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

Anxious-depressive attack and rejection sensitivity-Toward a new approach to treatment-resistant depression

This paper aimed to find clues to treatment-resistant depression (TRD) solutions. Depression comorbid with anxiety is often treatment-resistant where anxious-depressive attack (ADA) often lurks. ADA is a recently proposed clinical idea for just a psychological version of a panic attack. It mostly begins with an abrupt surge of intense anxiety followed by uninterrupted intrusive thoughts; lasting ruminations about regret or worry produced by violent anxiety, agitation, and loneliness. Acting-out behaviors such as deliberate self-injury and over-dose may also be observed during the attack. As the basic psychopathology of ADA, rejection sensitivity (RS) was revealed by a structural equation model. It is said that the presence of RS in depressive disorders implies a poor prognosis. The following biological markers for RS were reviewed in the literature: first, the involvement of the μ-opioid receptor function in RS and, secondly, hypersensitivity of the dopamine D4 receptor (DRD4) in the medial prefrontal cortex. The latter has been suggested in fear-conditioned animal experiments. Manipulation of the μ-opioid receptor function together with the DRD4 function may culminate in a treatment for RS, which could contribute to the development of a treatment for TRD via the improvement of ADA.

Quo Vadis Psychiatry? Why It Is Time to Endorse Evolutionary Theory

In recent decades, psychiatry and the neurosciences have made little progress in terms of preventing, diagnosing, classifying, or treating mental disorders. Here we argue that the dilemma of psychiatry and the neurosciences is, in part, based on fundamental misconceptions about the human mind, including misdirected nature-nurture debates, the lack of definitional concepts of "normalcy," distinguishing defense from defect, disregarding life history theory, evolutionarily uninformed genetic and epigenetic research, the "disconnection" of the brain from the rest of the body, and lack of attention to actual behavior in real-world interactions. All these conceptual difficulties could potentially benefit from an approach that uses evolutionary theory to improve the understanding of causal mechanisms, gene-environment interaction, individual differences in behavioral ecology, interaction between the gut (and other organs) and the brain, as well as cross-cultural and across-species comparison. To foster this development would require reform of the curricula of medical schools.

Chronic pain and delinquency partially explain the effect of the DRD4 gene polymorphism on adult substance use

Background: The dopamine receptor D4 [DRD4] has been reported to be associated with substance use. Yet, the roles that health conditions and behaviors may play in such association are understudied.Objective: This longitudinal study investigated the potential mediation effects of chronic pain and delinquency in adolescence on the association between the DRD4 2-repeat allele and substance use in adulthood. Sex, witnessing violence, and experiencing violence were also examined as potential moderators for the mediation pathways.Methods: We used the restricted and candidate gene data from the National Longitudinal Study of Adolescent to Adult Health (Waves I-IV) to conduct secondary analysis (N = 8,671; 47% male). A two-step approach was adopted to examine the mediation effects regarding four substance use outcomes in adulthood: number of lifetime alcohol use disorder symptoms, lifetime regular smoker status, past-month smoking, and lifetime "pain killer" misuse. The moderation effects were investigated using stratification and permutation.Results: The DRD4 2-repeat allele was associated with all adulthood substance use outcomes through adolescent chronic pain and delinquency (AORs/IRR range 1.08-3.78; all ps<0.01). The association between delinquency and smoking was higher among females. The association between delinquency and substance use was lower among the participants who witnessed violence in adolescence.Conclusions: This study identified modifiable mediators underlying the association between the DRD4 2-repeat allele and substance use behaviors, concluding that chronic pain and delinquency partially explain the effect of the DRD4 gene polymorphism on adult substance use.

Association of Neurotensin Receptor 1 Gene Polymorphisms With Defense Mechanisms in Healthy Chinese

Aims: In the central nerve system, neurotensin (NT), and neurotensin receptor 1 (NTR1) modulate the dopamine system. Gene variations in the dopamine system have been demonstrated to influence certain defense mechanisms, but no studies have investigated possible effect of NTR1 gene polymorphisms in the biological determination of these defenses. The present study therefore examined this link. Methods: In 412 healthy Han Chinese, single nucleotide polymorphisms rs6090453C/G, rs6011914C/G, and rs2427422A/G of the NTR1 gene were genotyped, and the defense mechanisms were measured by the self-reporting Defense Style Questionnaire 88. Results: Significant male-specific differences in the projective identification among the rs6090453 genotypes (p = 0.003); in the intermediate defense, reaction formation, and projective identification among the rs6011914 genotypes (p = 0.011, 0.010, and 0.011, respectively); and in the projective identification among the rs2427422 genotypes (p = 0.005) were found when the level of significance was adjusted by the Bonferroni correction. There was no significant difference in any of the defense scores among genotypes of any single nucleotide polymorphism in the total cohort or female subjects (all p > 0.017). The distributions of genotypes between the low and high score subgroups showed significant differences in the rs2427422 genotype distributions for help-rejecting complaining, regression, and projective identification (p = 0.010, 0.022, and 0.044, respectively). Significant differences were found between males and females in 10 defense mechanisms (all P < 0.05). Conclusions: The gene variations in the NTR1 polymorphisms were involved in the biological mechanisms of intermediate defense mechanisms, and this effect was influenced by sex.

Associations Among Internet Addiction, Genetic Polymorphisms, Family Functioning, and Psychopathological Risk: Cross-Sectional Exploratory Study

BACKGROUND

International research has emphasized that youths are at higher risk for the onset of internet addiction (IA), but studies investigating biological, psychological, and social factors associated with this condition are limited.

