A functional polymorphism in the promoter region of the dopamine D2 receptor gene is associated with schizophrenia

Pharmacogenetics of dopamine receptors and response to antipsychotic drugs in schizophrenia – an update

A considerable number of pharmacogenetic studies have been performed in recent years to define the association of antipsychotic medication response with dopamine receptor polymorphisms and, despite contradictory results, decisive trends have emerged. For the dopamine D2 receptor (DRD2), a trend toward an association with favorable response seems to emerge for the -141C Ins allele of the DRD2 -141C Ins/Del polymorphism and the A1 allele of the Taq1A polymorphism. In the case of the D3 receptor, the Ser9Gly polymorphism has been extensively investigated and a pattern of association is seen between the Ser9 allele and a response to typical antipsychotics, and between the Gly9 allele and a response to atypical antipsychotics. For the D4 receptor, no convincing association results have been reported to date. These trends are discussed with regard to methodological directives and functional implications.

DRD2 -141C insertion/deletion polymorphism is not associated with schizophrenia: results of a meta-analysis

The gene DRD2, which codes for dopamine receptor D2, has been considered a prime candidate for allelic association testing with schizophrenia based on the strong evidence for involvement of this protein in disease pathophysiology. Recent meta-analyses confirmed a small but reliable association between schizophrenia and the cysteine-coding allele of the Cys311Ser polymorphism of DRD2. In the present study, we sought to determine if another polymorphism (the -141C insertion/deletion) in the same gene, which has been reported to be associated with schizophrenia in several individual studies, would show a similar pattern of association with the disease in a pooled dataset. The pooled odds ratio for the insertion allele obtained from 10 case-control studies was 1.1, which was not significant (P = 0.580); however, there was marked heterogeneity among the findings of individual studies, suggesting that some underlying factor influenced the size of their observed effects. Yet, neither ethnicity, the age of the control group, nor the gender composition of the samples reliably influenced effect size. Because linkage disequilibrium patterns between various DRD2 polymorphisms are not yet known, it remains possible that divergent meta-analytic findings at both commonly examined mutation sites within DRD2 are accurate. Haplotype analysis within this gene would be useful for definitively specifying the role of this gene in the etiology of schizophrenia.

Association of dopaminergic and serotonergic genes with tardive dyskinesia in patients with chronic schizophrenia

Tardive dyskinesia (TD) is a long-term adverse effect of antipsychotic drugs that are dopamine D2 receptor blockers. Serotonin receptor antagonism has been proposed as a common mechanism contributing to the low extrapyramidal side effect profile of atypical antipsychotic drugs. We evaluated candidate dopamine and serotonin genes for association with drug-induced TD. We examined three polymorphisms in the dopamine D2 receptor gene (DRD2), two sites in the 3' region of the dopamine transporter (DAT) gene, two sites in the promoter and coding region of the dopamine D4 (DRD4) receptor gene, as well as polymorphic sites in the serotonin 6 receptor gene, the serotonin transporter gene and the tryptophan hydroxylase gene, for association with TD susceptibility. Schizophrenic patients with (n=59) and without TD (n=63), matched for antipsychotic drug exposure and other relevant variables, were studied. No significant associations were found. Within the limitations imposed by the size of the clinical sample, these findings suggest that the above polymorphic loci do not contribute significantly to risk for TD. Further examination of loci that yielded positive results at a trend level and investigation of other candidate genetic loci coding for antipsychotic drug targets is warranted.

Association in Japanese patients between neuroleptic malignant syndrome and functional polymorphisms of the dopamine D(2) receptor gene

A genetic predisposition to the development of neuroleptic malignant syndrome (NMS) has been suggested by clinical studies. Although the molecular basis of NMS is unclear, a dopaminergic blockade mechanism has been considered the main cause. We therefore investigated the association between NMS and three functional polymorphisms of the dopamine D(2) receptor (DRD(2)) gene: TaqI A, -141C Ins/Del, and Ser311Cys. Subjects included 32 Japanese patients, previously diagnosed with NMS, and 132 schizophrenic patients treated with neuroleptics without occurrence of NMS. Polymerase chain reaction and restriction fragment length polymorphism analyses were performed to determine each genotype. We found significant differences in genotypic and allelic frequencies of the -141C Ins/Del polymorphism between patients with and without NMS. The -141C Del allele was significantly more frequent in the NMS group (23.4 vs 11.7%, P=0.026). Similarly, the proportion of -141C Del allele carriers was significantly higher in the NMS group (40.6 vs 20.5%, P=0.022). No significant differences between the two groups were seen for allelic and genotypic frequencies of the TaqI A and Ser311Cys polymorphisms. This result suggests that the -141C Ins/Del polymorphism is likely to predispose toward the development of NMS, probably together with other unidentified factors.

The molecular genetics of schizophrenia: new findings promise new insights

The high heritability of schizophrenia has stimulated much work aimed at identifying susceptibility genes using positional genetics. However, difficulties in obtaining clear replicated linkages have led to the scepticism that such approaches would ever be successful. Fortunately, there are now signs of real progress. Several strong and well-established linkages have emerged. Three of the best-supported regions are 6p24-22, 1q21-22 and 13q32-34. In these cases, single studies achieved genome-wide significance at P<0.05 and suggestive positive findings have also been reported in other samples. The other promising regions include 8p21-22, 6q21-25, 22q11-12, 5q21-q33, 10p15-p11 and 1q42. The study of chromosomal abnormalities in schizophrenia has also added to the evidence for susceptibility loci at 22q11 and 1q42. Recently, evidence implicating individual genes within some of the linked regions has been reported and more importantly replicated. The weight of evidence now favours NRG1 and DTNBP1 as susceptibility loci, though work remains before we understand precisely how genetic variation at each locus confers susceptibility and protection. The evidence for catechol-O-methyl transferase, RGS4 and G72 is promising but not yet persuasive. While further replications remain the top priority, the respective contributions of each gene, relationships with aspects of the phenotype, the possibility of epistatic interactions between genes and functional interactions between the gene products will all need investigation. The ability of positional genetics to implicate novel genes and pathways will open up new vistas for neurobiological research, and all the signs are that it is now poised to deliver crucial insights into the nature of schizophrenia.

