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PubMed1999

DNA methylation at the putative promoter region of the human dopamine D2 receptor gene.

DNA methylation was investigated in the putative promoter region of the human dopamine D2 receptor gene (DRD2). Twenty-two DNA samples from two types of cells differentially expressing D2 receptors, striatum and lymphocytes, were subjected to bisulphite modification-based mapping of methylated cytosines. In the tested region, the DNA from lymphocytes exhibited a significantly higher degree of methylation than that from striata. In addition, a significantly higher proportion of methylated to unmethylated cytosines was detected in DRD2 from the right than the left striatum, and a trend towards a greater degree of methylation was detected in older than in younger individuals. These DRD2 methylation findings are consistent with dopamine D2 receptor binding data from the literature which support the idea that DNA methylation plays a role in regulation of DRD2 expression.

Adult↗
PubMed2003

Impulsiveness as the intermediate link between the dopamine receptor D2 gene and alcohol dependence.

OBJECTIVES: Reinforcement and reward processes have been proposed as being an intermediate link between the risk for alcohol dependence and the gene coding for the dopamine receptor D2 (DRD2). This hypothesis remains open to speculation, and personality traits such as impulsiveness, a core dimension in addictive disorders, should also be taken into account. For instance, recent evidence in rats showed that DRD2 antagonists might increase impulsivity in decreasing the value of delayed rewards. METHODS: Considering the pro-impulsiveness role of ethanol observed in clinical practice and epidemiological studies, we analysed the Barratt impulsiveness scores in a sample of 92 alcohol-dependent French patients (57 men and 35 women), according to the TaqI A polymorphism of the DRD2 gene. RESULTS: A2/A2 and A1/A2 genotypes were significantly associated with a higher global impulsiveness than A1/A1 genotype (P=0.02 and P=0.03, respectively). CONCLUSIONS: We propose that reward-related impulsiveness may constitute a risk factor for alcohol dependence, and that this core temperament could be partly mediated by the DRD2 gene.

Alcoholism↗
PubMed2006

No association of dopamine receptor sensitivity in vivo with genetic predisposition for alcoholism and DRD2/DRD3 gene polymorphisms in alcohol dependence.

This study sought to examine dopamine receptor sensitivity among alcoholics in vivo and to explore whether this sensitivity might be associated with functional variations of dopamine D2 (DRD2) and D3 (DRD3) receptor genes along with a genetic predisposition for alcoholism as reflected by an alcohol-dependent first-degree relative. We analyzed the -141C Ins/Del polymorphism in the promoter region of the DRD2 gene and the Ser9Gly (BalI) polymorphism in exon 1 of the DRD3 gene in 74 alcohol-dependent Caucasian men with or without genetic predisposition for alcoholism. In vivo dopamine receptor sensitivity was assessed by measuring apomorphine-induced growth hormone release. A three-way analysis of variance revealed no significant effects of DRD2, DRD3 genotypes and genetic predisposition on dopamine receptor sensitivity. Given the explorative and preliminary character of this investigation, we cannot provide evidence that in alcohol-dependent Caucasian men a genetic predisposition for alcoholism along with functional variants of the DRD2 and DRD3 genes are associated with differences in dopamine receptor sensitivity.

Adult↗
PubMed2004

Lack of interaction between a polymorphism in the dopamine D2 receptor gene and the clinical features of migraine.

The purpose of this study was to evaluate whether a particular genotype of the dopamine D2 receptor (DRD2) gene would affect the clinical features of migraine. In a group of 118 migraineurs (55 migraine with aura and 63 migraine without aura patients), we tested the association of the biallelic C/T NcoI DRD2 polymorphism with several characteristics of the disease. Genotype and allele frequencies resulted similarly distributed in migraine with aura and migraine without aura patients (chi2 = 1.58, P = 0.45 and chi2 = 0.09, P = 0.77, respectively). The different DRD2 genotypes (C/C, C/T and T/T) had no significant effects on age at onset of migraine, presence of premonitory phenomena, frequency of headache attacks, associated symptoms, psychological features and quality of life of our migraine patients. The results of our study do not support a role for the DRD2 gene in modifying the clinical features of migraine.

Adult↗
PubMed2000

Genetic polymorphism of dopamine D2 receptors in Parkinson's disease and interactions with cigarette smoking and MAO-B intron 13 polymorphism.

