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1.  Mu opioid receptor (OPRM1) as a predictor of treatment outcome in opiate-dependent individuals of Arab descent 
A number of research studies on the genetics of opiate dependence have focused on the μ-opioid receptor (OPRM1), which is a primary target for opiates. This study aims to identify genetic polymorphisms within the OPRM1 gene involved in response to the biopsychosocial treatment in opiate-dependent individuals of Arab descent.
Unrelated Jordanian Nationals of Arab descent (N = 183) with opiate dependence were selected for this study. These individuals, all males, met the DSM-IV criteria for opiate dependence and were undergoing a voluntary 8-week treatment program at a Jordanian Drug Rehabilitation Centre. All individuals were genotyped for 22 single nucleotide polymorphisms (SNPs) within the OPRM1 gene using the Sequenom MassARRAY® system (iPLEX GOLD). Statistical analyses were carried out using the R package.
Patients receiving biopsychosocial treatment showed that there was a significant difference in their OPRM1 SNPs’ genotyping distribution between good, moderate, and poor responders to the treatment at two sites (rs6912029 [G-172T], and rs12205732 [G-1510A], P < 0.05, Fisher’s exact test).
This study is the first report of an association between the OPRM1 G-172T and G-1510A polymorphisms and treatment response for opiate dependence. Specifically, this study demonstrated that the OPRM1 GG-172 and GG-1510 genotypes were more frequent among patients who were nonresponders to the biopsychosocial treatment. However, further pharmacogenetic studies in a larger cohort of opiate-dependent patients of Arab descent are needed to confirm these findings and identify individuals with increased chance of relapse.
PMCID: PMC3513232  PMID: 23226066
OPRM1; association; opiates; dependence; treatment response; Arab
2.  Association of dopaminergic pathway gene polymorphisms with chronic renal insufficiency among Asian Indians with type-2 diabetes 
BMC Genetics  2008;9:26.
Genetic markers conferring susceptibility to diabetes specific renal disease remains to be identified for early prediction and development of effective drugs and therapies. Inconsistent results obtained from analysis of genes from classical pathways generate need for examination of unconventional genetic markers having role in regulation of renal function. Experimental and clinical evidences suggest that dopamine is an important natriuretic hormone. Therefore, various genes involved in regulation of dopamine bioavailability could play a role in diabetic chronic renal insufficiency (CRI). We investigated the contribution of 12 polymorphisms from five Dopaminergic pathway genes to CRI among type-2 diabetic Asian Indian subjects.
Genetic association of 12 polymorphisms (SNPs) from five genes namely-dopamine receptor-1 (DRD1), DRD2, DRD3, DRD4, andcatechol-O-methyltransferase (COMT) with diabetic CRI was investigated using a case-control approach. Logistic regression analysis was carried out to correlate various clinical parameters with genotypes, and to study pair wise interactions between SNPs of different genes.
SNPs -141 ins/del C and G>A (1 kb upstream from exon 2) in DRD2 gene showed significant allelic and genotypic association. Allele -141 insC and genotype -141 insC/insC of -141 ins/del C polymorphism, and allele A of G>A SNP were found to be predisposing to CRI. Our result of allelic and genotypic association of -141 insC/delC SNP was also reflected in the haplotypic association. Heterozygous genotype of polymorphism 900 ins/del C in COMT gene was predisposing towards CRI.
Some polymorphisms in DRD2 and COMT genes are significantly associated with susceptibility to CRI in the Asian Indian population which, if confirmed would be consistent with a suggested role of dopamine metabolism in disease occurrence.
PMCID: PMC2287188  PMID: 18366720
3.  Associations between DRDs and schizophrenia in a Korean population: multi-stage association analyses 
The dysregulation of the dopaminergic system has been implicated in the pathophysiology of major psychosis, including schizophrenia, with dopamine receptor genes (DRDs) presently targeted as the most promising candidate genes. We investigated DRD1-5 for association with schizophrenia using a multi-stage approach in a Korean sample. One hundred forty-two SNPs in DRD1-5 were selected from the dbSNP, and the associations of each SNP were then screened and typed by MALDI-TOF mass spectrometry using pooled DNA samples from 150 patients with major psychosis and 150 controls. Each of the suggested SNPs was then genotyped and tested for an association within the individual samples comprising each pool. Finally, the positively associated SNPs were genotyped in an extended sample of 270 patients with schizophrenia and 350 controls. Among the 142 SNPs, 88 (62%) SNPs in our Korean population were polymorphic. At the pooling stage, 10 SNPs (DRD1: 2, DRD2: 3, and DRD4: 5) were identified (P < 0.05). SNPs rs1799914 of DRD1 (P = 0.046) and rs752306 of DRD4 (P = 0.017) had significantly different allele frequencies in the individually genotyped samples comprising the pool. In the final stage, with the extended sample, the suggestive association of DRD4 with rs752306 was lost, but the association of DRD1 with rs1799914 gained greater significance (P = 0.017). In these large-scale multi-stage analyses, we were able to find a possible association between DRD1 and schizophrenia. These findings suggested the potential contribution of a multi-step strategy for finding genes related to schizophrenia.
PMCID: PMC3041937  PMID: 21178390
Asian continental ancestry group; gene pool; genetic association studies; receptors, dopamine; schizophrenia
4.  Dopamine receptor D1 and post-synaptic density gene variants associate with opiate abuse and striatal expression levels 
Molecular psychiatry  2012;18(11):10.1038/mp.2012.140.