Polymorphisms of the dopamine D2 receptor, serotonin transporter, and GABA(A) receptor beta(3) subunit genes and alcoholism in Mexican-Americans

The etiology of alcohol dependence is a complex interaction of psychosocial and biologic factors. To study the impact of genetic factors that play an important role in an individual's vulnerability to alcohol abuse and dependence, we examined the genetic variations of the major neurotransmitter genes, including the dopamine D2 receptor (DRD2) TaqI A, B, and -141C insertion/deletion (Ins/Del) polymorphisms, the serotonin transporter-linked polymorphic region (5-HTTLPR), and the gamma-aminobutyric acid A (GABA(A)) receptor beta(3) subunit gene (GABRbeta3), for 130 Mexican-American alcoholic men and 251 nonalcoholic control subjects (105 men and 146 women). The genotype frequency for the DRD2 -141C Ins/Del allele was significantly different between alcoholic and control subjects (P=.007). The frequency of the 5-HTTLPR short (S) allele was significantly higher in alcoholic individuals (61.5%) than in nonalcoholic control subjects (52.8%; P=.021). When smokers were excluded from both control and alcoholic groups, the association between the DRD2 -141C Ins allele, as well as between the 5-HTTLPR S allele, and alcoholism became significant at both genotypic and allelic levels. No positive association was found between alcoholism and the DRD2 TaqI A or B, or the GABRbeta3, genotype. Our findings indicate that the DRD2 -141C Ins allele and the 5-HTTLPR S allele are genetic risk factors for alcoholism in Mexican-Americans, and that smoking modulates the association between genetic risk factors and alcoholism.

From genomics to proteomics: new directions in molecular neuropsychiatry

Neuropsychiatry, like many other biomedical sciences, has been revolutionized by the advances in genomic technologies over the years. The advent of PCR (polymerase chain reaction) and the sequencing of the human genome have provided invaluable insights into the molecular genetics of the various psychiatric disorders through the study of candidate genes and linkage analyses. However, biological phenotype is dictated by protein expression, which has been shown to stray from the genetic blueprint designated by the genome. Consequently, the field of proteomics has recently emerged as a powerful means of exploring protein structure, function, and expression patterns. The ability to study disease at the gene and protein levels presents a tremendous opportunity for neuropsychiatric research, particularly in terms of the potential for developing therapeutic agents for novel protein targets.

Dopamine receptor D2 -141C Insertion/Deletion polymorphism in a Finnish population with schizophrenia

We examined the occurrence of the -141C Ins/Del polymorphism in 93 Finnish patients with schizophrenia. In comparison with previous studies with Japanese and Caucasian populations, the incidence of this polymorphism was unexpectedly low. The findings suggest that the frequency of the -141C Ins/Del polymorphism is lower in Northern Europe compared to other Caucasian and Japanese populations.

Genetic polymorphisms in the expression and treatment of neuropsychiatric disorders

Recent advances in molecular genetics have greatly increased the understanding of the pathophysiology of certain neurobehavioral disorders and the core symptoms of these disorders. This paper reviews key concepts important in understanding the genetics of neuropsychiatric disorders, and gives an overview of several different types of genetic disorders, including trinucleotide repeat disorders, and functional polymorphisms of monoamine neurotransmitter systems.

Combination of dopamine D2 receptor gene polymorphisms as a possible predictor of treatment-resistance to dopamine antagonists in schizophrenic patients

Both the A1 allele carriers of TaqI A and Del allele noncarriers of -141C Ins/Del for dopamine D(2) receptor (DRD(2)) gene polymorphisms have been reported to have a lowered DRD(2) density. The present study aimed to examine whether the combinations of these two DRD(2) gene polymorphisms predict treatment response to antidopaminergic agents in schizophrenic patients. Subjects consisted of 49 acutely exacerbated schizophrenic inpatients treated with bromperidol (30 cases, mean dose+/-S.D.: 11.4+/-4.8 mg/day) or nemonapride (19 cases, 18 mg/day). Clinical symptoms were evaluated using Brief Psychiatric Rating Scale (BPRS) before and 3 weeks after the treatment. DRD(2) genotypes were determined using a polymerase chain reaction method. The A1 noncarriers with a Del allele showed poorer percentage improvement in anxiety-depression symptom after 3-week treatment (n=9, 7.3+/-42.9%) than A1 carriers without Del alleles (n=25, 62.4+/-38.0%) or A1 noncarriers without Del alleles (n=10, 65.4+/-29.2%). However, these preliminary results should be replicated in further research with a larger number of the subjects in each haplotype subgroup.

Genetic predisposition to neuroleptic malignant syndrome : implications for antipsychotic therapy

The pathogenetic mechanism of neuroleptic malignant syndrome (NMS), a potentially lethal adverse effect of antipsychotics, is not well understood. In addition to acquired risk factors, clinical observations suggest a number of genetic factors predisposing patients to NMS. Recent findings in pharmacogenetics indicate that the genetic polymorphisms for drug-metabolizing enzymes, drug transporters, and possibly drug-targeting molecules, are associated with the interindividual differences in drug responses concerning both efficacy and adverse reactions. Genetic association studies have sought to identify polymorphisms influencing susceptibility to NMS, especially with respect to the dopamine D(2) receptor, serotonin receptor, and cytochrome p450 2D6. While a few candidate polymorphisms were associated with NMS, a large controlled study is needed to attain statistical power. On the other hand, NMS might include heterogeneous conditions with common characteristic symptoms but different causative mechanisms. Further analysis of individuals with identified genetic mutations or polymorphisms should advance our understanding of mechanisms underlying NMS.

Association and linkage disequilibrium between a functional polymorphism of the dopamine-2 receptor gene and schizophrenia in a genetically homogeneous Portuguese population

A functional polymorphism in the promoter region of the DRD2 gene has been found to be associated with schizophrenia in Japanese(1,2) and Swedish populations.(3) We attempted to replicate these findings in a genetically homogeneous Portuguese population using a family-based study design. Analysis of 78 trios revealed evidence for association between the -141 C Ins allele and schizophrenia using the haplotype relative risk (HRR) method (chi(2) = 9.30, P = 0.0023). Further examination of this sample using an alternative family-based association analysis method, the transmission disequilibrium test (TDT), of 33 informative matings from the Portuguese trios provided evidence for an allelic association and linkage disequilibrium between the insertion allele and schizophrenia (chi(2) = 8.76, P = 0.0031). These consistent results using two alternative family-based association analysis methods replicate the findings of previous reports, and thus further implicate a potential role for the dopamine-2 receptor in the genetic etiology of schizophrenia.

