Alleles at the dopamine D4 receptor locus do not contribute to the genetic susceptibility to schizophrenia in a large Swedish kindred

The discovery of a functional polymrphism within the dopamine D₄ receptor gene (DRD4) has not only strengthened the hypotheses implicating DRD4 in the etiology of neuropyschiatic disorders, but also provided a genetic marker for testing these hypotheses. The possibility of the dopamine D₄ receptor as a candidate gene for schizophrenia was investigated in a large Swedish kindred segregating for schizophrenia. Linkage to schizophrenia was tested by linkage analyses of 6 polymorphic markers (at 4 loci) in chromosome 11p15.5 including the dopamine D₄ receptor (DRD4) and the tyrosine hydroxylase (TH) loci. Schizophrenia was excluded from close linkage to the DRD4 locus using two of the polymorphisms located within the dopamine D₄ receptor gene. The first DRD4 polymorphism consists of variation in the number of a 48 bp imperfect direct repeat in the third exon; the second consists of a variable number of repeated G nucleotides in the first intron. In addition, some of the individuals homozygous for four or seven copies of 48 bp repeat alleles were tested for previously reported sequence variation among repeats. No single haplotype of the DRD4 alleles or haplotype of other markers in chromosome 11p15.5 was found to be common to the schizophrenic individuals in this family. Therefore, we find no evidence for linkage of the D₄ receptor, or this region of 11p15.5, with genetic susceptibility to schizophrenia in this kindred. © 1993 Wiley-Liss, Inc.     

精神分裂症与六种候选功能基因的关联研究

目的：探讨多巴胺D2受体基因（dopamine D2 receptor,DRD2)、多巴胺D4受体基因（DRD4）、5－羟色胺2A受体基因（5－hydroxytryptamine 2A receptor,5-HT2A),5-羟色胺6受体基因（5－HT6)、儿茶酚胺氧位甲基转移酶基因（catechol-O-methyltransferase,COMT)和多巴胺转运体基因（dopamine transferase,DAT1)多态性与精神分裂症的关系。方法：应用基因扩增片段长度多态和基因扩增的限制性片段长度多态技术，对中国汉族人群中67例精神分裂症患者与上述6种候选功能和基因扩增的限制性片段长度多态技术，对中国汉族人群中67例精神分裂症患者与上述6种候选功能基因进行遗传关联分析。结果：（1）DRD2、5－HT2A、5－HT6和KCOMT的基因型和等位基因频率在患者组和对照组中差异无显著性（P＞0．05）。（2）DRD4基因中6次重复序列等位基因、DAT1基因中480bp等位基因和480／520基因型在两组中差异有显著性，Z分别为2．03、2．05和2．05；P均小于0．05。（3）经关联分析后，仅DAT1基因的480bp等位基因的比值比为0．441，95％可信区间为0．202－0．963，并有显著性意义（Z＝2．05，P＜0．05），而DAT1的480／520基因型和DRD4和6次重复序列等位基因的比值比分别为0．128和0．123，但Z均小于1．96，无显著性意义（P＞0．05）。因此，6个功能基因中仅DAT1的480bp等位基因与精神分裂症呈负关联。结论：中国汉族人群中DAT1基因的480bp等位基因与精神分裂症间存在负关联，支持精神分裂症的多巴胺假说。     

Further evidence of no association between Ser9Gly polymorphism of dopamine D3 receptor gene and schizophrenia

Dopamine D3 receptor (DRD3) was demonstrated to have important implications in schizophrenia, because it binds antipsychotic drugs and is abundant in the limbic system of the brain. Several groups attempted to find an association between a serine-to-glycine polymorphism at codon 9 of the DRD3 gene (Ser9Gly) and schizophrenia; however, the results were inconsistent. We conducted a case-control association study in Han Chinese schizophrenic patients from Taiwan, to examine the relationship of this serine-to-glycine polymorphism and schizophrenia. We noted no significant differences of genotype distribution, allele frequencies, or homozygosity proportion of this polymorphism between schizophrenic patients (N = 178) and controls (N = 100). When patients were divided according to sex, or presence or absence of family history, the differences were still not significant. Our study does not support the contention that the Ser9Gly polymorphism of the DRD3 gene plays a major role in schizophrenia. Am. J. Med. Genet. 74:40–43, 1997. © 1997 Wiley-Liss, Inc.     

