). There was no interaction between DRD4 and DRD2 on the personality traits. These results, thus, confirmed the previous findings in which the long repeats of the DRD4-exon III polymorphism are related to NS personality trait, and also suggested that the DRD2 less frequent alleles were also associated with the reward-dependent trait.

Association between the type 4 dopamine receptor gene polymorphism and novelty seeking

OBJECTIVE

Mixed results have been reported on the association between the type 4 dopamine receptor gene (DRD4) and the temperament dimension of novelty seeking. We tested this association by specifying the analysis to components of novelty seeking.

METHODS

Participants were 150 high and low novelty-seeking scorers (the highest and lowest 10%) from a randomized, population-based sample of Finnish citizens in six age cohorts. We genotyped a 48-bp repeat polymorphism in the DRD4 gene. Novelty seeking was assessed by the Temperament and Character Inventory.

RESULTS

No difference in overall novelty seeking between individuals with no seven-repeat allele (short) and any seven-repeat allele (long), between the 4,4 and 4,7 genotype groups, and between long (l/l and s/l) and short (s/s) polymorphism groups were found. The odds ratio for high overall novelty seeking in the presence of any two- or five-repeated alleles vs. none was 2.41 (95% CI, 1.11-5.20). Corresponding odds ratios were significant for exploratory excitability (2.94; 95% CI, 1.32-6.59) and impulsiveness (2.74; 95% CI, 1.23-6.11) but not for other components of novelty seeking. No interactions with age or gender were detected.

CONCLUSIONS

The present study confirmed previous findings on the association between the type 4 dopamine receptor gene and novelty seeking, in particular exploratory excitability and impulsiveness. The tendency to avoid or approach a novel situation is a core concept of several temperamental theories. The present findings support the hypothesis that this tendency is associated with DRD4 and might concern temperament psychology in general, not only the concept of novelty seeking.

Genetic polymorphisms and personality in healthy adults: a systematic review and meta-analysis

A meta-analysis was conducted on studies reporting data on associations between candidate genes and human personality. Studies reporting data for psychiatric populations (including organic disease and substance abuse) were excluded. A total of 46 studies contributed to the analysis. Pooled data using a fixed-effects model suggested significant associations between the 5HTT LPR, DRD4 c>t, DRD4 length, DRD2 A1/A2, DRD3 A1/A2 polymorphisms and personality traits. A multivariate analysis using a mixed-effects model and including age, sex and predominant ethnicity as covariates was applied to the analyses of 5HTT LPR and DRD4 length polymorphism data. Only the association between the 5HTT LPR polymorphism and avoidance traits remained significant (P=0.038). However, sensitivity analyses excluding data from studies reporting allele frequencies not in Hardy-Weinberg equilibrium and unpublished data resulted in this association no longer being significant. Implications for the design of future association studies of human personality are discussed, including the likely sample sizes that will be required to achieve sufficient power and the potential role of moderating variables such as sex.

Allelic variants interaction of dopamine receptor D4 polymorphism correlate with personality traits in young Korean female population

Polymorphism in exon III of the dopamine D4 receptor (DRD4) gene has been implicated to be associated with the human personality trait of novelty seeking (NS). For this study, we have investigated the possible association between 48-bp VNTR in exon III and -521 C/T SNP of the DRD4 and personality traits among young ( approximately 14 years of age) Korean female population. We found that the interaction between the two alleles of DRD4 polymorphism, 48-bp VNTR and -521 C/T, were significantly high on NS (F = 4.88, P = 0.029) and persistence (P) (F = 5.05, P = 0.027) personality scores, suggesting that the variants of DRD4 gene influence the NS and P (persistent) personality traits. When analyzed independently, however, the two different alleles of DRD4 polymorphisms, 48-bp VNTR and -521 C/T, there was no direct correlation with the personality traits.

Temperament and character of Japanese eating disorder patients

Previous studies consistently reported a link between bulimic behaviors and high Novelty Seeking (NS), as measured by the Temperament and Character Inventory (TCI). However, it remains unclear whether this relationship is universal and occurs in different environments. Subjects of the present study consisted of 66 patients with anorexia nervosa restricting type (AN-R), 59 patients with anorexia nervosa binge eating/ purging type (AN-BP), 101 patients with bulimia nervosa purging type (BN), and 75 controls. NS score in AN-R patients was significantly lower than that in controls, although NS in BN patients did not differ from that in controls. The temperament of AN-R patients seems to be universal, even in different environments. Conversely, something other than temperament might be important in the development of bulimia nervosa in Japan.

A meta-analysis of the association between DRD4 polymorphism and novelty seeking

A meta-analytical review of 20 studies (n = 3907) of the association between DRD4 polymorphism and novelty seeking suggests the following conclusions: (a) on average, there is no association between DRD4 polymorphism and novelty seeking (average d = 0.06 with 95% CI of +/- 0.09), where 13 reports suggest that the presence of longer alleles is associated with higher novelty seeking scores and seven reports suggest the opposite; (b) there is a true heterogeneity among the studies (ie, unknown moderators do exist) but the strength of the association between DRD4 polymorphism and novelty seeking in the presence of any (unknown) moderator is likely to be weak; (c) search for moderators has not yielded any reliable explanation for the variability among studies. We propose that to find such moderators, theory-driven research for potential interaction, coupled with larger sample sizes should be employed. The growing availability of powerful statistical techniques, high-throughput genotyping and large numbers of polymorphic markers such as single nucleotide polymorphisms makes such proposed studies increasingly feasible.