Pharmacogenetics of schizophrenia

Patients display significant differences in response to therapeutic agents which may be caused by a variety of factors. Among them, genetic components presumably play a major role. Pharmacogenetics is the field of research that attempts to unravel the relationship between genetic variation affecting drug metabolism (pharmacokinetic level) or drug targets (pharmacodynamic level) and interindividual differences in pharmacoresponse. In schizophrenia, pharmacokinetic studies have shown the role of genetic variants of the cytochrome P450 enzymes CYP2D6, CYP2C19, and CYP2C9 in the metabolism of neuroleptic drugs. At the level of the drug target, variants of the dopamine D3 and D4, and 5-HT2A and 5-HT2C receptors have been examined. A general problem of pharmacogenetic studies in schizophrenia is the high number of controversial findings which may be related to the lack of standardized phenotype definition. Recently, guidelines for an exact and comparable phenotype characterization have been proposed and will aid in designing and evaluating pharmacogenetic studies in the future. The final goal of pharmacogenetic studies-making a prediction of drug response at the level of the individual patient-will require a simultaneous look at a large number of response-determining genetic variants by applying the tools of pharmacogenomics, e.g. large-scale Single Nucleotide Polymorphism (SNP) detection and genotyping.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Relationship between adverse effects of antipsychotic treatment and dopamine D(2) receptor polymorphisms in patients with schizophrenia

Extrapyramidal adverse symptoms (EPS) represent a major type of adverse events in treatment with typical antipsychotic drugs which share high affinity to the dopamine D(2) receptor (DRD2). Genetic variants of this receptor may modulate the therapeutic response and the severity of adverse symptoms of antipsychotics. We analyzed nine known polymorphisms of the DRD2 in 665 schizophrenic patients with European Caucasian ethnic background and compared the intensity of acute dystonia, extrapyramidal symptoms, akathisia, and tardive dyskinesia between carriers of different DRD2 genotypes. In a subgroup of 40 patients with most severe extrapyramidal symptoms we sequenced the coding region including the exon-intron junctions of the DRD2 gene. Functionally relevant DRD2 amino acid variants (Ser(310), Cys(311)) were rare or were not found at all (Ala(96)). Complete sequence analysis of sufferers from the most severe adverse effects revealed two new intronic polymorphisms and a silent polymorphism in exon 7, but no new amino acid variants beyond those which are already known. We found no significant association between these polymorphisms and the intensity of the different types of adverse neurologic effects of the antipsychotics. These results were obtained by correlating adverse events with each of the nine single nucleotide polymorphisms and by correlation with the estimated haplotypes. In conclusion, genetic variations in the DRD2 gene were no major predictors of the individually variable adverse effects from antipsychotic treatment in Caucasian schizophrenic patients.

Relationship between functional dopamine D2 and D3 receptors gene polymorphisms and neuroleptic malignant syndrome

Our previous study has suggested that the TaqI A polymorphism of dopamine D2 receptor gene (DRD2) is associated with the predisposition to neuroleptic malignant syndrome (NMS). However, the specificity of this polymorphism as a predictor of NMS dose not seem to be sufficient enough. Meanwhile, it has been shown that the non-carriers of Del allele of the -141C Ins/Del polymorphism in the promoter region of DRD2 have lower dopamine D2 receptor in the brain than the carriers. In addition, dopamine D3 receptor gene has a Ser(9)Gly polymorphism, which may alter the receptor function. The present study examined the association between these three polymorphisms and the development of NMS to investigate if a combination of these polymorphisms could increase the specificity as markers for NMS. The subjects were 17 psychiatric patients who had developed NMS (13 patients with schizophrenia, 3 with major depression, and 1 with dementia of the Alzheimer's type) and 163 schizophrenic patients who had never developed this syndrome. The frequency of the A1 allele was significantly (P = 0.012) higher in the patients who had developed NMS (59%) than in the patients who had not (35%). The proportion of the A1 carriers was significantly (P = 0.003) higher in the patients with NMS (16/17: 94%) than in those without the syndrome (93/163: 57%). However, no significant differences were found in the allele and genotype frequencies of the other two polymorphisms between the two groups. The present study suggests that only the TaqI A polymorphism is at least partly useful as a predictor of NMS, but the -141 C Ins/Del and Ser(9)Gly polymorphisms are not.

Meta-analysis of genetic association studies supports a contribution of common variants to susceptibility to common disease

Association studies offer a potentially powerful approach to identify genetic variants that influence susceptibility to common disease, but are plagued by the impression that they are not consistently reproducible. In principle, the inconsistency may be due to false positive studies, false negative studies or true variability in association among different populations. The critical question is whether false positives overwhelmingly explain the inconsistency. We analyzed 301 published studies covering 25 different reported associations. There was a large excess of studies replicating the first positive reports, inconsistent with the hypothesis of no true positive associations (P < 10(-14)). This excess of replications could not be reasonably explained by publication bias and was concentrated among 11 of the 25 associations. For 8 of these 11 associations, pooled analysis of follow-up studies yielded statistically significant replication of the first report, with modest estimated genetic effects. Thus, a sizable fraction (but under half) of reported associations have strong evidence of replication; for these, false negative, underpowered studies probably contribute to inconsistent replication. We conclude that there are probably many common variants in the human genome with modest but real effects on common disease risk, and that studies using large samples will convincingly identify such variants.

D2 dopamine receptor gene in psychiatric and neurologic disorders and its phenotypes

The D2 dopamine receptor (DRD2) has been one of the most extensively investigated gene in neuropsychiatric disorders. After the first association of the TaqI A DRD2 minor (A1) allele with severe alcoholism in 1990, a large number of international studies have followed. A meta-analysis of these studies of Caucasians showed a significantly higher DRD2 A1 allelic frequency and prevalence in alcoholics when compared to controls. Variants of the DRD2 gene have also been associated with other addictive disorders including cocaine, nicotine and opioid dependence and obesity. It is hypothesized that the DRD2 is a reinforcement or reward gene. The DRD2 gene has also been implicated in schizophrenia, posttraumatic stress disorder, movement disorders and migraine. Phenotypic differences have been associated with DRD2 variants. These include reduced D2 dopamine receptor numbers and diminished glucose metabolism in brains of subjects who carry the DRD2 A1 allele. In addition, pleiotropic effects of DRD2 variants have been observed in neurophysiologic, neuropsychologic, stress response, personality and treatment outcome characteristics. The involvement of the DRD2 gene in certain neuropsychiatric disorders opens up the potential of a targeted pharmacogenomic approach to the treatment of these disorders.