多巴胺D3受体基因Ser-9-Gly多态性精神分裂症的关联研究

为探讨精神分裂症与多巴胺 D3受体基因 ( dopamine D3receptor gene,DRD3) Ser-9-Gly多态性是否关联。应用PCR-RFLP方法检测了广州地区汉族人群中 1 2 3例家族史阴性、1 1 3例家族史阳性精神分裂症患者、1 6 8例家族史阴性患者父母和 4 7例正常老年人中多巴胺 D3受体基因 Ser-9-Gly多态性 ,并对多巴胺 D3受体基因各等位基因及基因型与精神分裂症进行了相关分析 ,DRD3与精神分裂症、患者性别及家族史均无关联 ( P>0 .0 5 )。提示广州地区汉族人群中DRD3基因 Ser-9-Gly多态性与精神分裂症没有关联。     

多巴胺D4受体第3外显子48 bp可变重复序列多态性与抽动障碍的传递不平衡检测

目的研究多巴胺D4受体第3外显子48 bp可变重复序列(DRD4 exonⅢ48bpVNTR)多态性是否与抽动障碍(tic disorder, Tic)存在关联.方法采用国际标准化的<Tourette综合征及其相关疾病遗传研究定式检查提纲>收集病史,运用核心家系传递不平衡分析方法(transmission disequilibrium test, TDT)对122个核心家系进行关联分析,根据是否合并注意缺陷多动障碍(attention deficit and hyperactivity disorder, ADHD),将122个核心家系分为合并ADHD的抽动障碍组[合并ADHD的Tourette综合征(Tourette syndrome, TS)和慢性抽动障碍(chronic tic, CT),共40例,TS&ADHD]和抽动障碍组[TS和CT,共82例,TS&CT]两组,采用聚合酶链反应、可变重复序列多态性分析等技术,进行抽动障碍与DRD4 exonⅢ48 bpVNTR多态性的TDT分析.结果在这一多态性位点存在5个等位基因,分别为DRD4 exonⅢ48 bp的2～6个重复等位基因.总体上没有发现抽动障碍与DRD4 exonⅢ48 bpVNTR多态性存在传递不平衡(χ2＝7.44,P＝0.12),进一步对不伴ADHD的抽动障碍组进行的TDT分析也没有发现存在这一位点的传递不平衡(χ2＝3.38,P＝0.50);而在合并ADHD的抽动障碍组中发现,合并ADHD的抽动障碍与DRD4 exonⅢ48 bpVNTR多态性在总体上存在传递不平衡(χ2＝11.74,P＝0.02),进一步对单个等位基因的TDT分析显示,合并ADHD的抽动障碍与DRD4 exonⅢ48 bp的5个重复和6个重复等位基因(长重复等位基因)存在传递不平衡(χ2＝10.57,P＝0.032,χ2＝6.13,P＝0.01).结论 DRD4 exonⅢ48 bpVNTR长重复等位基因与合并ADHD的抽动障碍存在关联,DRD4 exonⅢ48 bpVNTR长重复等位基因可能是中国人群合并ADHD的抽动障碍的遗传危险因素.     

Association study between the dopamine D4 receptor gene and schizophrenia

The dopamine D4 receptor is of major interest in schizophrenia research due to its high affinity for the atypical neuroleptic cloza-pine and a high degree of variability in the receptor gene (DRD4). Although several genetic linkage analyses performed on schizophrenia multiplex families from different regions of the world have either excluded or failed to prove that DRD4 is a major genetic factor for the development of schizophrenia, analyses for moderate predisposing effects are still of significant interest. We performed a study examining differences in allele frequencies of 4 different DRD4 polymorphisms in schizophrenia patients and age, sex, and ethnic origin matched controls. None of these 4 polymorphisms showed evidence for genetic association with schizophrenia, although a trend towards excess of the allele with 7 repeats in the (48)_n bp exon III polymorphism was observed. Complexities in the DRD4 genetic investigation and further analytic approaches are discussed. © 1995 Wiley-Liss, Inc.     

Dopamine DRD2/Cys311 is not associated with chronic schizophrenia

A mutation in the DRD2 receptor gene has been reported in association with schizophrenia in Japanese and Caucasian populations. The variation, Ser to Cys at codon 311, occurs in the third intracellular loop of the receptor and is therefore putatively functional. We report the results of screening US Caucasian schizophrenic and nonschizophrenic populations. We detected the occurrence of the DRD2 Cys311 variant in both schizophrenics and controls. Our data demonstrates no significant difference between the frequency of Cys311 in Caucasian schizophrenic and non-schizophrenic populations, indicating no association with schizophrenia. © 1996 Wiley-Liss, Inc.     