OBJECTIVE

This study aims to investigate the possible association between IA and genetic polymorphisms in monoamine oxidase A (MAO-A), serotonin-transporter (5-HTTPR), dopamine receptor (DRD4), and dopamine transporter (DAT1) genes by considering the role played by the perception of young adults in their family functioning and their depression, anxiety, and avoidant personality problems.

METHODS

In a sample of 104 male and female young adults aged between 19 and 23 years (mean age 21.87, SD 2.29 years) recruited from universities in the central southern part of Italy, we addressed the presence of IA using the Young criteria of the IA test. Moreover, the perception of young adults of their family functioning and their psychopathological symptoms were assessed through the Family Assessment Device (FAD) and the Adult Self-Report, respectively.

RESULTS

We found no significant association between IA and any genetic polymorphisms, neither among males or females. Young adults with IA reported significantly higher scores in the subscale of FAD affective responsiveness (AR; P=.01) and in depressive problems (P=.02), anxiety problems (P=.009), and avoidant personality problems (P=.003) than those in the control group. Results of mediation analyses showed a mediation role played by depressive symptoms (B=0.99; 95% CI 0.22 to 1.97) and avoidant personality problems (B=1.09; 95% CI 0.32 to 2.05) of young adults on the relationship between the FAD, AR, and IA. Finally, this relationship was moderated by the genotype of the 5-HTTLPR (P<.001), DAT1 (P<.001), and MAO-A (P<.001) genes in young adults.

CONCLUSIONS

This exploratory study supports the recent evidence on the mutual relationship among biological, individual, and social risk factors associated with IA in young adulthood. Our findings may have important clinical implications for the development of prevention and treatment programs.

The Dopamine D4 Receptor (DRD4) Exon 3 VNTR Contributes to Adaptive Personality Differences in an Italian Small Island Population

The search for evolutionary forces shaping the diversity of human personality traits encouraged studies that have found that islanders are relatively closed and introverted, with little interest in the external world. The ‘personality gene flow’ hypothesis was proposed to explain the mechanism underlying this difference, suggesting that the frequency of alleles that influence islander personality traits might progressively increase in the gene pools on islands because of selective emigration of individuals not displaying these alleles. We genotyped 96 individuals from the Italian mainland and 117 from Giglio Island, whose residents were previously assessed regarding their personality traits. We genotyped three polymorphisms: the dopamine D4 receptor (DRD4) exon 3 repeat region, the serotonin–transporter SLC6A4 5–HTTLPR indel and the dopamine transporter SLC6A3 DAT1 3′UTR repeat region. Only the DRD4 exon 3 repeat was hypothesised to show varying allele frequencies because this polymorphism could be associated with human migration and personality traits such as extraversion, openness and novelty seeking. As predicted, no differences in allele frequencies were found for the SLC6A4 and SLC6A3 polymorphisms, whereas significant differences were observed in the frequency of the DRD4 exon 3 alleles. The DRD4.2 repeat was more common in mainlanders, as expected, whereas the DRD4.7 allele was over–represented among islanders who never emigrated. This last result contradicts the suggested association of this allele with long–distance migrations. We suggest that emigration might have caused gene flow out the island that resulted in somewhat unpredictable changes in the frequencies of specific alleles, thus influencing islander personality traits. Copyright © 2013 European Association of Personality Psychology

DRD4 polymorphisms modulate reward positivity and P3a in a gambling task: Exploring a genetic basis for cultural learning

Prior work shows that people respond more plastically to environmental influences, including cultural influences, if they carry the 7 or 2-repeat (7/2R) allelic variant of the dopamine D4 receptor gene (DRD4). The 7/2R carriers are thus more likely to endorse the norms and values of their culture. So far, however, mechanisms underlying this moderation of cultural acquisition by DRD4 are unclear. To address this gap in knowledge, we tested the hypothesis that DRD4 modulates the processing of reward cues existing in the environment. About 72 young adults, preselected for their DRD4 status, performed a gambling task, while the electroencephalogram was recorded. Principal components of event-related potentials aligned to the Reward-Positivity (associated with bottom-up processing of reward prediction errors) and frontal-P3 (associated with top-down attention) were both significantly more positive following gains than following losses. As predicted, the gain-loss differences were significantly larger for 7/2R carriers than for noncarriers. Also, as predicted, the cultural backgrounds of the participants (East Asian vs. European American) did not moderate the effects of DRD4. Our findings suggest that the 7/2R variant of DRD4 enhances (a) the detection of reward prediction errors and (b) controlled attention that updates the context for the reward, thereby suggesting one possible mechanism underlying the DRD4 × Culture interactions.

Cultural variation in the gray matter volume of the prefrontal cortex is moderated by the dopamine D4 receptor gene (DRD4)

Recent evidence suggests a systematic cultural difference in the volume/thickness of prefrontal regions of the brain. However, origins of this difference remain unclear. Here, we addressed this gap by adopting a unique genetic approach. People who carry the 7- or 2-repeat (7/2-R) allele of the dopamine D4 receptor gene (DRD4) are more sensitive to environmental influences, including cultural influences. Therefore, if the difference in brain structure is due to cultural influences, it should be moderated by DRD4. We recruited 132 young adults (both European Americans and Asian-born East Asians). Voxel-based morphometry showed that gray matter (GM) volume of the medial prefrontal cortex and the orbitofrontal cortex was significantly greater among European Americans than among East Asians. Moreover, the difference in GM volume was significantly more pronounced among carriers of the 7/2-R allele of DRD4 than among non-carriers. This pattern was robust in an alternative measure assessing cortical thickness. A further exploratory analysis showed that among East Asian carriers, the number of years spent in the U.S. predicted increased GM volume in the orbitofrontal cortex. The present evidence is consistent with a view that culture shapes the brain by mobilizing epigenetic pathways that are gradually established through socialization and enculturation.