Association of seven polymorphisms of the D2 dopamine receptor gene with brain receptor-binding characteristics

Association of alleles at the Taq1 A, Taq1 B, intron 6, Taq1 D, exon 7, exon 8, and promoter-141C sites of the D2 dopamine receptor gene with D2 dopamine receptor binding characteristics in the caudate nucleus of Caucasian alcoholic and nonalcoholic subjects was determined. For the Taq1 D, exon 7, exon 8, and promoter- 141C sites there were no significant allelic differences in Bmax (number of binding sites) or Kd (binding affinity) of the D2 dopamine receptors. However, subjects having the minor alleles at the Taq1 A, Taq1 B, and intron 6 sites had significantly lower Bmax than subjects not having them. None of these three polymorphisms had any significant effect on Kd. Highly significant linkage disequilibria were observed among the Taq1 A, Taq1 B, and intron 6 polymorphic sites, but linkage disequilibria between these three sites and each of the Taq1 D, exon 7, exon 8, and promoter-141C sites were of lesser or of no significance. Taken together, these findings suggest that the Taq1 A, Taq1 B, and intron 6 polymorphisms, but not the Taq1 D, exon 7, exon 8, and promoter-141C polymorphisms, are in linkage disequilibrium with a functional allelic variant that affects D2 dopamine receptor expression.

Gender-specific molecular heterosis of dopamine D2 receptor gene (DRD2) for smoking in schizophrenia

We examined the genetic effect of DRD2 A1 allele in 167 Korean schizophrenics in relation to their smoking habit. Although there was no apparent difference in the genotype distributions of DRD2 gene among the female schizophrenics (n = 66), the male counterpart (n = 101) showed significant differences in their genotype distributions. The comparison between male smoking and non-smoking patients showed the difference in genotype distribution (P = 0.010) with a higher prevalence of A1 allele (P = 0.020) and frequency of heterozygotes (P = 0.005), but not frequency of the A1 allele. The A1A2 heterozygotes male showed significantly higher smoking rate compared to the A1A1 or A2A2 homozygotes male, and non-smokers were deficient in heterozygotes. By contrast, among female schizophrenics, the heterozygotes showed a lower smoking rate than homozygotes and there were more heterozygotes in non-smokers. The deviation from Hardy-Weinberg expectations was observed in male and female non-smokers showing quite opposite profiles. Highly significant differences were seen between male and female non-smokers in A1 prevalence (P = 0.001), genotype distribution (P = 0.00011), and frequency of heterozygotes (P = 0.00003), but not in A1 frequency. The analyses from both male and female as one group showing no significant difference in the genotype distributions between smokers and non-smokers could be explained by the gender difference in the genetic effect of DRD2 A1 allele. Our findings present the gender-specific molecular heterosis of DRD2 gene in relation specifically to the smoking status of schizophrenic patients. They indicate the importance of heterosis and gender effects that should be taken into consideration for the association studies.

Tardive dystonia and genetic polymorphisms of cytochrome P4502D6 and dopamine D2 and D3 receptors: a preliminary finding

Tardive dystonia is an uncommon but intractable and distressing complication of neuroleptic treatment. It is suggested that individual predisposing vulnerability plays a major role in the development of the side effect. This study aimed to investigate relationship tardive dystonia and several genetic factors such as polymorphism of cytochrome P4502D6, and receptor polymorphisms of dopamine D(2) (TaqI A and -141C Ins/Del polymorphisms) and D(3) (Ser(9)Gly polymorphism). Nine patients with tardive dystonia were genotyped for these genetic polymorphisms. No specific genotypes or alleles were overpresented in the patients. This study suggests that these polymorphisms are not related to the development of tardive dystonia.

Indirect modulation of dopamine D2 receptors as potential pharmacotherapy for schizophrenia: III. Retinoids

Present antipsychotic drugs, whose clinical activity correlates with direct binding to dopamine D2 or other receptors, alleviate some of the symptoms of schizophrenia, but not all and not completely in many patients. In continuation of our overview of potential novel antipsychotic pharmacotherapy that would be based upon indirect modulation of dopamine or other neurotransmitter functioning, we focus in this article on the postulated use of retinoid analogs as novel antipsychotic agents. Several lines of evidence can be viewed as implicating retinoid dysregulation in schizophrenia, either as a causative or contributory factor. It has been proposed that using retinoid analogs to alter the downstream expression of dopamine D2 receptors might represent a novel approach to the treatment of the disease or amelioration of symptoms when used either as monotherapy or as adjunct pharmacotherapy to dopamine D2 receptor antagonists.

Allelic association analysis of the dopamine D2, D3, 5-HT2A, and GABA(A)gamma2 receptors and serotonin transporter genes with heroin abuse in Chinese subjects

Five candidate genes, the receptors DRD2, DRD3, HTR2A and GABA(A)gamma2, and the serotonin transporter (5-HTT) were analyzed for association with heroin abuse. We examined three polymorphisms (promoter - 141DeltaC, Ser311Cys, and TaqI) in the DRD2 gene, one polymorphism (Ser9Gly) in the DRD3 gene, two polymorphisms (promoter - 1438G/A and T102C) in the HTR2A gene, two polymorphisms (VNTR and Del/Ins) in 5-HTT gene, and one polymorphism (G3145A) in GABA(A)gamma2 gene in 121 Chinese heroin addicts and 194 controls. None of the polymorphisms differed significantly for allele, genotype, or haplotype frequencies, except for the DRD2 promoter polymorphism - 141DeltaC (genotype-wise and allele-wise, P = 0.05, uncorrected). An additional 344 subjects with heroin abuse and 104 controls were investigated for the - 141DeltaC polymorphism. In the second sample, there were no significant difference of genotype or allele frequencies between subjects with heroin abuse and normal controls. When we divided the sample by route of administration into nasal inhalers and IM or IV injectors, however, it produced a significant difference between inhalers of heroin and controls (genotype-wise, P = 0.006, allele-wise, P = 0.016) but not for injectors of heroin (genotype-wise, P = 0.81, allele-wise, P = 0.69). We also found that LD between all polymorphisms we examined in the gene was weak, possibly explaining why we see association of this polymorphism with heroin abuse but not with other markers in the gene. Overall our results indicates that the HTR2A, 5-HTT, DRD3 and GABA(A)gamma2 genes are not likely to be a major genetic risk factor for heroin abuse in this population, with the exception of possible association between nasal inhalation and DRD2 promoter - 141DeltaC polymorphism.