单胺氧化酶A基因多态性与精神分裂症的关联研究

目的探讨河南地区汉族人群单胺氧化酶A（monoamine oxidase A，MAOA）基因多态性与精神分裂症的关系。方法参照CCMD-3诊断标准，选取212例精神分裂症患者与168名正常对照，应用聚合酶链反应及限制性片段长度多态性技术检测MAOA基因多态性，采用病例一对照的关联分析方法对精神分裂症患者及正常对照的基因型和等位基因频率进行分析。结果（1）MAOA基因的基因型在患者组和对照组中均符合Hardy-Weinberg平衡定律（X^2=0．618，dr：2，P〉0、05；X^2=3．173，df=2，P〉0．05）。（2）MAOA基因的基因型和等位基因频率在患者组与对照组间的分布差异无统计学意义（P〉0．05）。（3）按性别分组，男性患者组中CT基因型分布频率显著高于男性对照组（X^2=7．654，P=0．022）。（4）MAOA基因的基因型和等位基因频率在家族史阴、阳性间的分布差异无统计学意义（P〉0．05）。结论没有发现MAOA基因多态性与汉族精神分裂症的发病有关联，但对性别发病有影响，基因型CT可能是男性精神分裂症发病的易感因素。     

Meta-analysis of DRD3 gene and schizophrenia: Ethnic heterogeneity and significant association in caucasians

The involvement of dopamine in the etiology of schizophrenia is suggested by a number of neurobiological and pharmacological data, the dopamine D3 receptor (DRD3) being selectively expressed in brain regions which may be specifically involved in the risk for schizophrenia. The gene coding for DRD3 has thus been extensively analyzed. Since the initial report providing substantial evidence for an association of homozygosity of either allele of the gene coding for DRD3 (BalI polymorphisms) with schizophrenia, a flurry of replicating studies has appeared, which have been split into confirmations and nonreplications in North European Caucasian, Mediterranean, Asian, American, and African populations. The involvement of DRD3 polymorphisms thus remains questionable, particularly as no linkage studies have favored a nonrandom segregation of DRD3 alleles and schizophrenia. We performed a metaanalysis from 29 independent samples, from 24 different association studies so far published, allowing the examination of 2,619 schizophrenic patients and 2,517 controls. No significant differences of genotype counts were noted between patients and controls for the whole sample, considering frequency of any genotype. Starting from the high variability of the genotypes in different geographical areas, the impact of ethnic heterogeneity was taken into account. When the studies were reorganized in five groups according to geographical origin of samples, both homozygosity and 1-1 genotype revealed significant heterogeneity (P < 0.05). We specifically found an excess of homozygosity and 1-1 genotype in schizophrenic patients only in the African and Caucasian groups (P < 0.05). The present analysis suggests a small but significant effect of DRD3 in the susceptibility to schizophrenia, at least in Caucasians. Am. J. Med. Genet. (Neuropyschiatr. Genet.) 81:318–322, 1998. © 1998 Wiley-Liss, Inc.     

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

An excess dopaminergic activity may be implicated in the etiology of schizophrenia. Our objective was to identify nucleotide variants in the 5' region of the dopamine D2 receptor gene (DRD2) and to clarify their effects on schizophrenia. We identified two polymorphisms, the A-241G and -141C Ins/Del, by examination of 259 bp in the 5'-flanking region and 249 bp of exon 1 of DRD2. Reporter constructs containing the -141C Del allele cloned into a luciferase reporter plasmid drove 21% (Y-79 cells) and 43% (293 cells) expression compared with the -141C Ins allele. In a case-control study, the -141C Del allele frequency was significantly lower in 260 schizophrenic patients than in 312 controls (OR = 0.60, 95%CI 0.44-0.81, P < 0.001). No significant association was found between the A-241G polymorphism and in vitro luciferase activity, or in allele frequency between the patients versus controls. These findings show that the -141C Ins/Del may be a functional polymorphism in the 5'-promoter region of DRD2 and may affect the susceptibility to schizophrenia.      

Dopamine receptor D4 gene is not associated with major psychoses

We previously reported an association between dopamine receptor D4 (DRD4) gene exon 1 variants and delusional disorder. The aim of this investigation was to study the DRD4 gene exon 1 and 3 variants in schizophrenia, delusional, bipolar, and unipolar disorders. We studied 651 inpatients affected by schizophrenia (n = 229), delusional (n = 86), bipolar (n = 210), and unipolar (n = 126) disorders (DSM III-R) and 471 healthy controls; these were typed for DRD4 variants at the first and third exon using polymerase chain reaction techniques. DRD4 variants were not associated with schizophrenic and delusional subjects even when possible confounders like gender and onset were considered. A marginal association between DRD4 exon 3 variants with unipolar (excess of DRD4*2/4, p = 0.004) and bipolar (excess of DRD4*2/4, p = 0.001) disorders was observed, both associations drop to insignificance when corrected for multiple testing. Our results exclude that coding variants of the DRD4 exon 1 and 3 may play a major role in conferring susceptibility to major psychoses; moreover, we could not replicate the association of DRD4 exon 1 variant with delusional disorder. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 88:486–491, 1999. © 1999 Wiley-Liss, Inc.     