Opioid drugs are highly addictive and their abuse has a strong genetic load. Dopamine-glutamate interactions are hypothesized to be important for regulating neural systems central for addiction vulnerability. Balanced dopamine-glutamate interaction is mediated through several functional associations, including a physical link between discs, large homolog 4 (Drosophila) (DLG4, PSD-95) and dopamine receptor 1 (DRD1) within the postsynaptic density to regulate DRD1 trafficking. To address whether genetic associations with heroin abuse exist in relation to dopamine and glutamate and their potential interactions, we evaluated single nucleotide polymorphisms of key genes within these systems in three populations of opiate abusers and controls, totaling 489 individuals from Europe and the USA. Despite significant differences in racial makeup of the separate samples, polymorphisms of DRD1 and DLG4 were found to be associated with opiate abuse. In addition, a strong gene-gene interaction between homer 1 homolog (Drosophila) (HOMER1) and DRD1 was predicted to occur in Caucasian subjects. This interaction was further analyzed by evaluating DRD1 genotype in relation to HOMER1b/c protein expression in postmortem tissue from a subset of Caucasian subjects. DRD1 rs265973 genotype correlated with HOMER1b/c levels in the striatum, but not cortex or amgydala; the correlation was inversed in opiate abusers as compared to controls. Cumulatively, these results support the hypothesis that there may be significant, genetically-influenced interactions between glutamatergic and dopaminergic pathways in opiate abusers.
PMCID: PMC3637428  PMID: 23044706
addiction; heroin; epistasis; post mortem; striatum; plasticity; glutamate
5.  Polymorphisms of DRD2 and DRD3 genes and Parkinson’s disease: A meta-analysis 
Biomedical Reports  2014;2(2):275-281.
Parkinson’s disease (PD) is the second most common neurodegenerative disorder that affects ~2% of the population aged ≥65 years. The degeneration of dopamine neurons in the substantia nigra contributes to the pathogenesis of PD. Dopamine receptor D2 (DRD2) and dopamine receptor D3 (DRD3) are two key subtypes of dopamine receptors. The aim of our study was to evaluate the association between the polymorphisms of DRD2 and DRD3 genes and PD. Meta-analyses were conducted from 16 studies (46 stages) among 4,279 cases and 5,661 controls between PD and 9 polymorphisms (DRD2: rs1800497, rs1079597, rs6278, rs6279, rs273482, rs1799732 and rs1076563; DRD3: rs6280 and rs2134655). A significant association was observed between DRD3 rs2134655 polymorphism and PD [P=0.01, odds ratio (OR)=1.17, 95% confidence interval (CI): 1.03–1.32] and a borderline association was observed between DRD2 rs1800497 polymorphism and PD in Europeans (P=0.05, OR=1.13, 95% CI: 1.00–1.27). Findings of the current meta-analysis suggested that DRD3 rs2134655 polymorphism was associated with a 17% increased risk of PD and that DRD2 rs1800497 polymorphism had a potential to increase the risk of PD by 13% in Europeans. Future large-scale studies are required to confirm the ethnic difference of DRD2 rs1800497 polymorphism and to determine whether there were significant associations of PD with other polymorphisms in DRD2 and DRD3 genes.
PMCID: PMC3917740  PMID: 24649110
Parkinson; polymorphism; meta-analysis; dopamine receptor D2; dopamine receptor D3
6.  Associations of the Dopamine D4 Receptor Gene VNTR Polymorphism with Drug Use in Adolescent Psychiatric Inpatients 
The VNTR polymorphism in the Dopamine D4 receptor gene (DRD4) has been associated with differential urge for substances across multiple methodologies ranging from neuroimaging to assessment in the natural environment. It is unclear whether the DRD4 gene is a marker for an underlying propensity for greater urge or whether the DRD4 gene differentially moderates the neuroadaptive effects of extended substance use on urge. Examination of the DRD4 in an adolescent sample may provide evidence of a mechanism of this putative relationship.
Data from a subset of 77 participants in a larger assessment study characterized adolescents for substance-related behaviors by DRD4 genotype. The psychiatrically admitted adolescents were genotyped for the variable number of tandem repeats polymorphism in the DRD4 gene (L ≥ 7 [n = 25], S = < 7 [n = 52]). Associations of the DRD4 with scores on the SASSI, and ADI were examined as well as selected individual items thought to be most related to the intermediate phenotype of urge.
The DRD4 gene was not associated with any DSM-IV substance misuse diagnostic classification. Individual items related to urge were also nonsignificantly related to DRD4 status. Carriers of the long variant of the DRD4 polymorphism were more likely to have used hard drugs within the previous 6 months and scored higher on the self-medication subscale of the ADI compared to short variant homozygotes.
Preliminary results provide little evidence for the DRD4 VNTR polymorphism to be related to urge-related phenomena in hospitalized adolescents on a psychiatric inpatient unit. The association of the DRD4 gene with hard drug use may support literature linking this gene to impulsivity. Subscale findings may suggest a role of negative affect in previous DRD4 urge findings.
PMCID: PMC1864953  PMID: 17175015
DRD4; adolescents; substance misuse
7.  Dopamine D2 Receptor Polymorphisms and Adenoma Recurrence in the Polyp Prevention Trial 
Epidemiological evidence suggests that obesity may be causally associated with colorectal cancer. Dopamine and the dopaminergic reward pathway have been implicated in drug and alcohol addiction as well as obesity. Polymorphisms within the D2 dopamine receptor gene (DRD2) have been shown to be associated with colorectal cancer risk.
We investigated the association between DRD2 genotype at these loci and the risk of colorectal adenoma recurrence in the Polyp Prevention Trial. Odds ratios (OR) and 95% confidence intervals (CI) for risk of adenoma recurrence were calculated using unconditional logistic regression. Individuals with any, multiple (≥2) or advanced adenoma recurrence after 4 years were compared to those without adenoma recurrence. Variation in intake of certain dietary components according to DRD2 genotype at 3 loci (rs1799732; rs6277; rs1800497) was also investigated.