Genetic polymorphisms of dopamine D2 receptors (DRD2) may be susceptibility factors for Parkinson's disease due to their influence on dopamine response and association with cigarette smoking, which is inversely related to risk of Parkinson's disease. Relations of TaqIA and TaqIB DRD2 genotypes with Parkinson's disease were investigated and tested for interactive effects with smoking and the monoamine oxidase B (MAO-B) intron 13 polymorphism previously found to be related to smoking. Study subjects were 152 cases of idiopathic Parkinson's disease and 231 controls. The smoking history of all genotyped subjects was known. Subjects of genotype B12 were more frequent among cases than controls (27% and 23.8%, respectively), and were more frequent among "ever smokers" than "never smokers", among controls (27.8% and 17.2%, respectively), although these associations were not statistically significant. Neither TaqIA or TaqIB genotypes modified the inverse relation of smoking and Parkinson's disease. When genotypes for DRD2 were considered in combination with genotypes for intron 13 of MAO-B, genotype combinations with high risk of Parkinson's disease were found; although the MAO-B/DRD2 interaction did not reach statistical significance after Bonferroni correction for multiple comparisons, these results are suggestive of a possible synergism between MAOB and DRD2 genes with respect to Parkinson's disease.

Adult↗
PubMed1996

A genetic linkage study of the D2 dopamine receptor locus in heavy drinking and alcoholism.

BACKGROUND: Reports of an association between restriction fragment length polymorphisms (RFLPs) at the dopamine D2 receptor (DRD2) locus and alcoholism have suggested involvement of that locus in the aetiology of alcoholism. METHOD: Sib pair linkage analyses were conducted in families multiply affected by alcoholism, using both the Taql 'A' RFLP and a microsatellite repeat polymorphism at the DRD2 locus. RESULTS: The 'Identical By Descent' analysis provided significant evidence of an effect of the DRD2 locus on the liability to develop heavy drinking (P < 0.0016) and Research Diagnostic Criteria alcoholism (P < 0.0003) in the first sample of families studied. However, this result was explicable by the segregation of alleles in a single large sibship, and it was not replicated in a second sample of families. CONCLUSIONS: The results do not support linkage between the DRD2 locus and alcoholism in most of the families studied. It remains possible that this locus influences the predisposition to alcoholism in some families.

Alcoholism↗
PubMed1998

Association between dopamine receptor genes and migraine without aura in a Sardinian sample.

BACKGROUND: Migraine seems to be caused by a combination of environmental and genetic factors. Clinical and pharmacologic evidence supports the hypothesis that dopaminergic transmission is involved in the pathogenesis of migraine. OBJECTIVE: The current report concerns a genetic study to test the involvement of genes for dopamine (DA) receptors D2 (DRD2), D3 (DRD3), and D4 (DRD4) in migraine without aura, particularly in a subgroup with enhanced DA sensitivity. METHODS: For the first time, a family-based association method--the Transmission Disequilibrium Test (TDT)--was used to examine an isolated population, such as Sardinians. We studied 50 nuclear families of patients affected by migraine without aura. The subgroup of dopaminergic migraineurs was selected based on the presence of both nausea and yawning immediately before or during the pain phase of migraine. RESULTS: No association was detected using the TDT between DRD3, DRD4, and migraine without aura either in the overall sample or in the subgroup. No difference was observed in DRD2 allelic distribution in the overall sample, although the allelic distribution at the DRD2 locus differed significantly in the subgroup of dopaminergic migraineurs (p = 0.004). Allele 1 of the TG dinucleotide intronic noncoding polymorphism of the DRD2 locus was the individual allele that appeared to be in disequilibrium with migraine without aura (p = 0.02). CONCLUSIONS: Our data suggest that a genetic approach could be useful in providing molecular support to the hypothesis that hypersensitivity of the dopaminergic system may represent the pathophysiologic basis of migraine, at least in a subgroup of patients.

Adolescent↗
PubMed2000

Evaluation of the role of the D2 dopamine receptor in myoclonus dystonia.

A novel Val154-->Ile mutation in the D2 dopamine receptor (DRD2) on chromosome 11q23 has recently been shown to be associated with myoclonus dystonia (M-D) in one large family. Sequence analysis of the DRD2 gene in 5 M-D patients from different families did not reveal any mutations, nor was there evidence of linkage to the 11q23 region in the DRD2 gene in four other families. Receptor binding and signal transduction assays of the DRD2 mutant and wild-type receptors revealed identical agonist and antagonist affinities and functional responses. These studies suggest that M-D is genetically heterogeneous. The molecular mechanisms through which the Val-->Ile mutation may contribute to M-D remain to be determined.