Associations Between the Dopamine D4 Receptor and DAT1 Dopamine Transporter Genes Polymorphisms and Personality Traits in Addicted Patients

Many factors are involved in addiction. The dopaminergic system is thought to be the key element in this process. The mesolimbic dopamine system is a crucial element in the reward system. Changes in this system are thought to be leading to substance use disorders and dependence. Therefore, for our study we chose an analysis of two polymorphisms in genes (Variable Number of Tandem Repeats in DRD4 and DAT1) responsible for dopaminergic transmission, which might be implicated in the scores of personality traits measured by the NEO-FFI test. The study group consisted of 600 male volunteers—299 addicted subjects and 301 controls. Both groups were recruited by psychiatrists; in the case group addiction was diagnosed; in the controls a mental illness was excluded. In both groups the same psychometric test and genotyping by the PCR VNTR method were performed. The results were investigated by a multivariate analysis of the main effects ANOVA. In the presented study no DRD4 main effects were found for any of the analyzed traits but the DRD4 main effects approximated to the statistical significance for the extraversion scale. However, no DAT1 main effects were found for any of the analyzed traits but the DAT1 main effects approximated to the statistical significance for the agreeability scale.These associations open new possibilities for addiction research.

Effects of the 2-Repeat Allele of the DRD4 Gene on Neural Networks Associated With the Prefrontal Cortex in Children With ADHD

Objective: Genetic variation, especially polymorphism of the dopamine D4 receptor gene (DRD4), has been linked to deficits in self-regulation and executive functions and to attention deficit hyperactivity disorder (ADHD), and is related to the structural and functional integrity of the default mode network (DMN), the executive control network (ECN) and the sensorimotor network (SMN). The aim of this study was to explore the effects of the 2-repeat allele of the DRD4 gene on brain network connectivity and behaviors in children with ADHD.

Methods: Using independent component analysis (ICA) and dimension analyses, we examined resting-state functional magnetic resonance imaging (fMRI) data obtained from 52 Asian medicine-naive children with ADHD (33 2-repeat absent and 19 2-repeat present).

Results: We found that individuals with 2-repeat absent demonstrated increased within-network connectivity in the right precuneus of the DMN, the right middle frontal gyrus (MFG) of the SMN compared with individuals with 2-repeat present. Within the ECN, 2-repeat absent showed decreased within-network connectivity in the left inferior frontal gyrus (IFG) and the left anterior cingulate cortex. A deeper study found that connectivity strength of the left IFG was directly proportional to the Stroop reaction time in 2-repeat absent group, and as well as the right MFG in 2-repeat present group.

Conclusion: Polymorphisms of the DRD4 gene, specifically 2-repeat allele, had effects on the ECN, the SMN and the DMN, especially in the prefrontal cortex (PFC) circles. ADHD children with DRD4 2-repeat allele have aberrant resting-state within-network connectivity patterns in the left IFG and the right MFG related to dysfunction in inattention symptom. This study provided novel insights into the neural mechanisms underlying the effects of DRD4 2-repeat allele on ADHD.

Dopamine D4 Receptor Gene Associated with the Frontal-Striatal-Cerebellar Loop in Children with ADHD: A Resting-State fMRI Study

Attention deficit hyperactivity disorder (ADHD) is a common childhood neuropsychiatric disorder that has been linked to the dopaminergic system. This study aimed to investigate the effects of regulation of the dopamine D4 receptor (DRD4) on functional brain activity during the resting state in ADHD children using the methods of regional homogeneity (ReHo) and functional connectivity (FC). Resting-state functional magnetic resonance imaging data were analyzed in 49 children with ADHD. All participants were classified as either carriers of the DRD4 4-repeat/4-repeat (4R/4R) allele (n = 30) or the DRD4 2-repeat (2R) allele (n = 19). The results showed that participants with the DRD4 2R allele had decreased ReHo bilaterally in the posterior lobes of the cerebellum, while ReHo was increased in the left angular gyrus. Compared with participants carrying the DRD4 4R/4R allele, those with the DRD4 2R allele showed decreased FC to the left angular gyrus in the left striatum, right inferior frontal gyrus, and bilateral lobes of the cerebellum. The increased FC regions included the left superior frontal gyrus, medial frontal gyrus, and rectus gyrus. These data suggest that the DRD4 polymorphisms are associated with localized brain activity and specific functional connections, including abnormality in the frontal-striatal-cerebellar loop. Our study not only enhances the understanding of the correlation between the cerebellar lobes and ADHD, but also provides an imaging basis for explaining the neural mechanisms underlying ADHD in children.

Dopamine genes are linked to Extraversion and Neuroticism personality traits, but only in demanding climates

Cross-national differences in personality have long been recognized in the behavioural sciences. However, the origins of such differences are debated. Building on reinforcement sensitivity theories and gene-by-environment interactions, we predict that personality trait phenotypes linked to dopaminergic brain functions (centrally involved in reward processing) diverge most strongly in climatically stressful environments, due to shifts in perceived rewards vs risks. Individuals from populations with a highly efficient dopamine system are biased towards behavioural approach traits (Extraversion and Emotional Stability) due to higher perceived reward values, whereas individuals from populations with a less efficient dopaminergic system are biased towards risk avoidance. In temperate climates, we predict smaller phenotypic differences due to overall weakened reward and risk ratios. We calculated a population-level index of dopamine functioning using 9 commonly investigated genetic polymorphisms encoding dopamine transporters and receptors, derived from a meta-analysis with data from 805 independent samples involving 127,685 participants across 73 societies or territories. We found strong support for the dopamine gene by climatic stress interaction: Population genetic differences in dopamine predicted personality traits at the population level in demanding climates, but not in temperate, less demanding climates, even when controlling for known correlates of personality including wealth and parasite stress.

