Dopamine D1 receptor gene polymorphism and schizophrenia in Japan

Understanding the Role of Dopamine in Cancer: Past, Present, and Future

Dopamine (DA, 3-hydroxytyramine) is member of the catecholamine family and is classically characterized according to its role in the central nervous system as a neurotransmitter. In recent decades, many novel and intriguing discoveries have been made about the peripheral expression of DA receptors (DRs) and the role of DA signaling in both normal and pathological processes. Drawing from decades of evidence suggesting a link between DA and cancer, the DA pathway (DAP) has recently emerged as a potential target in antitumor therapies. Due to the onerous, expensive, and frequently unsuccessful nature of drug development, the repurposing of dopaminergic drugs for cancer therapy has the potential to greatly benefit patients and drug developers alike. However, the lack of clear mechanistic data supporting the direct involvement of DRs and their downstream signaling components in cancer represents an ongoing challenge that has limited the translation of these drugs to the clinic. Despite this, the breadth of evidence linking DA to cancer and non-tumor cells in the tumor microenvironment (TME) justifies further inquiry into the potential applications of this treatment modality in cancer. Herein, we review the literature characterizing the interplay between the DA signaling axis and cancer, highlighting key findings, and then propose rational lines of investigation to follow.

Association of dopamine D1 receptor gene polymorphism with schizophrenia: a meta-analysis

To date, the role of dopamine D1 receptor (DRD1) polymorphism in schizophrenia remains controversial. We carried out a meta-analysis to determine whether DRD1 polymorphism influences the risk of schizophrenia. We examined whether rs4532 and rs5326 genetic variants are related to the etiology of schizophrenia, using a meta-analysis. Relevant case-control studies were retrieved by database searching and selected according to established inclusion criteria. A total of ten studies were identified and included in our meta-analysis, nine for rs4532, with 1,941 cases and 2,480 controls, and four for rs5326, with 1,285 cases and 1,195 controls. No significant association was found between the rs4532 locus and schizophrenia. For the rs5326 locus, the guanine-adenine (GA) genotype was associated with schizophrenia as a risk factor (for GA vs guanine-guanine [GG], odds ratio [OR] =1.36, 95% confidence interval [CI]: 1.15-1.61, P<0.001). The GA genotype of rs5326 increased the risk of schizophrenia, but there was no association between rs4532 and schizophrenia. These data may provide references for case-control studies in schizophrenia in future.

Sexually dimorphic interaction between the DRD1 and COMT genes in schizophrenia

Dopaminergic dysfunction in the prefrontal cortex (PFC) is involved in the pathophysiology of schizophrenia. In the PFC, dopamine signalling largely depends on the D1 receptors, which are coded by the DRD1 gene, and on the regulation of dopamine levels by the enzyme catechol-O-methyltransferase (COMT). Here, we investigate the role of DRD1 and its interaction with the COMT gene in schizophrenic patients. In two gender-limited independent patient and control samples, we genotype five Tag single nucleotide polymorphisms (tagSNPs) of DRD1. The DRD1 SNP and haplotype associations, as well as interaction effects with the Val158Met COMT SNP were analyzed. In the male sample, we found the rs11746641 and rs11749676 DRD1 SNPs were associated with schizophrenia. Haplotype analyses identified the T-A-T-C-T variant related to a protective effect (P = 0.008) and the G-G-T-C-C variant that showed a tendency to be a risk factor for the disorder (P = 0.012). A logistic regression analysis revealed a significant pattern of interaction between DRD1 and COMT for both the rs11746641 (P = 0.002) and rs11749676 (P = 4.5 x 10(-5)) SNPs. DRD1-associated haplotypes were exclusively related to schizophrenia in the Val homozygous subgroup of patients (T-A-T-C-T: P = 0.003; G-G-T-C-C: P = 0.006). In females, none of the DRD1 SNPs were linked to the disorder. Our genetic data suggest that DRD1 and COMT are epistatically associated with protection against and the risk of developing schizophrenia in a gender-dependent fashion, and support the role of dopamine dysfunction at the PFC in the pathophysiology of this disorder.