A dopamine D2 receptor gene-related polymorphism is associated with schizophrenia in a Spanish population isolate

Numerous lines of evidence have highlighted the involvement of the dopamine system in the pathophysiology of schizophrenia. Association studies of dopaminergic genes such as the dopamine D2 receptor gene (DRD2), however, have produced contradictory results. To test the hypothesis that DRD2 polymorphisms are associated with schizophrenia, we investigated two DRD2-related polymorphisms (TaqI A1/A2 or rs1800497 and -141-C Ins/Del or rs1799732) in a Spanish population isolate from northern Spain consisting of 165 controls and 119 patients with schizophrenia. The TaqI A1 allele was less frequent in schizophrenic patients than in controls (P=0.002). A similar association was found for the TaqI A2/A2 genotype (P=0.0003). No association was found for the DRD2 -141-C Ins/Del polymorphism. The strong association between a potentially functional polymorphism, downstream of the DRD2 gene and schizophrenia, suggests that the direct or indirect functional effects of this polymorphism, acting on either the ANKK1 or DRD2 genes, may play a role in the pathophysiology of schizophrenia.     

Lack of association between dopamine receptor D4 variable numbers of tandem repeats gene polymorphism and smoking

Nicotine addiction, related to cigarette smoking, develops as a product of the complex interactions between social, environmental and genetic factors. Genes encoding the components of the dopaminergic system are thought to be associated with smoking. Literature data showed not only an association, but also a lack of association between variable number of tandem repeats (VNTR) polymorphism located in the third exon of dopamine D4 receptor (DRD4) gene and smoking. Repetitive sequence of DRD4 VNTR is 48 bp long and maximum 11 tandem copies were reported in humans. Presence of alleles with 6 and more repeats (i.e. long alleles) was associated with greater tendency to novelty seeking and addictive behaviors than the presence of 5 and less alleles (short alleles). The aim of this study was to determine the association between VNTR in DRD4 gene and present smoking status in ethnically homogenous Caucasian population from the Eastern European (Croatian) origin. Genotyping was done in 565 healthy subjects, 511 men and 54 women, respectively, who were subdivided into 176 smokers and 389 nonsmokers. Logistic regression analyses, adjusted for age and sex, revealed the lack of significant (p > 0.05) effect of the 4/4, 4/7 and 7/7 genotypes, or carriers of the long and short allele, or all genotypes of the DRD4 VNTR on smoking status. The results of this study failed to confirm the hypothesis that long allele of the DRD4 VNTR is associated with smoking status in Caucasian subjects.     

Reduced subcortical brain volumes in nonpsychotic siblings of schizophrenic patients: A pilot magnetic resonance imaging study

Substantial evidence suggests that nonpsychotic relatives of schizophrenia patients manifest subtle abnormalities in communication, eye movements, event-related potentials, and neuropsychological processes of attention, reasoning, and memory. We sought to determine whether adult relatives without psychosis or schizophrenia spectrum diagnoses might also have structural brain abnormalities, particularly in subcortical regions found to be impaired in patients with schizophrenia itself. Subjects were six sisters of schizophrenic patients and eleven normal female controls. Sixty contiguous 3 mm coronal, T1-weighted 3D magnetic resonance images (MRI) of the entire brain were acquired on a 1.5 Tesla magnet. Cortical and subcortical gray and white matter was segmented using a semiautomated intensity contour mapping algorithm. Volumes were adjusted for total brain volumes. Adjusted gray matter subcortical volumes were significantly smaller in relatives than in controls in total hippocampus, right amygdala, right putamen, left thalamus, and brainstem. Relatives had significantly enlarged left and total inferior lateral ventricles. These results, though preliminary, suggest that some never-psychotic relatives of schizophrenic patients have abnormal brain structure. If replicated in a larger sample including both sexes, these results would suggest that the genetic liability to schizophrenia is also expressed as structural brain abnormalities. Am. J. Med. Genet. 74:507–514, 1997. © 1997 Wiley-Liss, Inc.     