Family-based association study of DRD4 gene in methylphenidate-responded Attention Deficit/Hyperactivity Disorder

The 48-basepair (48-bp) variable number tandem repeat (VNTR) polymorphism in exon 3 of the dopamine receptor D4 gene (DRD4) is implicated in the etiology of attention-deficit/ hyperactivity disorder (ADHD). In particular, ADHD in European-ancestry population is associated with an increased prevalence of the 7-repeat (7R) allele of the exon 3 VNTR. However, it is intriguing to note that the 7R allele has been found to be of very low prevalence in the Chinese general population. In a previous case-control study, our research team had found that the 7R allele was similarly absent in Chinese ADHD children in Hong Kong. Instead, there was an increased prevalence of the 2R allele in Chinese ADHD children. Interestingly, in Asian samples, the 2R allele had been found to be an evolutionary derivative of the 7R allele with equivalent biochemical functionality. So, the finding of an association between ADHD and 2R allele in Chinese population does not exactly contradict the original 7R allele finding in European-ancestry population. However, given the potential pitfall of population stratification in the previous case-control design, this current study tested the 2R allele and ADHD association using a methodologically more rigorous family-based approach on 33 Chinese ADHD probands who had favorable clinical responses to stimulant medication (methylphenidate). Haplotype Relative Risk (HRR) analysis and Transmission Disequilibrium Test (TDT) both showed a significant preferential transmission of the 2R allele from the biological parents to ADHD probands (p_one-tailed = 0.038, OR = 2.04; p_one-tailed = 0.048, OR = 2.29, respectively). A second hypothesis speculates that it is the deviation, including 7R and 2R alleles, from the conserved ancestral 4R allele which confers risk to ADHD. Thus, a preferential transmission of non-4R alleles, against the 4R allele, from biological parents to their ADHD probands is predicted. Both HRR analysis and TDT confirmed such prediction (p_one-tailed = 0.029, OR = 2.07; p_one-tailed = 0.032, OR = 2.43, respectively). This study re-confirmed the original finding of a previous study that in Chinese population, the 2R allele of the DRD4 exon 3 VNTR was related to ADHD. This endorses the general thesis that DRD4 exon 3 VNTR polymorphism is related to ADHD, despite that the exact length or number of repeats of the associated alleles varies across ethnicity. This in turn supports the dopamine dysregulation theory of ADHD.

Evidence of genotypic adaptation to the exposure to volcanic risk at the dopamine receptor DRD4 locus

Humans have colonized and adapted to extremely diverse environments, and the genetic basis of some such adaptations, for example to high altitude, is understood. In some cases, local or regional variation in selection pressure could also cause behavioural adaptations. Numerous genes influence behaviour, such as alleles at the dopamine receptor locus D4 (DRD4), which are associated with attitude toward risk in experimental settings. We demonstrate genetic differentiation for this gene, but not for five unlinked microsatellite loci, between high- and low risk environments around Mount Merapi, an active volcano in Java, Indonesia. Using a behavioural experiment, we further show that people inhabiting the high risk environment are significantly more risk averse. We provide evidence of a genetic basis for this difference, showing that heterozygotes at the DRD4 locus are more risk averse than either homozygotes. In the high risk environment, allele frequencies are equilibrated, generating a high frequency of heterozygotes. Thus it appears that overdominance (i.e. selective advantage of heterozygotes) generates negative frequency dependent selection, favouring the rarer allele at this locus. Our results therefore provide evidence for adaptation to a marginal habitat through the selection of a neurocognitive trait with a genetic basis.

Nature, Nurture, and Their Interplay

Cultural neuroscience research examines how psychological processes are affected by the interplay between culture and biological factors, including genetic influences, patterns of neural activation, and physiological processes. In this review, we present foundational and current empirical research in this area, and we also discuss theories that aim to explain how various aspects of the social environment are interpreted as meaningful in different cultures and interact with a cascade of biological processes to ultimately influence thoughts and behaviors. This review highlights theoretical and methodological issues, potential solutions, and future implications for a field that aspires to integrate the complexities of human biology with the richness of culture.

Religion priming and an oxytocin receptor gene (OXTR) polymorphism interact to affect self-control in a social context

Using a genetic moderation approach, this study examines how an experimental prime of religion impacts self-control in a social context, and whether this effect differs depending on the genotype of an oxytocin receptor gene (OXTR) polymorphism (rs53576). People with different genotypes of OXTR seem to have different genetic orientations toward sociality, which may have consequences for the way they respond to religious cues in the environment. In order to determine whether the influence of religion priming on self-control is socially motivated, we examine whether this effect is stronger for people who have OXTR genotypes that should be linked to greater rather than less social sensitivity (i.e., GG vs. AA/AG genotypes). The results showed that experimentally priming religion increased self-control behaviors for people with GG genotypes more so than people with AA/AG genotypes. Furthermore, this Gene × Religion interaction emerged in a social context, when people were interacting face to face with another person. This research integrates genetic moderation and social psychological approaches to address a novel question about religion's influence on self-control behavior, which has implications for coping with distress and psychopathology. These findings also highlight the importance of the social context for understanding genetic moderation of psychological effects.

Association between the dopamine D4 receptor gene exon III variable number of tandem repeats and political attitudes in female Han Chinese

Twin and family studies suggest that political attitudes are partially determined by an individual's genotype. The dopamine D4 receptor gene (DRD4) exon III repeat region that has been extensively studied in connection with human behaviour, is a plausible candidate to contribute to individual differences in political attitudes. A first United States study provisionally identified this gene with political attitude along a liberal-conservative axis albeit contingent upon number of friends. In a large sample of 1771 Han Chinese university students in Singapore, we observed a significant main effect of association between the DRD4 exon III variable number of tandem repeats and political attitude. Subjects with two copies of the 4-repeat allele (4R/4R) were significantly more conservative. Our results provided evidence for a role of the DRD4 gene variants in contributing to individual differences in political attitude particularly in females and more generally suggested that associations between individual genes, and neurochemical pathways, contributing to traits relevant to the social sciences can be provisionally identified.