No genetic association between dopamine D1 receptor gene and [early onset] schizophrenia

Decreased dopaminergic activity in the prefrontal cortex (PFC) has been consistently reported in schizophrenia patients. The dopamine D1 receptor (DRD1) plays an important role in mediating dopaminergic transmission in the PFC. Controversy about this topic still exists despite ample evidence suggesting that the DRD1 gene is associated with performance on neuropsychological tests probing the function of the PFC in schizophrenia, as well as positive and negative symptoms and therapeutic response to antipsychotics. To determine whether this gene is involved in the etiology of schizophrenia, we undertook a case-control study to look for an association. We genotyped five single nucleotide polymorphisms (SNPs) rs4532, rs5326, rs2168631, rs6882300 and rs267418 within the DRD1 involving 373 schizophrenia patients with early age of onset and 379 healthy subjects. No significant differences of genotype, allele or haplotype distribution were identified between patients and controls. Our results do not preclude a possible role of DRD1 in the etiology of schizophrenia. As an important dopaminergic gene, DRD1 may contribute to schizophrenia by interacting with other genes. Further relevant studies are warranted.

Polymorphisms in dopamine receptor DRD1 and DRD2 genes and psychopathological and extrapyramidal symptoms in patients on long-term antipsychotic treatment

DRD(1) and DRD(2) receptor gene variants have been associated with clinical aspects of schizophrenia; however only specific features were analyzed in different samples. To assess the complex interaction between genetic and clinical factors, we studied the possible cross-interactions between DRD1 and DRD2 dopamine receptor gene polymorphisms, symptomatology of schizophrenia and schizoaffective disorders, and the occurrence of treatment induced side effects taking into consideration possible clinical confounding variables. One hundred thirty one outpatients in stable remission meeting the DSMIV criteria for schizophrenia spectrum disorders and receiving long-term maintenance therapy with haloperidol, fluphenazine, zuclopenthixole, or risperidone were genotyped for DRD1 A-48G, DRD2 Ins-141CDel, and DRD2 Ser311Cys polymorphisms. Psychopathological symptoms were assessed with the positive and negative syndrome scale for schizophrenia (PANSS). Extrapyramidal side effects were assessed with the Simpson-Angus extrapyramidal side effects scale (EPS), the Barnes Akathisia scale (BARS), and the abnormal involuntary movement scale (AIMS). Drug dosage was included as covariant because it was associated with the severity of symptomatology, akathisia, and parkinsonism. No association was observed for DRD1 and DRD2 polymorphisms and extrapyramidal side effects, or with the other clinical variables considered. Our study suggests that DRD1 and DRD2 variants are not liability factors for tardive dyskinesia.

5′ UTR polymorphism of dopamine receptor D1 (DRD1) associated with severity and temperament of alcoholism

Multiple dopamine receptors in the dopaminergic system may be prime candidates for genetic influence on alcohol abuse and dependence due to their involvement in reward and reinforcing mechanisms. Genetic polymorphisms in dopamine receptor genes are believed to influence the development and/or severity of alcoholism. To examine the genetic effects of the Dopamine Receptor D1 (DRD) gene family (DRD1-DRD5) in the Korean population, 11 polymorphisms in the DRD gene family were genotyped and analyzed in 535 alcohol-dependent subjects and 273 population controls. Although none of the polymorphisms of DRD1-5 genes were found to be associated with the risk of alcoholism, one 5' UTR polymorphism in the DRD1 (DRD1-48A>G) gene was significantly associated with severity of alcohol-related problem, as measured by the Alcohol Use Disorders Identification Test (AUDIT) in a gene dose-dependent manner, i.e., 24.37 (+/-8.19) among patients with -48A/A genotype, 22.37 (+/-9.49) among those with -48A/G genotype, and 17.38 (+/-8.28) among those with -48G/G genotype (P=0.002). The genetic effects of DRD1-48A>G were further analyzed with other phenotypes among alcohol-dependent subjects. Interestingly, the DRD1-48A>A genotype was also found to be associated with novelty seeking (NC), harm avoidance (HA), and persistence (P) (P =0.01, 0.02, and 0.003, respectively). The information derived from this study could be valuable for understanding the genetic factors involved in alcoholic phenotypes and genetic distribution of the DRD gene family, and could facilitate further investigation in other ethnic groups.

