No association between dopamine D4 receptor gene variants and novelty seeking

Emotionality vs. Other Biobehavioural Traits: A Look at Neurochemical Biomarkers for Their Differentiation

This review highlights the differential contributions of multiple neurochemical systems to temperament traits related and those that are unrelated to emotionality, even though these systems have a significant overlap. The difference in neurochemical biomarkers of these traits is analysed from the perspective of the neurochemical model, Functional Ensemble of Temperament (FET) that uses multi-marker and constructivism principles. Special attention is given to a differential contribution of hypothalamic-pituitary hormones and opioid neuropeptides implicated in both emotional and non-emotional regulation. The review highlights the role of the mu-opioid receptor system in dispositional emotional valence and the role of the kappa-opioid system in dispositional perceptual and behavioural alertness. These opioid receptor (OR) systems, microbiota and cytokines are produced in three neuroanatomically distinct complexes in the brain and the body, which all together integrate dispositional emotionality. In contrast, hormones could be seen as neurochemical biomarkers of non-emotional aspects of behavioural regulation related to the construction of behaviour in fast-changing and current situations. As examples of the role of hormones, the review summarised their contribution to temperament traits of Sensation Seeking (SS) and Empathy (EMP), which FET considers as non-emotionality traits related to behavioural orientation. SS is presented here as based on (higher) testosterone (fluctuating), adrenaline and (low) cortisol systems, and EMP, as based on (higher) oxytocin, reciprocally coupled with vasopressin and (lower) testosterone. Due to the involvement of gonadal hormones, there are sex and age differences in these traits that could be explained by evolutionary theory. There are, therefore, specific neurochemical biomarkers differentiating (OR-based) dispositional emotionality and (hormones-based) body's regulation in fast-changing events. Here we propose to consider dispositional emotionality associated with OR systems as emotionality in a true sense, whereas to consider hormonal ensembles regulating SS and EMP as systems of behavioural orientation and not emotionality.

DRD4 Exon 3 Gene Polymorphisms in Patients Diagnosed with Polysubstance Use Disorder and Co-Occurrence of a Depressive Episode

Background: There has been a noticeable and systematic growth of the use of psychoactive substances over the past few decades. Dual diagnosis is a clinical term referring to the occurrence of psychoactive substance use disorder comorbid with another psychiatric disorder in the same person. The most common type of dual diagnosis is the co-occurrence of alcohol use disorder and mood disorders in the form of a depressive episode. Co-occurrent substance use disorders are frequently influenced by genetic factors. In selecting our area of research, we focused on dopamine and the DRD4 (Dopamine Receptor D4) gene polymorphism as well as associations with personality features. The aim of the study: The aim of the study was to compare DRD4 exon 3 (DRD4 Ex3) gene polymorphisms in patients diagnosed with polysubstance use disorder and co-occurrence of a depressive episode to DRD4 exon 3 gene polymorphisms in patients diagnosed with polysubstance use disorder and without co-occurrence of a depressive episode and a group of healthy volunteers. The study also aimed at establishing associations between personality features and DRD4 exon 3 gene polymorphisms of male patients diagnosed with polysubstance use disorder with co-occurrence of a depressive episode which may present a specific endophenotype of this group of patients. Methods: The study group comprised 602 male volunteers: patients diagnosed with polysubstance use disorder comorbid with a depressive episode (PUD MDD) (n = 95; mean age = 28.29, standard deviation (SD) = 7.40), patients diagnosed with polysubstance use disorder (PUD) (n = 206; mean age = 28.13, SD = 5.97), and controls (n = 301; mean age = 22.13, SD = 4.57). The patients and control subjects were diagnosed by a psychiatrist using the Mini International Neuropsychiatric Interview (MINI), the NEO Five-Factor Personality Inventory (NEO-FFI), and the State-Trait Anxiety Inventory (STAI) questionnaires. An analysis of the DRD4 exon 3 polymorphism was performed. Results: The patients diagnosed with PUD MDD compared to the control group of healthy volunteers showed significantly higher scores on both the STAI status and features scale and the NEO-FFI Neuroticism and Openness Scale, as well as lower scores on the Extraversion, Agreeableness, and Conscientiousness NEO-FFI scales. In the DRD4 exon 3 gene polymorphism, the s allele was more frequent in the PUD MDD compared to the l allele, which was less frequent. The results of the 2 × 3 factor analysis of variance (ANOVA) in patients and controls and the variant DRD4 exon 3 interaction were found on the Extraversion Scale and the Conscientiousness Scale of the NEO-FFI. Conclusions: The associations show that psychological factors combined with genetic data create a new area of research on addiction, including the problem of dual diagnosis. However, we want to be careful and draw no definite conclusions at this stage of our research.

Third generation antipsychotic drugs: partial agonism or receptor functional selectivity?