Neurogenetic and Neuroimaging Evidence for a Conceptual Model of Dopaminergic Contributions to Obesity

As the incidence of obesity continues to rise, clinicians and researchers alike are seeking explanations for why some people become obese while others do not. While caloric intake and physical activity most certainly play a role, some individuals continue to gain weight despite careful attention to these factors. Increasing evidence suggests that genetics may play a role, with one potential explanation being genetic variability in genes within the neurotransmitter dopamine pathway. This variability can lead to a disordered experience with the rewarding properties of food. This review of literature examines the extant knowledge about the relationship between obesity and the dopaminergic reward pathways in the brain, with particularly strong evidence provided from neuroimaging and neurogenetic data. Pubmed, Google Scholar, and Cumulative Index to Nursing and Allied Health Literature searches were conducted with the search terms dopamine, obesity, weight gain, food addiction, brain regions relevant to the mesocortical and mesolimbic (reward) pathways, and relevant dopaminergic genes and receptors. These terms returned over 200 articles. Other than a few sentinel articles, articles were published between 1993 and 2013. These data suggest a conceptual model for obesity that emphasizes dopaminergic genetic contributions as well as more traditional risk factors for obesity, such as demographics (age, race, and gender), physical activity, diet, and medications. A greater understanding of variables contributing to weight gain and obesity is imperative for effective clinical treatment.

Specific and common genes implicated across major mental disorders: a review of meta-analysis studies

Major efforts have been directed at family-based association and case-control studies to identify the involvement of candidate genes in the major disorders of mental health. What remains unknown is whether candidate genes are associated with multiple disorders via pleiotropic mechanisms, and/or if other genes are specific to susceptibility for individual disorders. Here we undertook a review of genes that have been identified in prior meta-analyses examining specific genes and specific mental disorders that have core disruptions to emotional and cognitive function and contribute most to burden of illness- major depressive disorder (MDD), anxiety disorders (AD, including panic disorder and obsessive compulsive disorder), schizophrenia (SZ) and bipolar disorder (BD) and attention deficit hyperactivity disorder (ADHD). A literature review was conducted up to end-March 2013 which included a total of 1519 meta-analyses across 157 studies reporting multiple genes implicated in one or more of the five disorders studied. A total of 134 genes (206 variants) were identified as significantly associated risk variants for MDD, AD, ADHD, SZ or BD. Null genetic effects were also reported for 195 genes (426 variants). 13 genetic variants were shared in common between two or more disorders (APOE e4, ACE Ins/Del, BDNF Val66Met, COMT Val158Met, DAOA G72/G30 rs3918342, DAT1 40-bp, DRD4 48-bp, SLC6A4 5-HTTLPR, HTR1A C1019G, MTHR C677T, MTHR A1298C, SLC6A4 VNTR and TPH1 218A/C) demonstrating evidence for pleiotrophy. Another 12 meta-analyses of GWAS studies of the same disorders were identified, with no overlap in genetic variants reported. This review highlights the progress that is being made in identifying shared and unique genetic mechanisms that contribute to the risk of developing several major psychiatric disorders, and identifies further steps for progress.

Hypothesis exploration with visualization of variance

Background

The Consortium for Neuropsychiatric Phenomics (CNP) at UCLA was an investigation into the biological bases of traits such as memory and response inhibition phenotypes—to explore whether they are linked to syndromes including ADHD, Bipolar disorder, and Schizophrenia. An aim of the consortium was in moving from traditional categorical approaches for psychiatric syndromes towards more quantitative approaches based on large-scale analysis of the space of human variation. It represented an application of phenomics—wide-scale, systematic study of phenotypes—to neuropsychiatry research.

Results

This paper reports on a system for exploration of hypotheses in data obtained from the LA2K, LA3C, and LA5C studies in CNP. ViVA is a system for exploratory data analysis using novel mathematical models and methods for visualization of variance. An example of these methods is called VISOVA, a combination of visualization and analysis of variance, with the flavor of exploration associated with ANOVA in biomedical hypothesis generation. It permits visual identification of phenotype profiles—patterns of values across phenotypes—that characterize groups. Visualization enables screening and refinement of hypotheses about variance structure of sets of phenotypes.

Conclusions

The ViVA system was designed for exploration of neuropsychiatric hypotheses by interdisciplinary teams. Automated visualization in ViVA supports ‘natural selection’ on a pool of hypotheses, and permits deeper understanding of the statistical architecture of the data. Large-scale perspective of this kind could lead to better neuropsychiatric diagnostics.

The Dopamine D4 Receptor Gene (DRD4) Moderates Cultural Difference in Independent Versus Interdependent Social Orientation

Prior research suggests that cultural groups vary on an overarching dimension of independent versus interdependent social orientation, with European Americans being more independent, or less interdependent, than Asians. Drawing on recent evidence suggesting that the dopamine D4 receptor gene ( DRD4) plays a role in modulating cultural learning, we predicted that carriers of DRD4 polymorphisms linked to increased dopamine signaling (7- or 2-repeat alleles) would show higher levels of culturally dominant social orientations, compared with noncarriers. European Americans and Asian-born Asians (total N = 398) reported their social orientation on multiple scales. They were also genotyped for DRD4. As in earlier work, European Americans were more independent, and Asian-born Asians more interdependent. This cultural difference was significantly more pronounced for carriers of the 7- or 2-repeat alleles than for noncarriers. Indeed, no cultural difference was apparent among the noncarriers. Implications for potential coevolution of genes and culture are discussed.