The DRD2 rs1799732 CT genotype was significantly associated with all adenoma recurrence (OR: 1.30; 95% CI: 1.01, 1.69). The rs1800497 TT genotype was also associated with a significantly increased risk of advanced adenoma recurrence (OR: 2.40; 95% CI: 1.11, 5.20).
The rs1799732 CT and rs1800497 TT genotypes were significantly associated with adenoma recurrence in the Polyp Prevention Trial. Increased risk of adenoma recurrence as conferred by DRD2 genotypes may be related to difference in alcohol and fat intake across genotypes.
PMCID: PMC2768275  PMID: 19065655
8.  Case–control association analysis of Dopamine receptor polymorphisms in alcohol dependence: a pilot study in Indian males 
BMC Research Notes  2013;6:418.
Brain imaging studies and knock-out animal models have derived substantial abetment for dopamine receptor (DR) subtypes as potential candidates in susceptibility to addictive disorders, including alcohol dependence (AD). Various association studies that compared the frequencies of alleles of the dopamine D1, D2, D3 and D4 receptor genes between alcohol dependent and control subjects have produced suggestive results, though some of them are discordant in nature. In the absence of genetic data from Indian population, we evaluated genetic association of three polymorphisms namely rs4532 in DRD1, rs6280 in DRD3 and 120 bp duplication in 1.2 kb upstream region of DRD4 with AD.
A total of 90 cases (alcohol dependent males) and 122 age and ethnicity matched healthy male controls were recruited in the study by following DSM-IV criteria. Three polymorphisms, namely rs4532 in DRD1, rs6280 in DRD3 and 120 bp duplication in 1.2 kb upstream region of DRD4 were selected (based on minor allele frequency and available literature) for genotyping by PCR-RFLP/LP method. Allele and genotype frequencies of these genetic markers were compared using Pearson’s χ2 test followed by risk assessment using odds ratio. Statistical analysis of clinical parameters such as AUDIT scores of case subjects was also performed.
Statistically significant associations of polymorphisms in DRD1 and DRD4 with alcoholism were found.
Our results underscore that genetic variations in dopamine receptors D1 and D4 may influence genetic predisposition to alcoholism. Unavailability of comparative data from Indian population and small sample size necessitate replication of results in an independent cohort.
PMCID: PMC3853477  PMID: 24135011
Alcohol dependence; Dopamine receptors; Polymorphisms; Case–control study; Genetic association
9.  Association between dopaminergic polymorphisms and borderline personality traits among at-risk young adults and psychiatric inpatients 
In the development of borderline personality disorder (BPD) both genetic and environmental factors have important roles. The characteristic affective disturbance and impulsive aggression are linked to imbalances in the central serotonin system, and most of the genetic association studies focused on serotonergic candidate genes. However, the efficacy of dopamine D2 receptor (DRD2) blocking antipsychotic drugs in BPD treatment also suggests involvement of the dopamine system in the neurobiology of BPD.
In the present study we tested the dopamine dysfunction hypothesis of impulsive self- and other-damaging behaviors: borderline and antisocial traits were assessed by Structured Clinical Interview for Diagnosis (SCID) for DSM-IV in a community-based US sample of 99 young adults from low-to-moderate income families. For the BPD trait analyses a second, independent group was used consisting of 136 Hungarian patients with bipolar or major depressive disorder filling out self-report SCID-II Screen questionnaire. In the genetic association analyses the previously indicated polymorphisms of the catechol-O-methyl-transferase (COMT Val158Met) and dopamine transporter (DAT1 40 bp VNTR) were studied. In addition, candidate polymorphisms of the DRD2 and DRD4 dopamine receptor genes were selected from the impulsive behavior literature.
The DRD2 TaqI B1-allele and A1-allele were associated with borderline traits in the young adult sample (p = 0.001, and p = 0.005, respectively). Also, the DRD4 -616 CC genotype appeared as a risk factor (p = 0.02). With severity of abuse accounted for in the model, genetic effects of the DRD2 and DRD4 polymorphisms were still significant (DRD2 TaqIB: p = 0.001, DRD2 TaqIA: p = 0.008, DRD4 -616 C/G: p = 0.002). Only the DRD4 promoter finding was replicated in the independent sample of psychiatric inpatients (p = 0.007). No association was found with the COMT and DAT1 polymorphisms.
Our results of the two independent samples suggest a possible involvement of the DRD4 -616 C/G promoter variant in the development of BPD traits. In addition, an association of the DRD2 genetic polymorphisms with impulsive self-damaging behaviors was also demonstrated.
PMCID: PMC2823641  PMID: 20205808
10.  HIV-related cognitive impairment shows bi-directional association with dopamine receptor DRD1 and DRD2 polymorphisms in substance dependent and independent populations 
Journal of neurovirology  2013;19(5):10.1007/s13365-013-0204-8.
