No association of the -521 C/T polymorphism in the promoter of DRD4 with 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.

Genetic and gene-environment interaction effects on preschoolers' social behaviors

This study examined effects from a specific dopamine receptor gene (DRD4), environmental influences from parents and peers, and the interaction between them, on aggressive and prosocial behaviors of preschoolers. Children were classified as DRD4-L (n = 27) if they had at least one DRD4 allele with six to eight repeats and as DRD4-S (n = 35) if not. Parent-child interactions were coded when children were 3-4 years old. Peer interaction data and parent questionnaires were collected at age 5. DRD4-L children shared less with each other and parents were less sensitive during parent-twin triadic interactions. Also, genotype interacted with peer aggression to affect children's aggression during a peer play interaction at age 5, and genotype interacted with prior parental sensitivity to affect later externalizing problems. Thus, children having a certain genetic disposition may be more sensitive to certain environmental stimuli and therefore more likely to exhibit aggressive behaviors under more stressful circumstances.

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.

Genetic structure of the dopamine receptor D4 gene (DRD4) and lack of association with schizophrenia in Japanese patients

In order to investigate the contribution of genetic variation in the human dopamine receptor D4 gene (DRD4) to the risk of developing schizophrenia, we carried out a genetic analysis of 27 polymorphisms in 216 schizophrenic patients and 243 healthy controls from the Kyushu region of Japan. Twenty-two single nucleotide polymorphisms (SNPs) and five insertion/deletion polymorphisms were analyzed in this study, including four novel SNPs and a novel mononucleotide repeat. Linkage disequilibrium (LD) and haplotype analyses reveal weak LD across the DRD4 gene. In univariate analysis female individuals with allele -521C had a higher risk for schizophrenia. However, this finding was not significant after correction for multiple hypothesis testing. No other polymorphisms or haplotypes differed between schizophrenic patients and controls. Likewise, multivariate analyses did not reveal any statistically significant associations.

Relationship between dopamine system genes and extraversion and novelty seeking

Dopamine transmission is known to play an important role in the reinforcement system of the brain. Studies have identified dopamine system genes whose polymorphic variants have been linked with the intensity of psychological traits reflecting the tendency to form behaviors characterized by impulsivity and the need for additional stimulation. The aim of the present work was to seek associations between polymorphisms in the catechol-O-methyltransferase (COMT) and D4 dopamine receptor (DRD4) genes and personality traits in the Russian population. Studies of 130 subjects showed that carriers of the Met/Met genotype of the COMT gene had a greater intensity of the novelty-seeking trait than carriers of the Val/Val and Val/Met genotypes, though this association was seen only in women. In addition, the presence of the C allele of the DRD4 gene in carriers of the Met/Met genotype showed high levels of extraversion and hypomania. These results are consistent with current theoretical concepts of the regulation of dopamine transmission in the brain.

Smoking cessation, weight gain, and DRD4 -521 genotype

We investigated change in body mass index following long-term smoking cessation in a representative cohort of treatment-seeking heavy smokers in the United Kingdom, to determine the extent of long-term weight gain in successful quitters versus continuing smokers. We further investigated whether DRD4 genotype moderated any weight gain in either group. Smoking cessation was associated with an increase in BMI, and persisted up to 8 years after smoking cessation. Ex-smokers at 8-year follow-up weighed over 2.5 kg/m(3) more on average than they did at baseline, while participants who were smokers at both baseline and 8-year follow-up did not demonstrate any change in BMI. We did not observe an interaction between smoking status and DRD4 genotype. However, independently of the weight gain among those who stopped smoking during the course of the study, DRD4 genotype was significantly associated with BMI, with possession of the -521 C-allele associated with increased BMI. The magnitude of increase in BMI following smoking cessation, and the persistence of this change at 8-year follow-up, suggests that health benefits associated with smoking cessation may to some extent be negated by the detrimental effects on health of associated weight gain. Smoking cessation programmes should therefore consider incorporating follow-up support to promote weight loss among those who successfully stop smoking.

No direct effect of the -521 C/T polymorphism in the human dopamine D4 receptor gene promoter on transcriptional activity

Background

The human dopamine D4 receptor (DRD4) gene has been studied extensively as a candidate gene for certain psychological traits and several behavioural and psychiatric disorders. Both the 5' regulatory region and the coding sequence contain a number of polymorphisms. The promoter variants have received particular attention in the past few years due to their possible role in the regulation of gene transcription. Previously, the -521C/T SNP was shown to influence promoter activity. The aim of this study is to perform an in-depth analysis of this effect in the context of various neural cell lines.