Adolescent↗
PubMed2000

[The study of polymorphism of dopamine D2 receptor gene in men from different ethnic groups with acute alcoholic psychosis].

The polymerase chain reaction of DNA synthesis was used to analyze the polymorphism of TaqI A and NcoI loci of dopamine D2 receptor gene (DRD2) in 170 Tatar and Russian males with acute alcoholic psychosis. No differences were found in the distribution of frequencies of genotypes and alleles of DRD2 gene between the populations. There were differences in the distribution of the frequencies of genotypes of the locus TaqI A and haplotypes of the gene DRD2 were revealed between patients and controls of the same nationality; moreover these differences were significant in the Russians. The findings suggest that alcoholics show a selection aimed at eliminating individuals with haplotypes who carry Al and N2 alleles and who are homozygous by one of these alleles. This may account for a decrease in the frequency of locus TaqI A genotypes carrying A1 allele, primarily A1/A1 homozygotes and for the loss of haplotypes of TaqI A and NcoI loci of the gene DRD2 -A1N1N2, A1A2N2 in men with acute alcoholic psychosis as compared with the controls.

Acute Disease↗
PubMed2003

The Taq IA and Ser311 Cys polymorphisms in the dopamine D2 receptor gene and obesity.

Dopamine D2 receptors (DRD2) in the central nervous system are involved in the regulation of feeding. It remains to be elucidated if mutations in the DRD2 gene contribute to the development of obesity. The aim of the present study was to investigate whether the Taq IA and Ser311Cys polymorphisms in the DRD2 gene are associated with obesity in Nauruan and Australian subjects. Subjects were selected based on extremes of the body mass index (BMI) distribution. Two groups of Australian women were selected. The leanest group had a mean BMI of 22.5 kg/m2 (range: 20.3-24.3) and the heaviest group had a mean of 36.1 kg/m2 (32.5-44.1). Four groups of Nauruan subjects were selected. Leanest men had a mean BMI of 33.0 kg/m2 (28.4-36.9), heaviest men had a mean of 52.8 kg/m2 (46.5-69.2), leanest women had a mean of 34.8 kg/m2 (28.2-41.8) and heaviest women had a mean of 55.1 kg/m2 (49.3-73.8). Subjects were genotyped for the Taq IA and Ser311Cys polymorphisms using polymerase chain reaction (PCR) restriction fragment length polymorphism analysis and allelic discrimination Taqman PCR respectively. Leanest and heaviest groups were examined for differences in genotype frequency. Taq IA and Ser311Cys genotype frequencies did not differ significantly between leanest and heaviest Nauruan groups, or between leanest and heaviest Australians. Haplotype frequencies of these polymorphisms did not differ between leanest and heaviest groups. The Taq IA and Ser311Cys polymorphisms in the DRD2 gene are unlikely to be common causes of obesity in these populations.

Adult↗
PubMed1993

Recent developments in alcoholism:molecular biology and behavior.

Following our initial observation that the A1 allele of the D2 dopamine receptor (DRD2) gene was associated with alcoholism, a number of studies, both in the United States and abroad, have attempted to replicate and extend this finding in different Caucasian populations. In nine independent studies containing a total of 491 heterogeneous alcoholics (less severe and severe) and 495 heterogeneous controls (assessed and unassessed for alcoholism), the prevalence of the A1 allele was 43.0% in the former group compared with 25.7% in the latter groups (odds ratio = 2.18, p < 10(-6). The prevalence of the A1 allele increased to 56.3% in a more homogeneous sample of 158 severe alcoholics (odds ratio = 3.32, p < 10(-8)). Moreover, the B1 allele of the DRD2 gene was also found to be significantly associated with severe alcoholism. Additional data are accruing which also implicate the DRD2 A1 and B1 alleles in substance use disorders other than alcoholism. If further studies continue to support the results currently available, they would indicate that the DRD2 gene is the most prominent single gene determinant of susceptibility to severe substance abuse. However, the larger role still appears to be played by a combination of environmental factors and as yet unidentified genes.

Alcoholism↗
PubMed1994

Polymorphisms of the D2 dopamine receptor gene and alcoholism and other substance use disorders.

The A1 (minor) allele of the D2 dopamine receptor (DRD2) gene has been shown to be associated with alcoholism, particularly the severe form of this disorder. This allele has also been found to be involved in a variety of other substance use disorders including, cocaine and nicotine dependence, polysubstance abuse and obesity. Moreover, reduced dopaminergic function has been found in subjects carrying the DRD2 A1 allele, suggesting that the DRD2 may be a reinforcement or reward gene. Analysis of the available data suggests that the DRD2 variants represent one of the most prominent single-gene determinants of susceptibility to severe alcoholism and other substance use disorders. However, environmental factors and other genes must, in combination, play the larger role.