It has been postulated that drugs of abuse act synergistically with HIV, leading to increased neurotoxicity and neurocognitive impairment. The CNS impacts of HIV and drug use converge on the mesocorticolimbic dopamine (DA) system, which contains two main receptor subtypes: dopamine receptor 1 and 2. (DRD1, DRD2). DRD1 and DRD2 have been linked to substance dependence; whether they predict HIV-associated neurocognitive disorder (HAND) is unclear. Using an advanced-stage HIV+ population, we sought to determine if drug dependence impacts the contribution of DA receptor polymorphisms on neurocognition. We observed that both DRD1 and DRD2 polymorphisms were associated with opiate and cocaine dependence (P<0.05) in Caucasian subjects, but not African-American individuals. Using linear regression analysis, we examined the polymorphisms for associations with neuropsychological performance in global and cognitive domain T-scores (Motor, Processing Speed, Verbal Fluency, Learning, Memory, Executive Functioning, Working Memory) while controlling for opiate and cocaine dependency. In the Motor domain, we observed an association for two DRD2 polymorphisms (P<0.05) in Caucasian subjects. The effects differed for substance dependence groups as the direction of the correlations with DRD2 were opposite to what was seen in subjects without these dependencies. In African-American subjects, associations were observed in nearly every domain and again, the direction of the correlation differed between substance dependent and independent groups. We conclude that studies to examine genetic risk for HAND must carefully account for substance dependence patterns when assaying dopaminergic systems, as the neurobiological substrates of cognition in HIV populations may vary with tonic alterations secondary to chronic substance exposures.
PMCID: PMC3856629  PMID: 24078558
HAND; cocaine; opiate; SNP
11.  Dopamine receptor genetic polymorphisms and body composition in undernourished pastoralists: An exploration of nutrition indices among nomadic and recently settled Ariaal men of northern Kenya 
Minor alleles of the human dopamine receptor polymorphisms, DRD2/TaqI A and DRD4/48 bp, are related to decreased functioning and/or numbers of their respective receptors and have been shown to be correlated with body mass, height and food craving. In addition, the 7R minor allele of the DRD4 gene is at a higher frequency in nomadic compared to sedentary populations. Here we examine polymorphisms in the DRD2 and DRD4 genes with respect to body mass index (BMI) and height among men in two populations of Ariaal pastoralists, one recently settled (n = 87) and the other still nomadic (n = 65). The Ariaal live in northern Kenya, are chronically undernourished and are divided socially among age-sets.
Frequencies of the DRD4/7R and DRD2/A1 alleles were 19.4% and 28.2%, respectively and did not differ between the nomadic and settled populations. BMI was higher in those with one or two DRD4/7R alleles in the nomadic population, but lower among the settled. Post-hoc analysis suggests that the DRD4 differences in BMI were due primarily to differences in fat free body mass. Height was unrelated to either DRD2/TaqI A or DRD4/48 bp genotypes.
Our results indicate that the DRD4/7R allele may be more advantageous among nomadic than settled Ariaal men. This result suggests that a selective advantage mediated through behaviour may be responsible for the higher frequency of the 7R alleles in nomadic relative to sedentary populations around the world. In contrast to previous work, we did not find an association between DRD2 genotypes and height. Our results support the idea that human phenotypic expression of genotypes should be rigorously evaluated in diverse environments and genetic backgrounds.
PMCID: PMC2440754  PMID: 18544160
12.  Genetic variants associated with addictive behavior in Colombian addicted and non-addicted to heroin or cocaine 
Colombia Médica : CM  null;44(1):19-25.
Determine the prevalence and compare some genetic markers involved in addictive behavior in a group of addicts to derivative of coca (cocaine/crack) or heroin and a control group of non-addicted people matched for gender, age and ethnicity.
A 120 addicts and 120 non-addicts Colombian male were surveyed and genotyped for 18 polymorphism of the OPRM1, DRD2, DRD4, SLC6A3, SLC6A4, ABCB1, DβH and CYP2B6 genes. For the identification of alleles markers were used mini-sequencing and fragment multiplex PCR techniques; ethnicity of cases and controls was analyzed with 61 AIMs.
The age of onset use of heroin or coca derivatives (cocaine/crack) was 16.5±6 years and 99.2% of them consume several illicit drugs. It showed that controls and addicts belong to the same ethnic group. Significant differences between addicts and controls in relation to schooling, marital status, social security family history of substance abuse (p <0.001), Int8-VNTR SLC6A3 gene (p= 0.015) and SNP 3435C>T ABCB1 gene (p= 0.001) were found.
The present results indicate that the VNTR- 6R polymorphism of the gene SLC6A3 and the genotype 3435CC in the ABCB1 gene, are both associated with addictive behavior to heroin or cocaine.
PMCID: PMC4002011  PMID: 24892317
ABCB1 Protein; SLC6A3 protein; heroin addiction; cocaine addiction; c-rack-cocaine
13.  DRD2 polymorphisms modulate reward and emotion processing, dopamine neurotransmission and openness to experience 
Dopamine (DA) neurotransmission through D2 receptors (DRD2) has been implicated in the regulation of reward processing, cognition and the effects of drugs of abuse, and also has significant effects in responses to stressors and salient aversive stimuli. An examination of the influence of genetic variation across multiple psychophysical measures therefore appears critical to understand the neurobiology of DA-modulated complex personality traits and psychiatric illnesses. To examine interindividual variation in the function of DRD2 modulated mechanisms in healthy humans, we used a haplotype-based and single nucleotide polymorphism (SNP) investigation. Their effects were interrogated with functional magnetic resonance imaging (fMRI) during reward and emotional processing. We found that a haplotype block composed by two SNPs, rs4274224 and rs4581480, affected the hemodynamic responses of the dorsolateral prefrontal cortex (DLPFC) during reward expectation and the subgenual anterior cingulate cortices (sgACC) during implicit emotional processing. Exploratory analysis within the significant haplotype block revealed the same functional effects only for the SNP rs4274224. Further analysis on rs4274224 using functional connectivity and positron emission tomography (PET) measures of DA D2/3 receptor mediated neurotransmission confirmed a gene effect on the functional connectivity of the DLPFC during reward anticipation and subcortical stress induced dopamine release. At a phenotypic trait level, significant effects of genotype were obtained for the NEO PI-R “Openness to Experience” and further correlated with neuroimaging data. Overall, these results show significant neurobiological effects of genotype variation in DRD2 on multiple functional domains, such as emotional, stress and reward processing. As such, it contributes to normal variation and potentially to vulnerability to psychopathology associated with those functions, such as risk for mood and substance use disorders.