The effect of neighborhood disadvantage, social ties, and genetic variation on the antisocial behavior of African American women: a multilevel analysis

Social disorganization theory posits that individuals who live in disadvantaged neighborhoods are more likely to engage in antisocial behavior than are those who live in advantaged neighborhoods and that neighborhood disadvantage asserts this effect through its disruptive impact on social ties. Past research on this framework has been limited in two respects. First, most studies have concentrated on adolescent males. In contrast, the present study focused on a sample of adult African American females. Second, past research has largely ignored individual-level factors that might explain why people who grow up in disadvantaged neighborhoods often do not engage in antisocial behavior. We investigated the extent to which genetic variation contributes to heterogeneity of response to neighborhood conditions. We found that the impact of neighborhood disadvantage on antisocial behavior was mediated by neighborhood social ties. Further, the analysis indicated that the effects of neighborhood disadvantage and social ties on antisocial behavior were moderated by genetic polymorphisms. Examination of these moderating effects provided support for the differential susceptibility model of Gene × Environment. The effect of Gene × Neighborhood Disadvantage on antisocial behavior was mediated by the effect of Gene × Neighborhood Social Ties, providing support for an expanded view of social disorganization theory.

Comparative Psychology as Unified Psychology: The Case of Curiosity and Other Novelty-Related Behavior

The comparative study of human and nonhuman animals covers the full range of psychological phenomenon, and so comparative psychology already exists as a form of general psychology. The potential of comparative psychology to bring together many aspects of the field of psychology is illustrated through a review of studies exploring curiosity in a variety of species. The issue of an organism's response to novelty was recognized as an important research subject in the era of Darwin. Since that time, considerable empirical and theoretical material on various aspects of behavior associated with new stimuli has been accumulated. This research additionally illustrates the utility of integrative levels theory, which enables a multilevel, comprehensive analysis of behavior. Comparative psychologists played important roles in the history of most of psychology's subdisciplines, and present-day comparative psychologists continue to contribute insights into a startlingly broad range of psychological phenomenon. Further, appreciation for the higher-level research program provided by comparative work provides a larger context that helps ground the study of human psychology.

The role of D4 receptor gene exon III polymorphisms in shaping human altruism and prosocial behavior

Human beings are an extraordinarily altruistic species often willing to help strangers at a considerable cost (sometimes life itself) to themselves. But as Darwin noted "… he who was ready to sacrifice his life, as many a savage has been, rather than betray his comrades, would often leave no offspring to inherit his noble nature." Hence, this is the paradox of altruism. Twin studies have shown that altruism and other prosocial behavior show considerable heritability and more recently a number of candidate genes have been identified with this phenotype. Among these first provisional findings are genes encoding elements of dopaminergic transmission. In this article we will review the evidence for the involvement of one of these, the dopamine D4 receptor (DRD4) gene, in shaping human prosocial behavior and consider the methodologies employed in measuring this trait, specific molecular genetic findings and finally, evidence from several Gene × Environment (G × E) studies that imply differential susceptibility of this gene to environmental influences.

Possible association of the DRD4 gene with a history of attention-deficit/hyperactivity disorder in women with bulimia nervosa

OBJECTIVE

Up to one-third of patients with bulimia nervosa (BN) report a history of attention-deficit/hyperactivity disorder (ADHD) symptoms, and the dopaminergic genes, especially the dopamine receptor D4 (DRD4), have been associated independently with both binge eating and ADHD.

METHOD

The purpose of this study was to (1) compare the frequency of DRD4 exon III VNTR variants in 157 BN probands and equal number of healthy controls; (2) assess transmission of DRD4 alleles in 68 families of patients with BN; and (3) explore the possible role of DRD4 gene in childhood ADHD history in a subgroup of 81 women with BN.

RESULTS

Our results showed that the BN probands and controls did not differ in DRD4 allele frequency. We also did not find evidence for preferential transmission of any DRD4 variant to the affected offspring with BN. However, the presence of either the 2-repeat or 7-repeat allele was associated with a history of childhood ADHD in BN (p = .038, odds ratio = 3.2).

DISCUSSION

Our findings suggest that although DRD4 may not be associated with the diagnosis of BN, its variants are associated with a history of childhood ADHD in BN probands. This may have relevance for the understanding, prevention, and treatment of BN that evolves in the context of childhood ADHD.

Dopamine D4 and D5 receptor gene variant effects on clozapine response in schizophrenia: replication and exploration

OBJECTIVES

This study aimed to: 1) replicate previously reported associations between dopamine D4 receptor gene (DRD4) polymorphisms and antipsychotic (AP) response in a clozapine (CLZ) response sample; and 2) explore possible associations of polymorphisms across dopamine D5 receptor gene (DRD5) as well as other DRD4 regions.

METHODS

DRD4 exon III 48-bp, intron I (G)(n), and 120-bp repeat polymorphisms, and three DRD4 single nucleotide polymorphisms (SNPs); and DRD5 (CA/CT/GT)(n) microsatellite and four DRD5 SNPs were assessed using standard genotyping and statistical procedures.

RESULTS

We report evidence, which does not survive correction for multiple testing, supporting previous DRD4 findings. Findings of interest include the 120-bp 1-copy allele, intron I (G)(n) 142-bp/140-bp genotype, and exon III 4R allele with CLZ response. All DRD5 tests were negative.

CONCLUSIONS

Overall, these results suggest a possible minor contribution of DRD4 variants, but not DRD5 variants, towards the AP/CLZ response phenotype.