Alcoholism↗
PubMed1997

Dopamine D2 receptor gene and alcoholism among four aboriginal groups and Han in Taiwan.

Previous studies examining the putative association between DRD2 TaqI A1 and alcoholism have produced conflicting results. Major critiques of such studies include potential confounding arising from population admixture by inappropriate selection of controls, failure to screen out substance abusers from controls, and the failure to assess the severity of alcoholics. To address these issues, we compared the allelic frequency of two polymorphisms of DRD2, TaqI A and NcoI, among severe alcoholics and their ethnically matched nonalcoholic controls within four major aboriginal groups and Han (Chinese) in Taiwan. The sample of alcoholics and controls examined for the five groups included 36 and 31 (Atayal), 24 and 23 (Ami), 58 and 58 (Bunun), 35 and 35 (Paiwan), and 50 and 66 (Han). A borderline association between TaqI A1 and alcoholism among the Ami (P = 0.08) and an association between NcoI N1 and alcoholism among Han (P = 0.01) were found. Results of haplotype analysis further confirm that the frequency of haplotype A1N1 was higher in alcoholics than in controls for the Ami (P = 0.01) and Han (P = 0.03). If controls with tobacco abuse were excluded from the analysis, the results remained unchanged. Severity in medical complications of alcohol dependence with withdrawal symptoms was not associated with higher prevalence of DRD2 TaqI A1 or NcoI N1 alleles. The absence of an association between DRD2 and alcoholism among the three aboriginal groups suggests either a higher rate of phenocopies among aboriginal alcoholics or genetic heterogeneity in the susceptibility to alcoholism.

Alcoholism↗
PubMed1998

No association of a functional polymorphism in the dopamine D2 receptor promoter region with bipolar or unipolar affective disorders.

The dopaminergic system, along with the serotonergic and noradrenergic systems, has been implicated in the etiology of mood disorders. An association study of a functional variant in the promoter region of the dopamine D2 receptor (DRD2) with bipolar affective disorder I or unipolar major affective disorders was performed. Variable expression of the DRD2 gene in vitro has been shown with this promoter polymorphism. One hundred and thirty-one unrelated bipolar patients, 128 unrelated unipolar patients, and 262 controls were used in the study. There were no significant differences in DRD2 allele or genotype frequencies between the affective disorder and control groups. These results do not support a major role for the DRD2 gene in the etiology of either bipolar or unipolar affective disorders.

Bipolar Disorder↗
PubMed2005

Sex differences in clinical and genetic determinants of levodopa peak-dose dyskinesias in Parkinson disease: an exploratory study.

BACKGROUND: Several factors, both clinical and genetic, may account for the risk of developing levodopa-induced peak-dose dyskinesias (PDD) in patients with Parkinson disease, but it is unclear how these factors interact for modulating the individual susceptibility for PDD. OBJECTIVE: To examine clinical and genetic risk factors for determining individual susceptibility of PDD in patients with Parkinson disease. DESIGN: Cohort study. SETTING: Referral center for Parkinson disease in Calabria, southern Italy. Patients Two hundred fifty patients with Parkinson disease were screened for the presence or absence of PDD following a short-term levodopa administration, and 215 subjects were available for further evaluations, including genotypic analysis of the CA dinucleotide short tandem repeat (CAn-STR) polymorphism located in the dopamine receptor D2 gene (DRD2). RESULTS: One hundred five patients (48.8%) exhibited PDD following short-term levodopa administration, and 110 patients (51.2%) did not. Multivariate logistic regression analysis showed that independent predictors for the occurrence of PDD were female sex, earlier age at onset of Parkinson disease, longer duration of treatment, and higher dose of levodopa. Genetic factors related to the DRD2 CAn-STR polymorphism were not independent predictors for PDD in the total population, but they had a strong protective effect on the appearance of PDD when the multivariate analysis was performed in men (odds ratio, 0.34 [95% confidence interval, 0.14-0.84]). In women, a genetic protective effect on PDD was not evident. CONCLUSIONS: Risk factors for PDD, both clinical and genetic, act in different ways for men and women. Genetic factors related to the DRD2 polymorphic status have a protective effect on PDD development in men but not in women. A female sex-related effect for the risk of PDD may be so strong that it overcomes any protective effect due to genetic factors.