PMCID: PMC3381848  PMID: 22424959
imaging; dopamine; DLPFC; reward; emotion
14.  Drd4 gene polymorphisms are associated with personality variation in a passerine bird 
Polymorphisms in several neurotransmitter-associated genes have been associated with variation in human personality traits. Among the more promising of such associations is that between the human dopamine receptor D4 gene (Drd4) variants and novelty-seeking behaviour. However, genetic epistasis, genotype–environment interactions and confounding environmental factors all act to obscure genotype–personality relationships. Such problems can be addressed by measuring personality under standardized conditions and by selection experiments, with both approaches only feasible with non-human animals. Looking for similar Drd4 genotype–personality associations in a free-living bird, the great tit (Parus major), we detected 73 polymorphisms (66 SNPs, 7 indels) in the P. major Drd4 orthologue. Two of the P. major Drd4 gene polymorphisms were investigated for evidence of association with novelty-seeking behaviour: a coding region synonymous single nucleotide polymorphism (SNP830) and a 15 bp indel (ID15) located 5′ to the putative transcription initiation site. Frequencies of the three Drd4 SNP830 genotypes, but not the ID15 genotypes, differed significantly between two P. major lines selected over four generations for divergent levels of ‘early exploratory behaviour’ (EEB). Strong corroborating evidence for the significance of this finding comes from the analysis of free-living, unselected birds where we found a significant association between SNP830 genotypes and differing mean EEB levels. These findings suggest that an association between Drd4 gene polymorphisms and animal personality variation predates the divergence of the avian and mammalian lineages. Furthermore, this work heralds the possibility of following microevolutionary changes in frequencies of behaviourally relevant Drd4 polymorphisms within populations where natural selection acts differentially on different personality types.
PMCID: PMC1914334  PMID: 17472912
personality; Drd4; dopamine receptor; polymorphisms; Parus major; novelty seeking
15.  Evaluation of Genetic Variability in the Dopamine Receptor D2 in Relation to Behavioral Inhibition and Impulsivity/Sensation Seeking: An Exploratory Study With d-Amphetamine in Healthy Participants 
The dopamine D2 receptor (DRD2) appears to be involved in impulsive behaviors, and particularly in behavioral inhibition. We sought to determine whether inhibition and impulsivity were related to genetic polymorphisms in the DRD2 gene (DRD2) in healthy volunteers (N = 93). Participants received placebo or d-amphetamine in random order. They performed the stop task, measuring behavioral inhibition, and rated their mood states on each session. They also completed the Zuckerman–Kuhlman Personality Questionnaire, including an Impulsivity subscale. We investigated the association between 12 single nucleotide polymorphisms (SNPs) and haplotypes in DRD2 and stop task performance in the nondrug (i.e., placebo) session and on the personality measure of impulsivity. We secondarily evaluated the DRD2 SNPs in relation to response to d-amphetamine on stop task performance and mood ratings. Mood was not related to genotypes in either the drug free condition or in response to drug. However, 2 SNPs, rs4648317 and rs12364283, and a haplotype block consisting of those SNPs, were associated with better performance on the stop task in the drug free condition and lower scores on the Impulsivity subscale. We also found that rs12364283 was associated with effects of d-amphetamine on stop task performance: d-amphetamine decreased stop reaction time (RT) in the A/A group but increased stop RT in the combined A/G + G/G genotype. Of the SNPs we evaluated, rs12364283, which has been associated with DRD2 expression, was the most significantly associated with inhibition and impulsivity. The significant relationship between DRD2 genotype and both behavioral inhibition and impulsivity suggests a possible common genetic influence on behavioral and self-report measures of impulsivity.
PMCID: PMC2879583  PMID: 19968402
DRD2; inhibition; impulsivity; amphetamine; Stop Task
16.  Multivariate Analysis of Dopaminergic Gene Variants as Risk Factors of Heroin Dependence 
PLoS ONE  2013;8(6):e66592.
Heroin dependence is a debilitating psychiatric disorder with complex inheritance. Since the dopaminergic system has a key role in rewarding mechanism of the brain, which is directly or indirectly targeted by most drugs of abuse, we focus on the effects and interactions among dopaminergic gene variants.
To study the potential association between allelic variants of dopamine D2 receptor (DRD2), ANKK1 (ankyrin repeat and kinase domain containing 1), dopamine D4 receptor (DRD4), catechol-O-methyl transferase (COMT) and dopamine transporter (SLC6A3) genes and heroin dependence in Hungarian patients.
303 heroin dependent subjects and 555 healthy controls were genotyped for 7 single nucleotide polymorphisms (SNPs) rs4680 of the COMT gene; rs1079597 and rs1800498 of the DRD2 gene; rs1800497 of the ANKK1 gene; rs1800955, rs936462 and rs747302 of the DRD4 gene. Four variable number of tandem repeats (VNTRs) were also genotyped: 120 bp duplication and 48 bp VNTR in exon 3 of DRD4 and 40 bp VNTR and intron 8 VNTR of SLC6A3. We also perform a multivariate analysis of associations using Bayesian networks in Bayesian multilevel analysis (BN-BMLA).
Findings and conclusions
In single marker analysis the TaqIA (rs1800497) and TaqIB (rs1079597) variants were associated with heroin dependence. Moreover, –521 C/T SNP (rs1800955) of the DRD4 gene showed nominal association with a possible protective effect of the C allele. After applying the Bonferroni correction TaqIB was still significant suggesting that the minor (A) allele of the TaqIB SNP is a risk component in the genetic background of heroin dependence. The findings of the additional multiple marker analysis are consistent with the results of the single marker analysis, but this method was able to reveal an indirect effect of a promoter polymorphism (rs936462) of the DRD4 gene and this effect is mediated through the –521 C/T (rs1800955) polymorphism in the promoter.