Nerve growth factor regulates dopamine D(2) receptor expression in prolactinoma cell lines via p75(NGFR)-mediated activation of nuclear factor-kappaB

Two groups of prolactinoma cell lines were identified. One group (responder) expresses both D(2) dopamine receptors and an autocrine loop mediated by nerve growth factor (NGF) and one group (nonresponder) lacks both D(2) receptors and NGF production. D(2) receptor expression in these cell lines is dependent on NGF. Indeed, NGF inactivation in responder cells decreases D(2) receptor density, while NGF treatment induces D(2) receptor expression in nonresponders. Here we show that inactivation of p75(NGFR), but not of trkA, resulted in D(2) receptor loss in responder cells and prevented D(2) receptor expression induced by NGF in the nonresponder. Analysis of nuclear factor-kappaB (NF-kappaB) nuclear accumulation and binding to corresponding DNA consensus sequences indicated that in NGF-secreting responder cells, but not in nonresponders, NF-kappaB is constitutively activated. Moreover, NGF treatment of nonresponder cells induced both nuclear translocation and DNA binding activity of NF-kappaB complexes containing p50, p65/RelA, and cRel subunits, an effect prevented by anti-p75(NGFR) antibodies. Disruption of NF-kappaB nuclear translocation by SN50 remarkably impaired D(2) receptor expression in responder cells and prevented D(2) gene expression induced by NGF in nonresponders. These data indicate that in prolactinoma cells the effect of NGF on D(2) receptor expression is mediated by p75(NGFR) in a trkA-independent way and that NGF stimulation of p75(NGFR) activates NF-kappaB, which is required for D(2) gene expression. We thus suggest that NF-kappaB is a key transcriptional regulator of the D(2) gene and that this mechanism may not be confined to pituitary tumors, but could also extend to other dopaminergic systems.

The influence on the schizophrenic symptoms by the DRD2Ser/Cys311 and -141C Ins/Del polymorphisms

The hyperactivity of dopaminergic systems is one of the major etiological hypotheses of schizophrenia. The major support for this hypothesis is that effective antipsychotic drugs bind to dopamine receptors and improve acute schizophrenic symptoms. For this reason, we investigated the allelic association between schizophrenia and polymorphisms of the DRD2 genes for the Ser/Cys311 and -141C Ins/Del. The subjects were 190 schizophrenics (120 males and 70 females) and 103 normal controls (53 males and 50 females). There were no significant differences between the patients and controls in the allele frequencies and the frequencies of the genotypes. We found no statistical association between schizophrenia and polymorphisms of the DRD2 genes for the Ser/Cys311 and -141C Ins/Del. These results indicate that the DRD2 gene may not develop schizophrenia. Next, we examined whether the genotypes influence the symptoms of schizophrenia the using Positive and Negative Symptom Scale scores. The Ser/Cys patients exhibited significantly lower positive and negative symptom scores than Ser/Ser patients. Patients with Del/Del, Ins/Del, or Ins/Ins showed higher positive symptom scores in descending order. This result suggested that the Del allele worsens the positive symptoms. We concluded that the DRD2 receptor gene may not influence the onset of schizophrenia, but there is a strong possibility that the Cys311 and -141C Del have a significant influence on the symptoms of schizophrenia.

New dopamine D2 receptor polymorphisms in rats and association with apomorphine-induced stereotypies

Adult Wistar rats injected with the dopamine receptor agonist apomorphine display different types of motility patterns with respect to oral stereotypes and locomotor activities. It was tested whether phenotypes exhibiting either 'sniffing' or 'non-sniffing' behaviour differed in gene structures of dopamine receptors D1 or D2. Forty-five Wistar rats of both genders were tested after a single dose of apomorphine (2 mg/kg s.c.) for stereotyped behaviour. Sequence analysis of the 5' flanking region, the 5' untranslated region and the coding region of the two genes revealed a new sequence for the 5' flanking region of the D1 receptor gene and two polymorphisms in the promoter region of the D2 receptor gene. The D2 receptor polymorphisms were denominated as T-355C- and A-257G-polymorphism. Between 'sniffing' and 'non-sniffing' animals no differences were detected in their D1 receptor sequence but there was a significant (P<0.05) association of the two phenotype groups with the D2 receptor genotype. These findings indicate that in Wistar rats at least part of an individual apomorphine stimulated behavioural phenotype might be due to an individual dopamine receptor D2 genotype.

Lack of association between a polymorphism in the promoter region of the dopamine D2 receptor and personality traits

Disturbances of the dopaminergic neurotransmitter system have been associated with a personality trait that involves novelty seeking. A functional polymorphism in the promoter region of the dopamine D2 receptor gene (DRD2) has been reported to be associated with schizophrenia. We examined the association between this polymorphism in the DRD2 promoter region and personality traits, as assessed with the Tridimensional Personality Questionnaire. No significant association emerged between the polymorphism in the DRD2 promoter region and personality traits. Entering sex and age as covariates in an analysis of covariance did not change the results. These data fail to confirm an association between a polymorphism in the promoter region of the DRD2 and personality traits.

Association between three functional polymorphisms of dopamine D2 receptor gene and tardive dyskinesia in schizophrenia

The dopamine D2 receptor (DRD2) gene is considered one of the candidate genes contributing to the development of tardive dyskinesia (TD). In the present study, we investigated the genetic association between three functional polymorphisms (Ser311Cys, -141C Ins/Del and TaqI A) in the DRD2 gene and TD (200 patients with schizophrenia: 44 with TD and 156 without TD). No significant difference in the allelic and genotypic distribution between patients with TD and those without TD was observed. However, we found a slightly significant association between the -141C Ins/Del polymorphism and the total Abnormal Involuntary Movement Scale (AIMS) score (P = 0.037). The significant association between the -141C Ins/Del polymorphism and the total AIMS score did not remain after the regression analysis was taken into account (P = 0.14). Our results suggest that that three functional polymorphisms in DRD2 may not play a major role in the occurrence of TD.