Results

Endogenous mRNA expression of the DRD4 gene was demonstrated in two neuroblastoma (SK-N-F1, IMR32) and one retinoblastoma cell line (Y79) by RT-PCR. In addition, very low DRD4 mRNA levels were also detected in HeLa cells. The transcriptional activity of a series of 5' promoter deletion mutants was determined by transient transfection of luciferase reporter constructs. The activity profile of these promoter fragments was similar in each of the cell lines tested. The highest luciferase reporter activity was obtained with a construct containing promoter sequences between nucleotides -668 to -389, while a putative silencer region was localised spanning from nucleotide -1571 to -800. Surprisingly, the -521 C/T polymorphism had no significant effect on transcriptional activity of the reporter construct with the highest activity (-668 to -389) in any of the three cell lines tested.

Conclusion

Our results do not confirm previous data assigning different transcriptional activities to the -521 C/T alleles of the human DRD4 promoter. Furthermore, these findings highlight the need for further characterization of the 5' regulatory region of the DRD4 gene and identification of additional functional promoter polymorphic sites, especially in the context of haplotype.

Ethological resolution of behavioral topography and D2-like vs. D1-like agonist responses in congenic D4 dopamine receptor "knockouts": identification of D4:D1-like interactions

To clarify the involvement of dopamine D4 receptors in behavioral regulation, the phenotypic ethogram of congenic D4 "knockout" mice was studied in terms of (i) course of exploration and habituation, and (ii) topographical responsiveness to the selective D2-like agonist RU 24213 and the selective D1-like agonists A 68930, SK&F 83959 and SK&F 83822. Congenic D4 knockouts were characterized by a small reduction in exploratory sniffing with delayed habituation of sifting. The magnitude and topographical specificity of these effects indicated that any functional role for D4 receptors in exploratory processes is subtle. Induction of stereotyped, ponderous locomotion by RU 24213 was reduced in D4-null mice consistent with an involvement of D4 receptors in the topographical expression of stereotypy. Induction of grooming and, at higher doses, seizures by A 68930, which stimulates both adenylyl cyclase (AC) and phospholipase C (PLC), were unaltered in congenic D4 knockouts. In contrast, induction of grooming by SK&F 83959, which stimulates PLC but not AC and fails to induce seizures, was reduced in D4-null mice; this indicates that D4 receptors interact with PLC-coupled D1-like receptors in regulating D1-like-mediated grooming. Conversely, induction of seizures by SK&F 83822, which stimulates AC but not PLC and fails to induce grooming, was reduced in congenic D4 knockouts; this indicates that D4 receptors interact with AC-coupled D1-like receptors in regulating D1-like-mediated seizures. These studies identify novel functional roles for the D4 receptor that are distinct from those of closely related D2-like family members and involve interactions with their D1-like counterparts.

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.

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.

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 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.

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.

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.

DRD4 promoter SNPs and gender effects on Extraversion in African Americans

There is strong evidence for genetic influences on personality traits. Interest in one such gene, the dopamine D4 receptor (DRD4) grew after an exon III polymorphism was associated with Novelty Seeking and related measures of Extraversion. However, the findings were not confirmed in later studies. Recently, a -521C/T single nucleotide polymorphism (SNP) within the promoter region of the DRD4 gene was found to be related to Novelty Seeking scores in populations from Japan and Hungary. Since little is known about the role DRD4 plays in personality in other populations we evaluated if two DRD4 promoter SNPs, -521C/T and -616C/G, were related to personality traits in African Americans. Personality traits were measured by the NEO-FFI in 71 unrelated African Americans. Genotyping was performed using PCR-RFLP. Multivariate analyses of variance (MANOVA) were performed to evaluate the effects of gender and -616 and -521 genotypes on personality traits. A significant three-way interaction effect from gender, -616 genotype, and -521 genotype was observed for Extraversion scores (F(1,54) 5.86, P < 0.02). Subsequent analyses revealed that the association was mainly due to -521C/T genotype among females (P = 0.01). This study provides further evidence that genetic variation within the DRD4 promoter and gender differences contribute to variation in Novelty Seeking behaviors such as Extraversion.