PMCID: PMC3696122  PMID: 23840506
17.  Heroin addiction in African Americans: a hypothesis-driven association study 
Genes, brain, and behavior  2009;8(5):531-540.
Heroin addiction is a chronic complex disease with a substantial genetic contribution. This study was designed to identify gene variants associated with heroin addiction in African Americans. The emphasis was on genes involved in reward modulation, behavioral control, cognitive function, signal transduction, and stress response. We have performed a case-control association analysis by screening with 1350 variants of 130 genes. The sample consisted of 202 former severe heroin addicts in methadone treatment and 167 healthy controls with no history of drug abuse. Single-SNP, haplotype and multi-SNP genotype pattern analyses were performed. Seventeen SNPs showed point-wise significant association with heroin addiction (nominal P < 0.01). These SNPs are from genes encoding several receptors: adrenergic (ADRA1A), arginine vasopressin (AVPR1A), cholinergic (CHRM2), dopamine (DRD1), GABA-A (GABRB3), glutamate (GRIN2A), and serotonin (HTR3A), as well as alcohol dehydrogenase (ADH7), glutamic acid decarboxylase (GAD1 and GAD2), the nucleoside transporter (SLC29A1), and diazepam binding inhibitor (DBI). The most significant result of the analyses was obtained for the GRIN2A haplotype G-A-T (rs4587976-rs1071502-rs1366076) with protective effect (P uncorrected = 9.6E-05, P corrected = 0.058). This study corroborates several reported associations with alcohol and drug addiction as well as other related disorders, and extends the list of variants that may affect the development of heroin addiction. Further studies will be necessary to replicate these associations and to elucidate the roles of these variants in drug addiction vulnerability.
PMCID: PMC2716061  PMID: 19500151
association study; heroin addiction; polymorphisms; African Americans; NMDA glutamate receptor
18.  Association of COMT and COMT-DRD2 interaction with creative potential 
Several lines of evidence suggest that genes involved in dopamine (DA) transmission may contribute to creativity. Among these genes, the catechol-O-methyltransferase gene (COMT) and the dopamine D2 receptor gene (DRD2) are the most promising candidates. Our previous study has revealed evidence for the involvement of DRD2 in creative potential. The present study extended our previous study by systematically exploring the association of COMT with creative potential as well as the interaction between COMT and DRD2. Twelve single nucleotide polymorphisms (SNPs) covering COMT were genotyped in 543 healthy Chinese college students whose creative potentials were assessed by divergent thinking tests. Single SNP analysis showed that rs174697 was nominally associated with verbal originality, two SNPs (rs737865 and rs5993883) were nominally associated with figural fluency, and two SNPs (rs737865 and rs4680) were nominally associated with figural originality. Haplotype analysis showed that, the TCT and CCT haplotype (rs737865-rs174675-rs5993882) were nominally associated with figural originality, and the TATGCAG and CGCGGGA haplotype (rs4646312-rs6269-rs4633-rs6267-rs4818-rs4680-rs769224) were nominally associated with figural originality and verbal flexibility, respectively. However, none of these nominal findings survived correction for multiple testing. Gene–gene interaction analysis identified one significant four-way interaction of rs174675 (COMT), rs174697 (COMT), rs1076560 (DRD2), and rs4436578 (DRD2) on verbal fluency, one significant four-way interaction of rs174675 (COMT), rs4818 (COMT), rs1076560 (DRD2), and rs4648317 (DRD2) on verbal flexibility, and one significant three-way interaction of rs5993883 (COMT), rs4648319 (DRD2), and rs4648317 (DRD2) on figural flexibility. In conclusion, the present study provides nominal evidence for the involvement of COMT in creative potential and suggests that DA related genes may act in coordination to contribute to creativity.
PMCID: PMC3995040  PMID: 24782743
creativity; creative potential; divergent thinking; dopamine; COMT; DRD2; gene–gene interaction
19.  Association of Dopamine Receptor Gene Polymorphisms with the Clinical Course of Wilson Disease 
JIMD Reports  2012;8:73-80.
Background: Dopamine receptor D2 (DRD2) polymorphisms are proposed to be important factors in the presentation of neuropsychiatric symptoms in many disorders, including decreased striatum levels of dopamine D2 receptors in Wilson disease. The present study investigated the association between DRD2 gene polymorphisms and clinical manifestation of Wilson disease.
Methods: Analyzing data from 97 symptomatic Wilson disease patients, we investigated the DRD2 gene polymorphisms rs1800497, rs1799732, and rs12364283. We assessed the polymorphisms impact on the phenotypic presentation of the disease.
Results: Generally, the DRD2 gene polymorphisms had no impact on the hepatic or neuropsychiatric clinical presentation of Wilson disease. However, rs1799732 deletion allele carriers with neuropsychiatric symptoms had earlier onset of WD symptoms by almost 6 years compared with individuals without this allele (22.5 vs. 28.3 years; P < 0.05). This unfavorable effect of the rs1799732 polymorphism was even more pronounced among adenosine triphosphatase 7B gene (ATP7B) p.H1069Q homozygous patients, in whom carriership of the deletion allele was related to earlier initial neuropsychiatric manifestation by 14 years (18.4 vs. 32.2 years; P < 0.01).