Toward a molecular architecture of personality

Epidemiological studies provided a large body of evidence that personality dimensions are influenced by genetic factors and that the genetic component is highly complex, polygenic, and epistatic. However, consistent findings on the genetic basis of personality have yet remained sparse. In recent years, molecular genetics has begun to identify specific genes coding in particular for components of the serotonergic and dopaminergic neurotransmitter systems representing quantitative trait loci (QTLs) for behavioral traits. The QTL concept suggests that complex traits are not attributable to single genes. According to this polygenic model, the genetic basis of personality and behavior and its pathological variations thus results from additive or nonadditive interactions of various genes. As the number of suitable candidate genes constantly increases, the QTL model provides a reasonable explanation for the genetic basis of personality and its disorders. In this review, the current knowledge on the impact of a large number of candidate gene polymorphisms (e.g. variations in serotonin and dopamine receptor and serotonin transporter genes) on personality and temperament is summarized. Additionally, investigations of gene-gene and gene-environment interactions in humans and animals, which currently intensify the identification of genes that underlie behavioral variations, are examined. The findings converge on the notion that a probabilistic rather than deterministic impact of genes on the expression of behavior will contribute to the demystification of behavioral disorders.

Association study between dopamine D3 receptor gene variant and personality traits

Dopamine receptor gene variation has been hypothesized to influence personality traits characterized by novelty seeking and related traits. We analyzed a dopamine D(3) receptor gene (DRD3) variant in a Swedish population (n = 373) investigated with one or more of several personality questionnaires. No significant relationships were found between DRD3 genotypes and any of the 15 Karolinska Scales of Personality (KSP) and five Health-relevant Personality 5 factor inventory (HP5i) scales. The DRD3 variant was associated with some scales related to novelty seeking: the Swedish universities Scales of Personality (SSP) Adventure Seeking and the revised NEO personality inventory (NEO-PI-R) Fantasy (O1) and Order (C2) scales. There were also associations with the Temperament and Character Inventory (TCI) Cooperativeness and Compassion (C4) scales. After correction for multiple testing, however, no significant difference remained. We conclude that the investigated DRD3 polymorphism does not have a major impact on personality in the investigated population.

Dopamine D 4 receptor gene polymorphism and extraversion revisited: results from the Munich gene bank project for alcoholism

In 1998 a gene bank project for association studies in alcoholism was initiated at the Psychiatric Hospital of Munich. The research instruments used were partly adopted from the US collaborative study of the genetics of alcoholism and include the family history assessment module (FHAM), the semi-structured interview for assessment of genetics in alcoholism (SSAGA) and a number of personality inventories such as the Zuckerman's sensation-seeking scale, the NEO Five factor inventory and the temperament and character inventory. Based on the examination of 181 alcoholic subjects, no association was found between Dopamine D4 receptor gene polymorphism and novelty-seeking or extraversion as assessed by the three personality inventories. These findings are in line with a number of more recent studies questioning the association between novelty-seeking and DRD4 dopamine receptor gene polymorphism. Possible implications of these findings are discussed.

Ethnic heterogeneity in allele variation in the DRD4 gene in schizophrenia

The goal of the present study was to use a meta-analysis on previous studies plus our own unpublished data to confirm and extend findings which indicate that the variation in the dopamine D4 receptor (DRD4) gene is best represented by a mixture of two different ethnic groups. The genotype distribution was divided into either a long or short form using a mixture analysis of normal controls of different ethnic origins under the assumption that there is a single major gene. The meta-analysis was based on the data from 19 independent samples, 18 association studies, and from our own unpublished data, including a total of 1431 schizophrenic patients (sporadic cases 1309, familial cases 122) and 1439 controls. No significant genotype differences were noted between patients and controls for the whole sample. However, reorganization of the studies into different groups by the geographical origin of samples revealed significant ethnic heterogeneity. In addition, there was a significant association between the long form of DRD4 gene and schizophrenia in Caucasians, especially those with familial schizophrenia.

DRD4 and novelty seeking: results of meta-analyses

Studies of the association between polymorphisms within and near the dopamine D4 receptor (DRD4) gene and novelty seeking (NS) have produced inconsistent results, raising questions about the strength of the relationship and the methodological conditions under which the relationship holds. We conducted three meta-analyses of existing studies to provide formal statistical measures of the strength of the DRD4-NS relationship. Results provided no support for a relationship between NS and the presence of the 7-repeat allele of the VNTR polymorphism. A small positive effect, however, was found for long repeats of the same polymorphism. The most promising findings were obtained for the relationship with the -521 C/T promoter polymorphism, for which the analysis showed an effect size of 0.32. The positive findings are consistent with a polygenic model of influence on fundamental personality dimensions.