Age of Onset↗
PubMed2004

Association of specific haplotypes of D2 dopamine receptor gene with vulnerability to heroin dependence in 2 distinct populations.

CONTEXT: Dopamine receptor-mediated pathways play critical roles in the mechanism of addiction. However, associations of the D(2) dopamine receptor gene (DRD2) with substance abuse are controversial. OBJECTIVE: To determine whether susceptibility sites resided at DRD2. DESIGN: Haplotype-based case-control analysis of 2 distinct populations using 10 single nucleotide polymorphisms (SNPs) with heroin dependence. SETTING: Universities of Mainz and Bonn, Germany, and 3 local hospitals in southwestern China. Patients Cases and control subjects recruited from China (486 cases, 313 controls) and Germany (471 cases, 192 controls). INTERVENTIONS: Genotyping for 10 SNPs by 5'-exonuclease fluorescence assays. The D' value of linkage disequilibrium and haplotypes were generated by the expectation-maximization algorithm. MAIN OUTCOME MEASURES: Genotype, allele, and haplotype frequencies were compared between cases and controls by chi(2) tests constructed for each population. An additional 32 SNPs randomly distributed in the genome were genotyped for detecting population admixture in the 2 populations. RESULTS: A haplotype block of 25.8 kilobases (kb) was defined by 8 SNPs extending from SNP3 (TaqIB) at the 5' end to SNP10 site (TaqIA) located 10 kb distal to the 3' end of the gene. Within this block, specific haplotype cluster A (carrying TaqIB1 allele) was associated with a high risk of heroin dependence in Chinese patients (P = 1.425 x 10(-22); odds ratio, 52.80; 95% confidence interval, 7.290-382.5 for 8-SNP analysis). A putative recombination "hot spot" was found near SNP6 (intron 6 ins/del G), creating 2 new daughter haplotypes that were associated with a lower risk of heroin dependence in Germans (P = 1.94 x 10(-11) for 8-SNP analysis). There was no evidence of population stratification in either population. CONCLUSIONS: These results strongly support a role of DRD2 as a susceptibility gene with heroin dependence in Chinese patients and was associated with low risk of heroin dependence in Germans.

Adult↗
PubMed1997

Association between early-onset alcoholism and the dopamine D2 receptor gene.

We examined the allelic association between the dopamine D2 receptor (DRD2) gene and alcoholism in 100 biologically unrelated Japanese alcoholics and 93 unrelated controls. Genomic DNA was prepared from peripheral white blood cells using the phenol-chloroform method. A 310-bp region surrounding the TaqA site at the DRD2 locus was amplified by polymerase chain reaction (PCR), and the PCR product was incubated with TaqI. The A1 allele remained intact while the A2 allele was cut. The frequency of the A1/A1 genotype and the frequency of the A1 allele were higher in early-onset alcoholics than in controls, P < 0.05 and P < 0.01, respectively. Moreover, the frequency of the A1/A1 genotype and the frequency of the A1 allele were higher in early-onset alcoholics with family histories of alcohol dependence than in controls, P < 0.01 and P < 0.01, respectively. The results indicate that the DRD2 gene is associated with susceptibility to early-onset alcoholism, and that each additional A1 allele shifts onset of alcoholism to an earlier age.

Adult↗
PubMed1997

No association between polymorphisms in the human dopamine D3 and D4 receptors genes and alcoholism.

The human dopamine D2 receptor gene (DRD2) has received considerable attention for the past several years as a potential candidate that may affect susceptibility to alcoholism. The association studies that compared the frequencies of alleles of DRD2 gene between alcoholics and control groups have produced equivocal results. Dopamine D3 and D4 receptor genes (DRD3 and DRD4) are in the same class as DRD2 but with different pharmacological properties. We have used relative risk and haplotype relative risk approaches to test associations between alleles of DRD3 and DRD4 genes and alcoholism. For relative risk studies 162 probands from multiple incidence alcoholic families have been compared to 89 psychiatrically normal controls. Haplotype relative risk approaches have used 29 alcoholic probands in which both parents were available for genotyping. The Bal I restriction enzyme site in DRD3 and tandem repeat (VNTR) in DRD4 genes polymorphisms were used to genotype the above samples. The results of relative risk approaches for both DRD3 and DRD4 genes were negative for comparisons of alcoholics and subtypes of alcoholics with normal controls. Haplotype relative risk approaches also were negative for both genes. These results suggest that any role played by these receptors may account for only part of the variation in susceptibility to alcoholism.

Alcoholism↗