Genetic polymorphisms of the promoter region of dopamine D2 receptor and dopamine transporter genes and alcoholism among four aboriginal groups and Han Chinese in Taiwan

This study aims to examine the relationship between the functional polymorphism at the promoter region of the dopamine D2 receptor (DRD2) gene (i.e. -141C Ins/Del) and variable number of tandem repeat polymorphism at the 3' untranslated region of the dopamine transporter (DAT) gene (SLC6A3) with alcoholism in a case-control study. The cases (n = 203) were alcohol dependents with withdrawal symptoms, and the controls (n = 213) were sex- and ethnicity-matched individuals who were screened to exclude those with alcohol problems among four aboriginal groups (Atayal, Ami, Bunun, and Paiwan) and Han Chinese in Taiwan. To control for potential confounding factors, we excluded tobacco abusers from control subjects in part of the analysis and compared the distribution of the genetic polymorphisms in alcoholics with severe medical complications versus those with less severe medical complications. There were no differences in allele and genotype frequencies of these two distinct genetic markers between alcoholics and control subjects in these five different ethnic groups. There was no significant linkage disequilibrium between the -141C polymorphism and two other DRD2 polymorphisms (TaqI A and NcoI). The results remained unchanged when cases were limited to alcoholics with more severe medical complications or when tobacco abusers were excluded from control subjects. The results suggest that both the DRD2 promoter region and the DAT gene do not play a significant role in conferring vulnerability to alcoholism.

Imaging neurochemical endophenotypes: promises and pitfalls

A large number of polymorphisms in genes coding for neurotransmitter receptors and transporters have been associated with neuropsychiatric conditions, although few of these associations have been consistently replicated. These proteins are critical targets of psychoactive drugs and the clarification of the functional significance of these polymorphisms might offer important leads for drug development and therapeutic applications. Brain imaging techniques such as single photon emission computed tomography (SPECT) and positron emission tomography (PET) provide the means to monitor the expression and function of many of these proteins in the living human brain. This paper reviews brain imaging studies designed to evaluate the significance of polymorphisms in genes coding for important drug targets (e.g., the serotonin transporter [SERT], the dopamine transporter [DAT] and the dopamine D(2) receptor) in terms of expression or function. These studies illustrate the unique opportunities, as well as the pitfalls, generated by combining genetic analysis with brain imaging studies.

The -141C Ins/Del polymorphism in the dopamine D2 receptor gene promoter region is associated with anxiolytic and antidepressive effects during treatment with dopamine antagonists in schizophrenic patients

Previous studies have demonstrated a lower density of dopamine D2 receptor (DRD2) in subjects without Del alleles of the -141C Ins/Del polymorphism in DRD2 gene promoter region than in those with one or two Del alleles. The present study aimed to examine whether the -141C Ins/Del DRD2 promoter polymorphism is related to therapeutic response to selective DRD2 antagonists in the treatment of schizophrenia. Subjects consisted of 49 acutely exacerbated schizophrenic inpatients treated with bromperidol (30 cases, mean dose +/- SD: 11.4 +/- 4.8 mg/day) or nemonapride (19 cases, 18 mg/day). Clinical symptoms were evaluated by the Brief Psychiatric Rating Scale (BPRS) before and 3 weeks after the treatment. The -141C Ins/Del DRD2 genotypes, the Ins and Del alleles, were determined by a polymerase chain reaction method. Thirty-five patients were homozygous for the Ins allele and 14 were heterozygous for the Del and Ins alleles. The patients without Del allele showed a higher percentage of improvement in anxiety-depression symptoms than those with Del allele (58.5 +/- 44.5% versus 24.1 +/- 48.2%) after 3 weeks of treatment while percentage improvement in total BPRS or other subgrouped symptoms (positive, negative, excitement and cognitive symptoms) was similar between the two genotype groups. The present results suggest that the -141C Ins/Del DRD2 polymorphism is associated with anxiolytic and antidepressive effects of neuroleptic treatment in schizophrenic patients.

Genetic variations and polymorphisms of G protein-coupled receptors: functional and therapeutic implications

G protein-coupled receptors (GPCRs) represent a major class of proteins in the genome of many species, including humans. In addition to the mapping of a number of human disorders to regions of the genome containing GPCRs, a growing body of literature has documented frequently occurring variations (i.e. polymorphisms) in GPCR loci. In this article, we use a domain-based approach to systematically examine examples of genetic variation in the coding and noncoding regions of GPCR loci. Data to date indicate that residues in GPCRs are involved in ligand binding and coupling to G proteins and that regulation can be altered by polymorphisms. Studies of GPCR polymorphisms have also uncovered the functional importance of residues not previously implicated from other approaches that are involved in the function of GPCRs. We predict that studies of GPCR polymorphisms will have a significant impact on medicine and pharmacology, in particular, by providing new means to subclassify patients in terms of both diagnosis and treatment.

Association study of schizophrenia with polymorphisms at six candidate genes

Clinical studies have shown that there is a genetic contribution to the pathogenesis of schizophrenia. The molecular mechanisms of effective antipsychotic drugs and recent advances in neural development suggest that several dopamine receptor, serotonin receptor and neurotrophic factor genes might be involved in the disorder. In this study, we assessed the associations between schizophrenia and polymorphisms in the D2 and D3 dopamine receptor (DRD2, DRD3), the serotonin 2A receptor (5HTR2A), the brain-derived neurotrophic factor (BDNF), the ciliary neurotrophic factor (CNTF) and the neurotrophin-3 (NT-3) genes. Our results suggest that the polymorphisms at the DRD3, 5HTR2A, CNTF and BDNF gene loci are unlikely to make our sample more genetically susceptible to schizophrenia. However, we found significant differences in microsatellite allele frequencies between schizophrenic and control groups for DRD2 in the whole sample and for DRD2 and NT-3 only in women. Therefore, clinical differences in the presentation of schizophrenia between gender might be related to genetic factors.