Functional selectivity is the term that describes drugs that cause markedly different signaling through a single receptor (e.g., full agonist at one pathway and antagonist at a second). It has been widely recognized recently that this phenomenon impacts the understanding of mechanism of action of some drugs, and has relevance to drug discovery. One of the clinical areas where this mechanism has particular importance is in the treatment of schizophrenia. Antipsychotic drugs have been grouped according to both pattern of clinical action and mechanism of action. The original antipsychotic drugs such as chlorpromazine and haloperidol have been called typical or first generation. They cause both antipsychotic actions and many side effects (extrapyramidal and endocrine) that are ascribed to their high affinity dopamine D(2) receptor antagonism. Drugs such as clozapine, olanzapine, risperidone and others were then developed that avoided the neurological side effects (atypical or second generation antipsychotics). These compounds are divided mechanistically into those that are high affinity D(2) and 5-HT(2A) antagonists, and those that also bind with modest affinity to D(2), 5-HT(2A), and many other neuroreceptors. There is one approved third generation drug, aripiprazole, whose actions have been ascribed alternately to either D(2) partial agonism or D(2) functional selectivity. Although partial agonism has been the more widely accepted mechanism, the available data are inconsistent with this mechanism. Conversely, the D(2) functional selectivity hypothesis can accommodate all current data for aripiprazole, and also impacts on discovery compounds that are not pure D(2) antagonists.

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.

The polymorphic nature of the human dopamine D4 receptor gene: a comparative analysis of known variants and a novel 27 bp deletion in the promoter region

BACKGROUND

The human dopamine D4 receptor (DRD4) is a candidate gene of great interest in molecular studies of human personality and psychiatric disorders. This gene is unique in having an exceptionally high amount of polymorphic sites both in the coding and in the promoter region.

RESULTS

We report the identification of a new 27 bp deletion starting 524 bp upstream of the initiation codon (27 bp del) of the dopamine D4 receptor (DRD4) gene, in the close vicinity of the -521C>T SNP. The presence of the 27 bp deletion leads to the misgenotyping of the -616C>G SNP by the Sau96 I RFLP method, thus the genotype determination of the mutation is of additional importance. The frequency of this novel sequence variation is considerably low (allele frequency is = 0.16%), as no homozygotes, and only 3 heterozygote carriers were found in a healthy, unrelated Caucasian sample (N = 955).

CONCLUSION

Remarkably, the deleted region contains consensus sequences of binding sites for several known transcription factors, suggesting that the different alleles may affect the transcriptional regulation of the gene. A comparison of methods and results for the allelic variations of the DRD4 gene in various ethnic groups is also discussed, which has a high impact in psychiatric genetic studies.

Attention-Deficit Hyperactivity Disorder in the post-genomic era

BACKGROUND

ADHD is a common and complex genetic disorder. Genetic risk factors are expected to be multiple, have small effect sizes when considered individually and to interact with each other and with environmental factors.

OBJECTIVE

To describe the difficulties involved in the genetic investigation of such a complex disorder and give a prospective for the future.

METHODS

Review based on empirical literature and project description.

RESULTS

Considerable progress has been achieved through the association analysis of candidate gene loci. Linkage scans using affected sibling pairs have identified a number of potential loci that may lead to the identification of novel genes of moderate effect size. Quantitative trait locus (QTL) approaches provide powerful complementary strategies that have the potential to link the categorical disorder to continuously distributed traits associated more closely with underlying genetic liability in the general population. Success in identifying some associated genes has been complemented by functional studies that seek to understand the mode of action of such genes.

CONCLUSION

Progress in understanding the mechanisms involved has not been straightforward and many inconsistencies have arisen. In order to take advantage of the potential for progress that stems from the genetic findings it will be important to draw upon a variety of approaches and experimental paradigms. A functional genomic approach to ADHD means that investigation of gene function is carried out at various levels of analysis, not only at the level of molecular and cellular function but also at the level of psychological processes, neuronal networks, environmental interactions and behavioural outcomes.

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.

A polymorphism of the beta1-adrenergic receptor is associated with low extraversion

BACKGROUND

We examined the possibility that allelic variation leading to alterations in beta(1)-adrenergic function might be present in persons with elevated social anxiety-related traits.

METHODS

A sample of 504 undergraduate college students were phenotyped on a personality inventory (the NEO-Personality Inventory-Revised) and measures of shyness and social anxiety and genotyped for two beta(1) adrenergic (ADRB1 gene) polymorphisms: a serine/glycine substitution at amino acid 49 (Ser49Gly) and an arginine/glycine substitution at residue 389 (Arg389Gly). We hypothesized that the Gly49 variant (thought to be functional), but not variation at Arg389Gly, would be associated with (low) extraversion and shyness. We evaluated the potential for population stratification artifact by genotyping a set of 36 unlinked, highly polymorphic markers previously demonstrated to sufficiently distinguish the ancestry of major American populations.