Does the oxytocin receptor (OXTR) polymorphism (rs2254298) confer 'vulnerability' for psychopathology or 'differential susceptibility'? Insights from evolution

The diathesis-stress model of psychiatric conditions has recently been challenged by the view that it might be more accurate to speak of 'differential susceptibility' or 'plasticity' genes, rather than one-sidedly focusing on individual vulnerability. That is, the same allelic variation that predisposes to a psychiatric disorder if associated with (developmentally early) environmental adversity may lead to a better-than-average functional outcome in the same domain under thriving (or favourable) environmental conditions. Studies of polymorphic variations of the serotonin transporter gene, the monoamino-oxidase-inhibitor A coding gene or the dopamine D4 receptor gene indicate that the early environment plays a crucial role in the development of favourable versus unfavourable outcomes. Current evidence is limited, however, to establishing a link between genetic variation and behavioural phenotypes. In contrast, little is known about how plasticity may be expressed at the neuroanatomical level as a 'hard-wired' correlate of observable behaviour. The present review article seeks to further strengthen the argument in favour of the differential susceptibility theory by incorporating findings from behavioural and neuroanatomical studies in relation to genetic variation of the oxytocin receptor gene. It is suggested that polymorphic variation at the oxytocin receptor gene (rs2254298) is associated with sociability, amygdala volume and differential risk for psychiatric conditions including autism, depression and anxiety disorder, depending on the quality of early environmental experiences. Seeing genetic variation at the core of developmental plasticity can explain, in contrast to the diathesis-stress perspective, why evolution by natural selection has maintained such 'risk' alleles in the gene pool of a population.

Religion priming differentially increases prosocial behavior among variants of the dopamine D4 receptor (DRD4) gene

Building on gene-environment interaction (G × E) research, this study examines how the dopamine D4 receptor (DRD4) gene interacts with a situational prime of religion to influence prosocial behavior. Some DRD4 variants tend to be more susceptible to environmental influences, whereas other variants are less susceptible. Thus, certain life environments may be associated with acts of prosociality for some DRD4 variants but not others. Given that religion can act as an environmental influence that increases prosocial behavior, environmental input in the form of religion priming may have G × E effects. Results showed that participants with DRD4 susceptibility variants were more prosocial when implicitly primed with religion than not primed with religion, whereas participants without DRD4 susceptibility variants were not impacted by priming. This research has implications for understanding why different people may behave prosocially for different reasons and also integrates G × E research with experimental psychology.

Recent advances in the search for D3- and D4-selective drugs: probes, models and candidates

Dopamine D(2)-like receptors (including D(2), D(3) and D(4)) belong to the 'rhodopsin-like' family of G protein-coupled receptors (GPCRs), which represent the largest group of targets for bioactive molecules. Due to their high sequence similarity, the design of subtype-selective ligands requires rational and effective strategies. The general formula of 1,4-disubstituted aromatic piperidines and piperazines (1,4-DAPs) was extracted from classical dopaminergic drugs. The biological properties of this compound family are encoded by an aromatic head group that controls intrinsic activity, an amine moiety and a lipophilic appendage. D(3)- and D(4)-selective molecular probes and drug candidates were generated from the general formula of 1,4-DAP. Formal structural rearrangement led to investigational drugs beyond the 1,4-DAP structure. The very recent publication of the X-ray crystal structure of D(3) should facilitate efficient discovery of unprecedented chemotypes. However, the development of D(3)-selective agonists, functionally selective ligands and the exploitation of homo- and heteromers remain challenging.

Dopamine D4 receptor gene associated with fairness preference in ultimatum game

In experimental economics, the preference for reciprocal fairness has been observed in the controlled and incentivized laboratory setting of the ultimatum game, in which two individuals decide on how to divide a sum of money, with one proposing the share while the second deciding whether to accept. Should the proposal be accepted, the amount is divided accordingly. Otherwise, both would receive no money. A recent twin study has shown that fairness preference inferred from responder behavior is heritable, yet its neurogenetic basis remains unknown. The D4 receptor (DRD4) exon3 is a well-characterized functional polymorphism, which is known to be associated with attention deficit hyperactivity disorder and personality traits including novelty seeking and self-report altruism. Applying a neurogenetic approach, we find that DRD4 is significantly associated with fairness preference. Additionally, the interaction among this gene, season of birth, and gender is highly significant. This is the first result to link preference for reciprocal fairness to a specific gene and suggests that gene × environment interactions contribute to economic decision making.

Interaction between serotonin transporter promoter and dopamine receptor D4 polymorphisms on decision making

Appropriate decision making is an important brain function to maintain our lives. The Iowa gambling task (IGT) is a tool for decision making under ambiguity. The aims of this study were to evaluate the influence of serotonin transporter linked polymorphic region (5-HTTLPR) and dopamine receptor D4 (DRD4) polymorphisms and their interaction on IGT performance. One hundred fifty-nine normal subjects were involved in this study. All subjects performed the IGT and were genotyped for the triallelic 5-HTTLPR and DRD4 48 bp uVNTR polymorphisms. After controlling for gender, age, and impulsiveness, there were no main effects of 5-HTTLPR and DRD4 gene polymorphisms on total IGT score. However, there was a significant effect on the interaction between 5-HTTLPR and DRD4 on total IGT score. In the presence of the 5-HTTLPR S'S' (SS+SL(G)+L(G)L(G)), subjects with the DRD4 2R+ (2 repeat carrier) had higher total IGT score compared to those with the DRD4 2R-. In contrast, in the absence of the 5-HTTLPR S'S', subjects with the DRD4 2R- had higher total IGT score than those with the DRD4 2R+. When we divided IGT scores into the first and second half of trials, the 5-HTTLPRxDRD4 interaction effects were stronger in the second half block (decision under risk) than in the first half block (decision under ambiguity). In conclusion, the DRD4 genotypes might influence decision-making performance differently according to the background genotypes of 5-HTTLPR.