Reproducible high efficiency gene transfer into Y79 retinoblastoma cells using adenofection

Several photoreceptor-specific genes are actively transcribed in Y79 retinoblastoma (Rb) cells, making this cell line potentially useful for the study of photoreceptor metabolism. The utility of these cells is limited because commonly used methods of gene transfer into Y79 cells are inefficient and lack reproducibility. In contrast, we found that adenovirus transduction yields high efficiency gene transfer, however, generation of recombinant adenovirus is lengthy and time consuming. Here, we show that adenofection, a method of coupling adenovirus to plasmid DNA for improved gene transfer, is efficient for gene delivery into Y79 cells. Recombinant adenovirus expressing bacterial lacZ was noncovalently complexed to GFP or luciferase reporter plasmids with polyethylenimine. Efficiency of plasmid gene delivery was determined by monitoring GFP fluorescence. For comparison, calcium phosphate-mediated or cationic lipid transfection was performed in Y79 and HEK293 cells using standard protocols. The adenofection protocol yielded significantly higher efficiencies in Y79 cells than that obtained in these cells with calcium phosphate or cationic lipids. This method will facilitate any experiment requiring reproducible high-level gene transfer. Here, we show that adenofection can be used to analyze activity of the rod photoreceptor PDE6A gene promoter.

Association analysis between two functional dopamine D2 receptor gene polymorphisms and schizophrenia

The dopamine D2 receptor (DRD2) gene has been listed as one of the candidate genes for susceptibility to schizophrenia. To date, a significant association between schizophrenia and two functional DRD2 gene polymorphisms, Ser311Cys and -141C Ins/Del, in Japanese samples, has been reported by Arinami et al. [1994: Lancet 343:703-704; 1997: Hum Mol Genet 6:577-582]. In the present study, we replicated the findings of Arinami et al. [1994: Lancet 343:703-704; 1997: Hum Mol Genet 6:577-582] in the same ethnic groups (Japanese samples) with the same polymorphisms (Ser311Cys and -141C Ins/Del). We genotyped these two polymorphisms for 241 patients and for 201 controls. Neither polymorphism was associated with schizophrenia. Moreover, in a haplotype analysis of the present sample, combined pairs of two polymorphisms provided no evidence for the association of either haplotype with schizophrenia. Our findings indicate that an association between the two functional DRD2 gene polymorphisms, Ser311Cys and -141C Ins/Del, and schizophrenia is unlikely.

The -141C Ins/Del polymorphism of the dopamine D2 receptor gene is not associated with either migraine or Parkinson's disease

Abnormalities in dopamine neurotransmission at the dopamine D2 receptor (DRD2) have been implicated in both migraine and Parkinson's disease. Positive associations have also been found between polymorphisms within the DRD2 gene and both of these conditions. The -141C Ins/Del polymorphism in the DRD2 receptor gene is a putative functional polymorphism. The purpose of this study was to determine whether it and any genes in linkage disequilibrium with this marker are involved in either of these conditions. We have compared the genotype and allele frequencies of the -141C Ins/Del polymorphism in 200 migraineurs and 260 Parkinson's disease cases with 464 controls. We have found no association between the receptor gene and either condition (P = 0.89 and P = 0.56 respectively). Our findings do not support the hypothesis that this polymorphism is involved in the aetiology of migraine or Parkinson's disease.

No relationship between--141C Ins/Del polymorphism in the promoter region of dopamine D2 receptor and extrapyramidal adverse effects of selective dopamine D2 antagonists in schizophrenic patients: a preliminary study

Previous studies have shown that subjects without Del alleles of the--141C Ins/Del polymorphism in the promoter region of the dopamine D2 receptor (DRD2) gene have lower DRD2 density that those with one or two Del alleles. The present study aims to investigate the relationship between the -141C Ins/Del polymorphism and extrapyramidal adverse effects of bromperidol and nemonapride, antipsychotic drugs with a selective and potent DRD2 antagonistic property, in schizophrenic inpatients. Twenty-seven patients were treated with bromperidol at a fixed-dose of 6, 12 or 18 mg/day, and 25 patients were treated with nemonapride at a fixed-dose of 18 mg/day. The duration of treatment with these drugs was 3 weeks. The Ins and Del alleles were determined by PCR. Extrapyramidal adverse effects were assessed by the Udvalg for Kliniske Undersøgelser side effects rating scale. The subjects consisted of 38 homozygotes of the Ins allele and 14 heterozygotes of the Ins and Del alleles. There were no significant differences in the incidence or severity of extrapyramidal adverse effects between patients with and without the Del allele. It is possible that this result was due to a lack of statistical power. However, the present study suggests that the--141C Ins/Del polymorphism is not related to the development of extrapyramidal adverse effects during acute-phase treatment with antidopaminergic agents.

Polymorphisms in dopamine receptors: what do they tell us?

Many genetic studies have focussed on dopamine receptors and their relationship to neuropsychiatric disease. Schizophrenia, bipolar disorder, and substance abuse have been the most studied, but no conclusive linkage or association has been found. The possible influence of dopamine receptor variants on drug response has not received as much attention. While there is some evidence that polymorphisms and mutations in dopamine receptors can alter functional activity and pharmacological profiles, no conclusive data link these gene variants to drug response or disease. The lack of unequivocal findings may be related, in part, to the subtle changes in receptor pharmacology that these polymorphisms and mutations mediate. These subtle effects may be obscured by the influence of genes controlling drug metabolism and kinetics. Further insight into the pharmacogenetics of dopamine receptors may require not just more studies, but novel approaches to the study of complex genetic traits and diseases.

Pharmacogenomics and schizophrenia

Although antipsychotic drugs are effective in alleviating schizophrenic symptoms, individual differences in patient response suggest that genetic components play a major role, and pharmacogenetic studies have indicated the possibility for a more individually based pharmacotherapy. The new field of pharmacogenomics, which focuses on genetic determinants of drug response at the level of the entire human genome, is important for development and prescription of safer and more effective individually tailored drugs. DNA microarray (DNA chip) analysis enables genome-wide scanning, using the high-density single nucleotide polymorphisms map. Pharmacogenomics will aid in understanding how genetics influence disease development and drug response, and contribute to discovery of new treatments. The rate of discovery of those polymorphisms will depend on the quality of the drug response phenotype. Prospective genotyping of schizophrenic patients for the many genes at the level of the drug target, drug metabolism, and disease pathways will contribute to individualized therapy matching the patient's unique genetic make-up with an optimally effective drug.