RESULTS

Presence of a Gly49 allele was associated with an increased odds of having low or very low extraversion (odds ratio = 1.68, 95% confidence interval 1.05-2.71). The Arg389Gly polymorphism, although in tight linkage disequilibrium (D' = -1.00) with Ser49Gly, was not significantly associated with level of extraversion. Formal testing showed that population structure did not explain the findings.

CONCLUSIONS

The Ser49Gly functional polymorphism in the beta(1) adrenergic receptor might explain some of the population variance in extraversion and related personality traits. Population structure was excluded as an explanation for these findings. We used a sufficient marker set to exclude possible population stratification artifact. These findings should be replicated and extended to the study of psychiatric disorders marked by low extraversion, namely social phobia and other phobic disorders.

Association of a duplicated repeat polymorphism in the 5'-untranslated region of the DRD4 gene with novelty seeking

Novelty Seeking (NS) is a human personality trait in which impulsive, exploratory, and thrill-seeking behaviors are displayed. Dopaminergic genes have been prime candidates in the search for the genetic factors underlying NS because of the central role that dopamine plays in the brain's reward system. We have investigated whether there is an association between a polymorphic 120 base pairs (bp) repeat that is located in the 5'-untranslated region of the dopamine D4 receptor gene (DRD4) and NS. We genotyped four separate groups from psychiatric clinical studies for the repeat polymorphism. There were significant associations with NS in the groups of bipolar (P = 0.01) and alcoholic (P = 0.006) families containing 267 and 172 subjects, respectively. Subjects who were homozygous for the single-copy allele (SS genotype) had higher mean NS scores. This trend was also observed in the two other studies that contained unrelated subjects diagnosed with depression (N = 143 and N = 148) but the associations between DRD4 duplication genotype and NS were not significant in these groups. In the data combined from all four clinical groups those genotyped as SS had higher mean scores for all four NS subscales with significant associations for impulsivity (P = 0.0006), extravagance (P = 0.04), disorderliness (P = 0.02), and total NS (P = 0.0003). However, given the low frequency of the single-copy allele, this polymorphism would account for only a small proportion of the variance of NS in the population.

Monoamine related functional gene variants and relationships to monoamine metabolite concentrations in CSF of healthy volunteers

BACKGROUND

Concentrations of monoamine metabolites in human cerebrospinal fluid (CSF) have been used extensively as indirect estimates of monoamine turnover in the brain. CSF monoamine metabolite concentrations are partly determined by genetic influences.

METHODS

We investigated possible relationships between DNA polymorphisms in the serotonin 2C receptor (HTR2C), the serotonin 3A receptor (HTR3A), the dopamine D4 receptor (DRD4), and the dopamine beta-hydroxylase (DBH) genes and CSF concentrations of 5-hydroxyindolacetic acid (5-HIAA), homovanillic acid (HVA), and 3-methoxy-4-hydroxyphenylglycol (MHPG) in healthy volunteers (n = 90).

RESULTS

The HTR3A 178 C/T variant was associated with 5-HIAA levels (p = 0.02). The DBH-1021 heterozygote genotype was associated with 5-HIAA (p = 0.0005) and HVA (p = 0.009) concentrations. Neither the HTR2C Cys23Ser variant, nor the DRD4 -521 C/T variant were significantly associated with any of the monoamine metabolites.

CONCLUSIONS

The present results suggest that the HTR3A and DBH genes may participate in the regulation of dopamine and serotonin turnover rates in the central nervous system.

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.

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 a promoter dopamine D2 receptor gene variant and the personality trait detachment

BACKGROUND

Personality traits have shown considerable heritable components. Striatal dopamine D(2) receptor density, as determined by positron-emission tomography, has been associated with detached personality, as assessed by the Karolinska Scales of Personality. A putative functional promoter polymorphism in the dopamine D(2) receptor gene (DRD2), -141C ins/del, has been associated with dopamine D(2) receptor density.

METHODS

In this study healthy subjects (n = 235) who filled in at least one of several personality questionnaires (Karolinska Scales of Personality, Swedish Universities Scales of Personality, Health-relevant Five-factor Personality Inventory, and Temperament and Character Inventory) were analyzed with regard to the DRD2 -141C ins/del variant.

RESULTS

There was an association (p =.001) between the DRD2 -141C ins/del variant and Karolinska Scales of Personality Detachment scale, indicating higher scores in subjects with the -141C del variant. There were also associations between the DRD2 -141C ins/del variant and a number of Karolinska Scales of Personality and Swedish Universities Scales of Personality Neuroticism-related scales, but of these only Swedish Universities Scales of Personality Lack of Assertiveness scale (p =.001) survived correction for multiple testing.

CONCLUSIONS

These results add further support for the involvement of dopamine D(2) receptor in certain personality traits. The results should be treated with caution until replicated.

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.

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.