Genetic mouse models of schizophrenia: from hypothesis-based to susceptibility gene-based models

Translation of human genetic mutations into genetic mouse models is an important strategy to study the pathogenesis of schizophrenia, identify potential drug targets, and test new drugs for new antipsychotic treatments. Although it is impossible to recapitulate the full spectrum of schizophrenia symptoms in animal models, hypothesis-driven genetic mouse models have been successful in reproducing several schizophrenia-like behaviors and uncovering the roles of specific genes in dopamine and glutamine neurotransmission systems in mediating schizophrenia-like behaviors. Recent discoveries of susceptibility genes for schizophrenia and recognition of cognitive dysfunction as a core feature of schizophrenia and a phenotype of susceptibility for schizophrenia offer opportunities to develop newer genetic mouse models based on susceptibility. This new generation of genetic mouse models could shed light on the etiology of schizophrenia and lead us to new hypotheses, novel diagnostic tools, and more effective therapy.

Dopamine receptor D1 gene -48A/G polymorphism is associated with bipolar illness but not with schizophrenia in a Polish population

Dysregulation of dopaminergic neurotransmission has been implicated in the etiology of major psychoses. The dopamine D(1) receptor (DRD1) plays a role in some brain functions and mechanisms of psychotropic drugs. Therefore, the DRD1 gene makes a good candidate gene for molecular genetic studies in schizophrenia and bipolar affective disorder. In the present study, the -48A/G polymorphism of the DRD1 gene was estimated in patients with schizophrenia (n=407) or bipolar affective disorder (n=380), and in healthy controls (n=399). No association was found between the polymorphism studied and schizophrenia, either in the whole group of patients or in subgroups divided by gender, age at onset or predominance of positive or negative symptoms. A statistical trend was obtained for an association between this polymorphism and bipolar affective disorder (p=0.059 for genotypes, p=0.073 for alleles). The G/G genotype and G allele were significantly more frequent in patients with bipolar disorder, type II (p=0.016 for genotypes, p=0.008 for alleles), especially in the women subgroup (p=0.054 for genotypes, p=0.024 for alleles). An association between the G/G genotype and bipolar affective disorder with disease onset after 18 years of age was also found (p=0.022). These data suggest that the -48A/G polymorphism of the DRD1 gene may be involved in the etiology of bipolar disorder in a Polish population.

Association between dopamine receptor D1 A-48G polymorphism and methamphetamine abuse

Several lines of evidence have suggested that substance abuse is mediated by the dopaminergic rewarding system, primarily through the activity of the dopamine receptor D1 (DRD1). The purpose of the present study was to evaluate the association of DRD1 A-48G polymorphism with methamphetamine (MAP) abusers and MAP-induced psychosis patients. A total of 363 MAP abusers and 425 healthy normal controls were enrolled. The structural Diagnostic Interview for Genetic Study was used to evaluate all MAP abusers. The MAP abusers were classified into psychosis (n = 135) and non-psychosis (n = 228) groups. A-48G polymorphism was determined by polymerase chain reaction-restriction fragment length polymorphism. The results show that male sex and a higher frequency of MAP abuse were the predisposing factors in the development of MAP psychosis. The DRD1 -48G allele frequency in the MAP psychosis group, non-psychosis group and the healthy normal controls was 0.14, 0.18 and 0.16, respectively. No association was found between DRD1 A-48G polymorphism and MAP abuse and MAP psychosis. However, the data provided additional evidence of ethnicity-related differences in the distribution of polymorphism in comparison to previous studies.

Major affective disorders and schizophrenia: a common molecular signature?

Psychiatric disorders, including affective disorders (AD) and schizophrenia (SZ) are among the most common disabling brain diseases in Western populations and result in high costs in terms of morbidity as well as mortality. Although their etiology and pathophysiology is largely unknown, family-, twin-, and adoption studies argue for a strong genetic determination of these disorders. These studies indicate that there is between 40 and 85% heritability for these disorders but point also to the importance of environmental factors. Therefore, any research strategy aiming at the identification of genes involved in the development of AD and SZ should account for the complex nature (multifactorial) of these disorders. During the last decade, molecular genetic studies have contributed a great deal to the identification of genetic factors involved in complex disorders. Here we provide a comprehensive review of the most promising genes for AD and SZ, and the methods and approaches that were used for their identification. Also, we discuss the current knowledge and hypotheses that have been formulated regarding the effect of variations on protein functioning as well as recent observations that point to common molecular mechanisms.