Conclusions: Genetic variation of DRD2, specifically the rs1799732 polymorphism, may produce an earlier clinical presentation of Wilson disease neuropsychiatric symptoms and signs that occur in the course of dopaminergic system impairment due to copper accumulation in the brain. We speculate that this effect may be due to the impact of DRD2 polymorphism on dopamine D2 receptor density, but further studies are needed to understand the mechanisms of such phenotypic effects.
PMCID: PMC3565646  PMID: 23430523
20.  Clinical and pharmacogenetic determinants for the discontinuation of non-ergoline dopamine agonists in Parkinson’s disease 
To identify determinants for the discontinuation of non-ergoline dopamine agonist (DA) treatment in patients with Parkinson’s disease (PD) and to identify genetic determinants in genes encoding dopamine receptor (DR)D2 and DRD3 in a exploratory analysis.
Patients included were first-time users of the non-ergoline DA ropinirole or pramipexole who had been diagnosed with PD before 2005. Treatment discontinuation was defined as a gap of 180 days or more between two refills of the DA. Non-genetic determinants for discontinuation were studied in the overall population, and genetic determinants [DRD2 141C Ins/Del, DRD2 (CA)n STR, DRD2 TaqIA, DRD3 MscI single nucleotide polymorphism (SNP) and DRD3 MspI SNP] were studied in a subgroup. Cox proportional hazard analysis was used to estimate the hazard ratios (HR) for the discontinuation of non-ergoline DA treatment.
The study population comprised 90 patients. Apomorphine use was associated with non-ergoline DA discontinuation, although the apomorphine group consisted only of three patients [HR 6.26; 95% confidence interval (CI) 1.85–21.2]. Daily levodopa dosages between 500 and 1000 mg were positively associated with discontinuation (HR 2.31; 95% CI 1.08–4.93). Included in the exploratory pharmacogenetic analysis were 38 patients. The absence of a 15× DRD2 CA repeat allele was significantly related with a decreased discontinuation of non-ergoline treatment (HR 0.23; 95% CI 0.07–0.81). The DRD3 MspI polymorphism showed a non-significant allele dose effect, suggestive of a causal relationship.
This study identified apomorphine use and levodopa dosages between 500 and 1000 mg as non-genetic and the 15× DRD2 CA repeat allele as genetic determinants for the discontinuation of non-ergoline DA treatment in patients with PD. More research is needed to replicate these findings.
PMCID: PMC2778789  PMID: 19669131
Determinants; Discontinuation; Dopamine agonists; Dopamine receptors; Parkinson’s disease; Pharmacogenetics; Pramipexole; Ropinirole
21.  Generational Association Studies of Dopaminergic Genes in Reward Deficiency Syndrome (RDS) Subjects: Selecting Appropriate Phenotypes for Reward Dependence Behaviors 
Abnormal behaviors involving dopaminergic gene polymorphisms often reflect an insufficiency of usual feelings of satisfaction, or Reward Deficiency Syndrome (RDS). RDS results from a dysfunction in the “brain reward cascade,” a complex interaction among neurotransmitters (primarily dopaminergic and opioidergic). Individuals with a family history of alcoholism or other addictions may be born with a deficiency in the ability to produce or use these neurotransmitters. Exposure to prolonged periods of stress and alcohol or other substances also can lead to a corruption of the brain reward cascade function. We evaluated the potential association of four variants of dopaminergic candidate genes in RDS (dopamine D1 receptor gene [DRD1]; dopamine D2 receptor gene [DRD2]; dopamine transporter gene [DAT1]; dopamine beta-hydroxylase gene [DBH]). Methodology: We genotyped an experimental group of 55 subjects derived from up to five generations of two independent multiple-affected families compared to rigorously screened control subjects (e.g., N = 30 super controls for DRD2 gene polymorphisms). Data related to RDS behaviors were collected on these subjects plus 13 deceased family members. Results: Among the genotyped family members, the DRD2 Taq1 and the DAT1 10/10 alleles were significantly (at least p < 0.015) more often found in the RDS families vs. controls. The TaqA1 allele occurred in 100% of Family A individuals (N = 32) and 47.8% of Family B subjects (11 of 23). No significant differences were found between the experimental and control positive rates for the other variants. Conclusions: Although our sample size was limited, and linkage analysis is necessary, the results support the putative role of dopaminergic polymorphisms in RDS behaviors. This study shows the importance of a nonspecific RDS phenotype and informs an understanding of how evaluating single subset behaviors of RDS may lead to spurious results. Utilization of a nonspecific “reward” phenotype may be a paradigm shift in future association and linkage studies involving dopaminergic polymorphisms and other neurotransmitter gene candidates.
PMCID: PMC3290972  PMID: 22408582
dopamine; gene polymorphisms; generational association studies; phenotype; “super normal” controls; Reward Deficiency Syndrome (RDS)
22.  No Evidence for Strong Recent Positive Selection Favoring the 7 Repeat Allele of VNTR in the DRD4 Gene 
PLoS ONE  2011;6(8):e24410.
The human dopamine receptor D4 (DRD4) gene contains a 48-bp variable number of tandem repeat (VNTR) in exon 3, encoding the third intracellular loop of this dopamine receptor. The DRD4 7R allele, which seems to have a single origin, is commonly observed in various human populations and the nucleotide diversity of the DRD4 7R haplotype at the DRD4 locus is reduced compared to the most common DRD4 4R haplotype. Based on these observations, previous studies have hypothesized that positive selection has acted on the DRD4 7R allele. However, the degrees of linkage disequilibrium (LD) of the DRD4 7R allele with single nucleotide polymorphisms (SNPs) outside the DRD4 locus have not been evaluated. In this study, to re-examine the possibility of recent positive selection favoring the DRD4 7R allele, we genotyped HapMap subjects for DRD4 VNTR, and conducted several neutrality tests including long range haplotype test and iHS test based on the extended haplotype homozygosity. Our results indicated that LD of the DRD4 7R allele was not extended compared to SNP alleles with the similar frequency. Thus, we conclude that the DRD4 7R allele has not been subjected to strong recent positive selection.