Schizophrenia and HLA: No association with PCR-SSOP typed classical loci in a large Irish familial sample

Susceptibility to autoimmunity is strongly influence by genes clustered in the MHC region, particularly class I and class II antigens. It has been proposed that there is an immune component in the aetiology of schizophrenia, and the distribution of human leukocyte antigens (HLA) in schizophrenic patients and controls has been investigated in numerous studies. Positive associations have been reported between schizophrenia and the HLA-A1, A2, A9, B5, Cw4, and DR8 and negative associations with HLA-DR4 and HLA-DQβ*0602. Small sample size, variable diagnostic methodology, unreliable laboratory and statistical procedures, and possible mismatching of cases and controls may have contributed to a lack of consistency of results to date. Therefore, in this investigation we used a large and carefully diagnosed homogeneous Irish familial schizophrenic sample compared with ethnically matched controls. All alleles were determined using polymerase chain reaction amplification followed by short specific oligoprobes. We found no evidence of association with 80 HLA alleles (some previously not examined) from 4 genes. Our data therefore do not support the involvement of these classical HLA loci in the aetiology of schizophrenia at least in these Irish families. The remaining classical HLA loci (HLA-B and HLA-C) should be typed when reliable DNA-based methods become available. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 88:422–429, 1999. © 1999 Wiley-Liss, Inc.     

Dopamine receptor D4 gene is not associated with major psychoses.

We previously reported an association between dopamine receptor D4 (DRD4) gene exon 1 variants and delusional disorder. The aim of this investigation was to study the DRD4 gene exon 1 and 3 variants in schizophrenia, delusional, bipolar, and unipolar disorders. We studied 651 inpatients affected by schizophrenia (n = 229), delusional (n = 86), bipolar (n = 210), and unipolar (n = 126) disorders (DSM III-R) and 471 healthy controls; these were typed for DRD4 variants at the first and third exon using polymerase chain reaction techniques. DRD4 variants were not associated with schizophrenic and delusional subjects even when possible confounders like gender and onset were considered. A marginal association between DRD4 exon 3 variants with unipolar (excess of DRD4*2/4, p = 0.004) and bipolar (excess of DRD4*2/4, p = 0.001) disorders was observed, both associations drop to insignificance when corrected for multiple testing. Our results exclude that coding variants of the DRD4 exon 1 and 3 may play a major role in conferring susceptibility to major psychoses; moreover, we could not replicate the association of DRD4 exon 1 variant with delusional disorder.     

Trend for an association between schizophrenia and D3S1310, a marker in proximity to the dopamine D3 receptor gene

There is considerable controversy regarding a putative association between schizophrenia and a biallelic BalI polymorphism in the first exon of the dopamine D3 receptor gene (DRD3), although meta-analyses of published data suggest an association. If such an association exists, it may be detectable at markers physically close to DRD3. Accordingly, we conducted a case-control association study using D3S1310, a short tandem repeat polymorphism located approximately 700 kb telomeric to DRD3 on chromosome 3q13.3. The subjects were Swedish patients with schizophrenia (DSM III-R criteria, n = 110) and screened adult controls (n = 83). A trend for a negative association with the 141 bp allele was detected (χ² = 7.6, d.f. = 1, P = 0.006; odds ratio 0.46, 95% confidence intervals 0.26, 0.81). However, following corrections for multiple comparisons using subgroups (n = 15) the difference was not significant. Also, due to the risk for population stratification in case-control association studies the results must be treated as tentative. If replicated the results may lend further support for the proposition of an association between schizophrenia and DRD3 or a gene in close proximity to DRD3 on chromosome 3q. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 88:352–357, 1999. © 1999 Wiley-Liss, Inc.     

Association analysis of polymorphisms in the upstream region of the human dopamine D4 receptor gene (DRD4) with schizophrenia and personality traits

The human dopamine D4 receptor (DRD4) is of major interest in molecular studies of schizophrenia and personality traits. We examined the association of schizophrenia and polymorphisms in the upstream region of the DRD4 gene (−768G>A in the negative modulator region; −521C>T, −376C>T, and −291C>T in the cell type-specific promoter region; and −616C>G between the two regions) in 208 schizophrenic patients and 210 normal controls. No significant difference in genotype and allele frequencies was observed between the two groups, indicating that these polymorphisms do not make a major contribution to the pathogenesis of schizophrenia. We also studied the association of polymorphisms in the upstream region and a 48-bp repeat polymorphism in exon III of the DRD4 gene with personality traits in 173 Japanese individuals who completed the temperament and character inventory (TCI). The −768G>A polymorphism was significantly associated with reward dependence (P = 0.044), while no significant association was observed between novelty seeking and polymorphisms in the upstream region or the exon III repeat polymorphism of the DRD4 gene. Received: August 28, 2000 / Accepted: October 25, 2000