Incorporating genetics and genomics in risk assessment for inhaled manganese: from data to policy

Manganese is an essential nutrient, and a healthy human with good liver and kidney function can easily excrete excess dietary manganese. Inhaled manganese is a greater concern, because it bypasses the body's normal homeostatic mechanisms and can accumulate in the brain. Prolonged exposure to high manganese concentrations (>1mg/m(3)) in air leads to a Parkinsonian syndrome known as "manganism." Of greatest concern are recent studies which indicate that neurological and neurobehavioral deficits can occur when workers are exposed to much lower levels (<0.2mg/m(3)) of inhaled manganese in welding fumes. Consequently, researchers at NIOSH are conducting a risk assessment for inhaled manganese. Novel components of this risk assessment include an attempt to quantify the range of inter-individual differences using data generated by the Human Genome Project and experimental work to identify genetically based biomarkers of exposure, disease and susceptibility. The difficulties involved in moving from epidemiological and in vivo data to health-based quantitative risk assessment and ultimately enforceable government standards are discussed.

Genetic variants of D2 but not D3 or D4 dopamine receptor gene are associated with rapid onset and poor prognosis of methamphetamine psychosis

D2-like receptors are key targets for methamphetamine in the CNS, and their activation is an initial and indispensable effect in the induction of dependence and psychosis. It is possible that genetic variants of D2-like receptors may affect individual susceptibility to methamphetamine dependence and psychosis. To test this hypothesis, 6 putatively functional polymorphisms of D2-like receptors, -141C Ins/Del, Ser311Cys and TaqIA of the DRD2 gene, Ser9Gly of the DRD3 gene, and -521C>T and a variable number of tandem repeats in exon 3 of the DRD4 gene, were analyzed in 202 patients with methamphetamine dependence and/or psychosis and 243 healthy controls in a Japanese population. No polymorphism examined showed significant association with methamphetamine dependence, but two polymorphisms of DRD2 were associated with the clinical course and prognosis of methamphetamine psychosis. The A1/A1 homozygote of DRD2 was a negative risk factor for a poorer prognosis of psychosis that continues for more than 1 month after the discontinuance of methamphetamine abuse and the beginning of treatment with neuroleptics (p=0.04, odds ratio (OR)=0.42, 95% CI; 0.27-0.65) and the complication of spontaneous relapse of methamphetamine psychosis after remission (p=0.014, OR=0.34, 95% CI; 0.22-0.54). The genotype of -141C Del positive (Del/Del and Del/Ins) was at risk for rapid onset of methamphetamine psychosis that develops into a psychotic state within 3 years after initiation of methamphetamine abuse (p=0.00037, OR=3.62, 95% CI 2.48-5.28). These findings revealed that genetic variants of DRD2, but not DRD3 or DRD4, confer individual risks for rapid onset, prolonged duration, and spontaneous relapse of methamphetamine psychosis.

The DRD4 exon 3 VNTR polymorphism and addiction-related phenotypes: a review

In addition to the large literatures on associations of the DRD4 VNTR polymorphism with ADHD and personality traits, there is an emerging literature linking this variant to addiction and addiction-related phenotypes. When only diagnosis-based studies are considered, an inconsistent picture emerges raising doubts as to the relevance of this polymorphism to addiction. However the use of multiple levels of analysis in examining the importance of this polymorphism has raised the possibility of an urge-related "intermediate phenotype" that puts one at risk for developing addiction but may not be found in all persons with an addiction diagnosis. From cellular assays through neuroimaging and behavioral phenotypes, these studies highlight the power of the "intermediate phenotype" approach and suggest a possible explanation of the mixed findings when diagnosis is used as the phenotype. Strengths and weaknesses of alternative DRD4 VNTR genotype grouping strategies are discussed. In sum, converging evidence across multiple methodologies supports the possibility of a robust relationship between the DRD4 exon 3 VNTR polymorphism and urge for addictive substances.

The association of 5-HTTLPR and DRD4 VNTR polymorphisms with affective temperamental traits in healthy volunteers

BACKGROUND

There has been growing evidence that temperamental traits, including affective temperaments, are heritable and associated with genetic polymorphisms. The purpose of the present study was to investigate the possible relationship between affective temperaments and the triallelic serotonin transporter gene-linked polymorphic region (5-HTTLPR) and dopamine receptor D4 (DRD4) polymorphisms in healthy Korean subjects.

METHODS

Three hundred thirty-five healthy college students were recruited, and 290 participants with a complete data set (172 males, 118 females) were included in the data analysis. The DNA of the subjects was isolated from whole blood cells, and the 5-HTTLPR and DRD4 variable number of tandem repeats polymorphisms were genotyped using polymerase chain reaction. Participants performed the 110-item version of the Temperament Evaluation of Memphis, Pisa, Paris, and San Diego auto-questionnaire (TEMPS-A) measuring five affective temperamental traits.

RESULTS

A significant association was found between the DRD4 polymorphism and the cyclothymic and irritable temperaments in male subjects. No significant association was shown between the 5-HTTLPR gene polymorphisms and affective temperaments.

LIMITATION

Our data were collected from a specific group of college students and cannot be generalized easily to other non-clinical populations. In addition, Korean version of the TEMPS-A used in this study has not yet been validated in Korean population.

CONCLUSIONS

This study showed a possible association between the DRD4 polymorphism and certain affective temperaments in the Korean male population. The clarification of the biological basis of predisposing temperaments such as cyclothymic temperament might help to understand the pathophysiology and mechanisms of mood disorders.