PMCID: PMC3164202  PMID: 21909391
23.  Two-stage case-control association study of dopamine-related genes and migraine 
BMC Medical Genetics  2009;10:95.
We previously reported risk haplotypes for two genes related with serotonin and dopamine metabolism: MAOA in migraine without aura and DDC in migraine with aura. Herein we investigate the contribution to migraine susceptibility of eight additional genes involved in dopamine neurotransmission.
We performed a two-stage case-control association study of 50 tag single nucleotide polymorphisms (SNPs), selected according to genetic coverage parameters. The first analysis consisted of 263 patients and 274 controls and the replication study was composed by 259 cases and 287 controls. All cases were diagnosed according to ICHD-II criteria, were Spanish Caucasian, and were sex-matched with control subjects.
Single-marker analysis of the first population identified nominal associations of five genes with migraine. After applying a false discovery rate correction of 10%, the differences remained significant only for DRD2 (rs2283265) and TH (rs2070762). Multiple-marker analysis identified a five-marker T-C-G-C-G (rs12363125-rs2283265-rs2242592-rs1554929-rs2234689) risk haplotype in DRD2 and a two-marker A-C (rs6356-rs2070762) risk haplotype in TH that remained significant after correction by permutations. These results, however, were not replicated in the second independent cohort.
The present study does not support the involvement of the DRD1, DRD2, DRD3, DRD5, DBH, COMT, SLC6A3 and TH genes in the genetic predisposition to migraine in the Spanish population.
PMCID: PMC2758864  PMID: 19772578
24.  Dopamine Receptor Mediation of the Exploratory/Hyperactivity Effects of Modafinil 
Neuropsychopharmacology  2011;36(7):1385-1396.
Modafinil (2-((diphenylmethyl)sulfinyl)acetamide) is described as an atypical stimulant and is a putative cognition enhancer for schizophrenia, but the precise mechanisms of action remain unclear. Receptor knockout (KO) mice offer an opportunity to identify receptors that contribute to a drug-induced effect. Here we examined the effects of modafinil on exploration in C57BL/6J mice, in dopamine drd1, drd2, drd3, and drd4 wild-type (WT), heterozygous (HT), and KO mice, and in 129/SJ mice pretreated with the drd1 antagonist SCH23390 using a cross-species test paradigm based on the behavioral pattern monitor. Modafinil increased activity, specific exploration (rearing), and the smoothness of locomotor paths (reduced spatial d) in C57BL/6J and 129/SJ mice (increased holepoking was also observed in these mice). These behavioral profiles are similar to that produced by the dopamine transporter inhibitor GBR12909. Modafinil was ineffective at increasing activity in male drd1 KOs, rearing in female drd1 KOs, or reducing spatial d in all drd1 KOs, but produced similar effects in drd1 WT and HT mice as in C57BL/6J mice. Neither dopamine drd2 nor drd3 mutants attenuated modafinil-induced effects. Drd4 mutants exhibited a genotype dose-dependent attenuation of modafinil-induced increases in specific exploration. Furthermore, the drd1 KO effects were largely supported by the SCH23390 study. Thus, the dopamine drd1 receptor appears to exert a primary role in modafinil-induced effects on spontaneous exploration, whereas the dopamine drd4 receptor appears to be important for specific exploration. The modafinil-induced alterations in exploratory behavior may reflect increased synaptic dopamine and secondary actions mediated by dopamine drd1 and drd4 receptors.
PMCID: PMC3096808  PMID: 21412225
modafinil; dopamine receptors; D1; D4; exploration; dopamine transporter; D1; D2; D3; D4; dopamine; exploration; knockout; mice; modafinil; neurotransmitters; psychostimulants; receptor pharmacology
25.  Role of Nicotine Dependence in the Association between the Dopamine Receptor Gene DRD3 and Major Depressive Disorder 
PLoS ONE  2014;9(6):e98199.
The aims of this study were to analyze associations of dopamine receptor genes (DRD1-5) with Major Depressive Disorder (MDD) and nicotine dependence (ND), and to investigate whether ND moderates genetic influences on MDD.
The sample was ascertained from the Finnish Twin Cohort. Twin pairs concordant for smoking history were recruited along with their family members, as part of the multisite Nicotine Addiction Genetics consortium. Genetic association analyses were based on 1428 adults. Total of 70 tagging single nucleotide polymorphisms within the dopamine receptor genes were genotyped and analyzed for association with MDD, ND, and MD-ND co-morbidity. Individual level logistic regression analyses were based on 1296 adults with data on ND and MDD diagnoses, as well as on dopamine receptor genotypes adjusted for sex, age, and alcohol use. Four independent samples, such as population-based and case-control samples, were used for replication.
Rs2399496, located 1.5 kb downstream of DRD3, showed suggestive association for MDD (p = 0.00076) and significant association for MDD-ND co-morbidity (p = 0.000079). Suggestive gene-(rs2399496) by-ND-interaction justified analyses by genetic risk variant and ND status. Individuals with ND and two minor alleles (AA) of rs2399496 had almost six-fold risk for MDD (OR 5.74, 95%CI 3.12–10.5, p = 9.010e-09) compared to individuals without ND and with two major alleles (TT).
Significant association between a variant downstream of DRD3 and a co-morbid MDD-ND phenotype was detected. Our results further suggest that nicotine dependence may potentiate the influence of the DRD3 genetic variant on MDD.
PMCID: PMC4057087  PMID: 24927283

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