Polymorphisms in genes involved in neurotransmission in relation to smoking

Smoking behavior is influenced by both genetic and environmental factors. The genetic contribution to smoking behavior is at least as great as its contribution to alcoholism. Much progress has been achieved in genomic research related to cigarette-smoking within recent years. Linkage studies indicate that there are several loci linked to smoking, and candidate genes that are related to neurotransmission have been examined. Possible associated genes include cytochrome P450 subfamily polypeptide 6 (CYP2A6), dopamine D(1), D(2), and D(4) receptors, dopamine transporter, and serotonin transporter genes. There are other important candidate genes but studies evaluating the link with smoking have not been reported. These include genes encoding the dopamine D(3) and D(5) receptors, serotonin receptors, tyrosine hydroxylase, trytophan 2,3-dioxygenase, opioid receptors, and cannabinoid receptors. Since smoking-related factors are extremely complex, studies of diverse populations and of many aspects of smoking behavior including initiation, maintenance, cessation, relapse, and influence of environmental factors are needed to identify smoking-associated genes. We now review genetic polymorphisms reported to be involved in neurotransmission in relation to smoking.

Family-based study of DRD2 alleles in alcohol and drug dependence

Numerous case-control studies have addressed the hypothesis that variant alleles of the dopamine D2 receptor gene (DRD2) increase the liability for alcohol and/or drug dependence, and both positive and negative results have been reported. Because population frequencies of these alleles vary considerably, the conflicting results could be due to population stratification bias. Using the transmission disequilibrium test, the present study examined linkage disequilibrium of alcohol and drug (opioid and/or cocaine) dependence with three DRD2 polymorphic systems: (a) TaqI A, (b) TaqI D, and (c) the functional -141CIns/Del promoter systems. DNA samples were collected from small nuclear families (SNFs), where one or more offspring met DSM-III-R or DSM-IV criteria for alcohol and/or drug dependence. Because positive association between DRD2 alleles and alcohol and/or drug dependence has been reported only in populations of European ancestry, we limited the present study to European Americans (EAs). No evidence for linkage disequilibrium was found for any of the polymorphic systems when examined in relation to any substance dependence, alcohol dependence (with or without drug dependence), or drug dependence (with or without alcohol dependence). These results are consistent with those from a recent family-based study of alcohol dependence. Together, these studies suggest that the conflicting findings from case-control studies of the association between alleles of DRD2 and substance dependence may be attributable to population stratification in some samples.

Haplotypes at the DRD2 locus and severe alcoholism

Association studies of the minor TaqI A allele of the D(2) dopamine receptor (DRD2) gene with alcoholism have produced conflicting findings. Failure to assess alcoholics for severity of their disorder and to screen controls for substance use have been proposed as causes for the discrepant results. In the present study, five diallelic sites spanning the DRD2 gene were determined in combined Caucasian (non-Hispanic) studies of more severe alcoholics (n = 92) and controls screened for substance use (n = 85). The frequency of the minor alleles at the 3'-untranslated site (TaqI A) and two intronic sites (TaqI B and intron 6) of the DRD2 gene were each strongly associated with alcoholism. Moreover, the alcoholics compared with the controls at these three sites had a significantly higher frequency of the minor/major allele heterozygote haplotype combination (A1/A2 B1/B2 T/G) than the major allele homozygote haplotype combination (A2/A2 B2/B2 G/G). However, exon 7 and promoter alleles were not associated with alcoholism. In neither the alcoholics nor in the controls were there departures from Hardy-Weinberg equilibrium at any of the five sites examined. The most significant diallelic composite genotypic disequilibria were found when comparisons were made between TaqI A and TaqI B, TaqI A and intron 6, and TaqI B and intron 6 sites. Weaker but still significant disequilibria were observed when TaqI A and exon 7, TaqI B and exon 7, intron 6 and exon 7, and promoter and exon 7 sites were compared. However, no significant disequilibria were noted when TaqI A and promoter, TaqI B and promoter, and intron 6 and promoter sites were compared. In sum, the study found significant evidence for association of the minor alleles in the untranslated sites of the DRD2 gene and their haplotypes with the more severe alcoholic phenotype.

Single nucleotide polymorphisms and the future of genetic epidemiology

In this review, we consider the motivation behind contemporary single nucleotide polymorphism (SNP) initiatives. Many of these initiatives are projected to involve large, population-based surveys. We therefore emphasize the utility of SNPs for genetic epidemiology studies. We start by offering an overview of genetic polymorphism and discuss the historical use of polymorphism in the identification of disease-predisposing genes via meiotic mapping. We next consider some of the unique aspects of SNPs, and their relative advantages and disadvantages in human population-based analyses. In this context, we describe and critique the following six different areas of application for SNP technologies: Gene discovery and mapping. Association-based candidate polymorphism testing. Diagnostics and risk profiling. Prediction of response to environmental stimuli, xenobiotics and diet. Homogeneity testing and epidemiological study design. Physiologic genomics. We focus on key issues within each of these areas in an effort to point out potential problems that might plague the use of SNPs (or other forms of polymorphism) within them. However, we make no claim that our list of considerations are exhaustive. Rather, we believe that they may provide a starting point for further dialog about the ultimate utility of SNP technologies. In addition, although our emphasis is placed on applications of SNPs to the understanding of human phenotypes, we acknowledge that SNP maps and technologies applied to other species (e.g. the mouse genome, pathogen genomes, plant genomes, etc.) are also of tremendous interest.

Association between Taq1 a dopamine D2 receptor polymorphism and psychopathology of schizophrenia in Japanese patients

1. Previous reports showed that the A1 allele of Taq1 A dopamine D2 receptor polymorphism was associated with lowered density and diminished function of dopamine D2 receptor. In this study, association between Taq1 A dopamine D2 receptor polymorphism and psychopathology of schizophrenia was investigated. 2. The subjects were 61 acutely exacerbated schizophrenic patients who were all Japanese descent and had received no medication for at least one month before this study. Pretreatment psychotic symptoms were assessed by the Brief Psychiatric Rating Scale (BPRS). The Taq1 A genotypes, the A1 and A2 alleles, were determined by polymerase chain reaction method. 3. The patients were divided into three genotype groups; i.e., the patients with A1/A1 allele (n=6), those with A1/A2 allele (n=32) and those with A2/A2 allele (n=23). 4. There was no significant difference in total BPRS, subgrouped symptoms (positive, negative, anxiety-depression, excitement and cognitive symptoms) or any scores of BPRS items among the three Taq1 A genotype groups. 5. The present study suggests that Taq1 A dopamine D2 receptor polymorphism does not play an important role in psychopathological symptoms of schizophrenia.