An association study of dopamine receptors polymorphisms and the Wisconsin Card Sorting Test in schizophrenia

Dopamine (DA), an important neurotransmitter in prefrontal cortex (PFC), is involved in the pathogenesis of schizophrenia. The aim of the study was to test an association between common polymorphism of genes for DA receptors DRD1, DRD2, DRD3, DRD4, and performance on the Wisconsin Card Sorting Test (WCST), measuring various functions of PFC, in 138 schizophrenic patients. Patients with G/G genotype of DRD1 tended to obtain worse results in all domains of WCST compared to patients with remaining genotypes, particularly for number of completed corrected categories, and trials to set the first category. A relationship was also found in female patients between DRD2 polymorphism and number of perseverative errors, while no association between WCST results and DRD3 or DRD4 polymorphism was observed in patients studied. The results may suggest an association between DRD1 gene polymorphism and performance on PFC test in schizophrenia. Also, the gender-dependent role of DRD2 in this process may be presumed.

Pharmacogenomics and renal drug disposition in the newborn

Genetic polymorphisms in the genes coding for drug metabolizing enzymes, drug transporters, and drug receptors are major determinants of an individual's response to drugs. The potential interactions of pharmacogenomics of renal drug transporters and drug receptors with renal drug disposition and the immature kidneys are briefly reviewed. Examples of gene polymorphisms seen in the RAAS (renin angiotensin system), beta-adrenergic receptors, dopamine receptors and cytochrome P450 and their potential clinical impact are discussed. The human newborn has deficient hepatic and renal drug metabolism and disposition. This immaturity in drug-handling capacity may potentially be superimposed to genetic polymorphisms determining drug metabolism and transport thereby substantially increasing interpatient variability in drug dose requirements and in drug responses in the newborn. Pharmacogenomics is a tool that can be used to individualize drug therapy in newborns to minimize adverse drug effects and to optimize efficacy.

Catalog of 178 variations in the Japanese population among eight human genes encoding G protein-coupled receptors (GPCRs)

We screened DNAs from 48 Japanese individuals for single-nucleotide polymorphisms (SNPs) in eight genes encoding G protein-coupled receptors (GPCRs) by directly sequencing the entire relevant genomic regions except for repetitive-sequence elements. This approach identified 147 SNPs and 31 insertion/deletion polymorphisms among the eight GPCR genes. On average, we identified one SNP in every 584 nucleotides. Of the 147 SNPs, 69 were identified in AGTR1, 12 in AGTR2, nine in AGTRL1, 20 in AVPR1A, nine in AVPR2, 16 in DRD1, six in ITGA2B, and six in PTGIR. Twenty-one SNPs were located in 5' flanking regions, 76 in introns, 32 in exons, and 18 in 3' flanking regions. These variants should contribute to investigations of possible correlations between genotypes and phenotypes as regards susceptibility to disease or responsiveness to drug therapy.

Early-onset schizophrenia and dopamine-related gene polymorphism

Schizophrenic patients with an onset before age 16 years (early-onset schizophrenia, EOS) would be a rare but attractive subpopulation for genetic studies. This study explored the relationship between the polymorphism of four dopamine-regulating-enzymes (tyrosine hydroxylase, dopamine-beta-hydroxylase, catechol-O-methyltransferase, monoamine oxidase-A) genes, four dopamine-receptors (dopamine D1, D2, D3, D4 receptors) genes and susceptibility to EOS in a Japanese sample. Subjects comprised 51 Japanese patients who met DSM-IV criteria for schizophrenia with an onset before age 16 (by age 15) and 148 Japanese healthy controls. DNA was extracted from whole blood and genotyping was carried out by PCR-RELP using each restriction endonuclease. No significant difference was found in the allele frequencies or genotype distributions of any of the eight genes examined between EOS and the control groups. We did not find the relationship between the polymorphism of eight dopamine-related genes and susceptibility to EOS in a Japanese sample.

Molecular genetics of schizophrenia: past, present and future

Schizophrenia is a severe neuropsychiatric disorder with a polygenic mode of inheritance which is also governed by non-genetic factors. Candidate genes identified on the basis of biochemical and pharmacological evidence are being tested for linkage and association studies. Neurotransmitters, especially dopamine and serotonin have been widely implicated in its etiology. Genome scan of all human chromosomes with closely spaced polymorphic markers is being used for linkage studies. The completion and availability of the first draft of Human Genome Sequence has provided a treasure-trove that can be utilized to gain insight into the so far inaccessible regions of the human genome. Significant technological advances for identification of single nucleo-tide polymorphisms (SNPs) and use of microarrays have further strengthened research methodologies for genetic analysis of complex traits. In this review, we summarize the evolution of schizophrenia genetics from the past to the present, current trends and future direction of research.

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.