A search for association between schizophrenia and dopamine-related alleles

A meta-analysis of data associating DRD4 gene polymorphisms with schizophrenia

To explore the association between DRD4 polymorphisms and schizophrenia risk, a meta-analysis was carried out with 41 case-control articles. Specifically, we included 28 articles (5,735 cases and 5,278 controls) that pertained to the 48 bp variable number tandem repeat (VNTR) polymorphism, nine articles (1,517 cases and 1,746 controls) that corresponded to the 12 bp tandem repeat (TR), six articles (1,912 cases and 1,836 controls) that addressed the 120 bp TR, 10 articles (2,927 cases and 2,938 controls) that entailed the -521 C>T polymorphism, six articles (1,735 cases and 1,724 controls) that pertained to the -616 C>G polymorphism, and four articles (1,191 cases and 1,215 controls) that involved the -376 C>T polymorphism. Pooled analysis, subgroup analysis, and sensitivity analysis were performed, and the data were visualized by means of forest and funnel plots. Results of pooled analysis indicated that the -521 CC variant (Pz=0.009, odds ratio [OR] =1.218, 95% confidence interval [CI] =1.050-1.413) and genotype L/L (ie, long allele) of the 120 bp TR were risk factors of schizophrenia (Pz=0.004, OR =1.275, 95% CI =1.081-1.504). The 48 bp VNTR, the 12 bp TR, the -616 C>G polymorphism, and the -376 C>T polymorphism were not associated with schizophrenia. Additional research is warranted to explore the association between polymorphisms of DRD4 and schizophrenia risk.

The association of insertions/deletions (INDELs) and variable number tandem repeats (VNTRs) with obesity and its related traits and complications

BACKGROUND

Despite the fact that insertions/deletions (INDELs) are the second most common type of genetic variations and variable number tandem repeats (VNTRs) represent a large portion of the human genome, they have received far less attention than single nucleotide polymorphisms (SNPs) and larger forms of structural variation like copy number variations (CNVs), especially in genome-wide association studies (GWAS) of complex diseases like polygenic obesity. This is exemplified by the vast amount of review papers on the role of SNPs and CNVs in obesity, its related traits (like anthropometric measurements, biochemical variables, and eating behavior), and its related complications (like hypertension, hypertriglyceridemia, hypercholesterolemia, and insulin resistance-collectively known as metabolic syndrome). Hence, this paper reviews the types of INDELs and VNTRs that have been studied for association with obesity and its related traits and complications. These INDELs and VNTRs could be found in the obesity loci or genes from the earliest GWAS and candidate gene association studies, like FTO, genes in the leptin-proopiomelanocortin pathway, and UCP2/3. Given the important role of the brain serotonergic and dopaminergic reward system in obesity susceptibility, the association of INDELs and VNTRs in these neurotransmitters' metabolism and transport genes with obesity is also reviewed. Next, the role of INS VNTR in obesity and its related traits is questionable, since recent large-scale studies failed to replicate the earlier positive associations. As obesity results in chronic low-grade inflammation of the adipose tissue, the proinflammatory cytokine gene IL1RA and anti-inflammatory cytokine gene IL4 have VNTRs that are implicated in obesity. A systemic proinflammatory state in combination with activation of the renin-angiotensin system and decreased nitric oxide bioavailability as found in obesity leads to endothelial dysfunction. This explains why VNTR and INDEL in eNOS and ACE, respectively, could be predisposing factors of obesity. Finally, two novel genes, DOCK5 and PER3, which are involved in the regulation of the Akt/MAPK pathway and circadian rhythm, respectively, have VNTRs and INDEL that might be associated with obesity.

SHORT CONCLUSION

In conclusion, INDELs and VNTRs could have important functional consequences in the pathophysiology of obesity, and research on them should be continued to facilitate obesity prediction, prevention, and treatment.

Associations between dopamine D2 receptor gene polymorphisms and schizophrenia risk: a PRISMA compliant meta-analysis

OBJECTIVE

To determine the relationships between dopamine D2 receptor gene polymorphisms and the risk of schizophrenia using meta-analysis.

METHOD

The PubMed, Embase, and China National Knowledge Infrastructure databases were searched to identify relevant literature published up to February 2016. The allele contrast model was used. Stata software was used for statistical analysis, with odds ratios (ORs) and 95% confidence intervals (CIs) calculated to evaluate the associations between dopamine D2 receptor gene polymorphisms and the risk of schizophrenia. Meta-regression and publication bias, trim-and-fill, subgroup, sensitivity, cumulative, and fail-safe number analyses were also performed.

RESULTS

This meta-analysis included 81 studies. The rs1801028 and rs1799732 were associated with schizophrenia risk among Asians (P=0.04, OR =1.25, 95% CI =1.01-1.55; P<0.01, OR =0.76, 95% CI =0.63-0.92, respectively), while the rs6277 was associated with schizophrenia risk in Caucasians (P<0.01, OR=0.72, 95% CI =0.66-0.79). The rs1800497 was also associated with schizophrenia risk in population-based controls (P<0.01, OR =0.84, 95% CI =0.72-0.97). The rs6275, rs1079597, and rs1800498 were not associated with schizophrenia risk. In addition, meta-regression indicated that the controls may be sources of heterogeneity for the rs1801028 single-nucleotide polymorphism (SNP), while ethnicity may be sources of heterogeneity for the rs6277 SNP. Publication bias was significant for the rs1801028 SNP, and this result changed after the publication bias was adjusted using the trim-and-fill method.

CONCLUSION

This meta-analysis demonstrated that the rs1801028 may be a risk factor for susceptibility to schizophrenia among Asians, while the rs1799732 may be a protective factor for that population. Large-sample studies are necessary to verify the results of this meta-analysis.

The -141C Ins/Del and Taq1A polymorphism in the dopamine D2 receptor gene may confer susceptibility to schizophrenia in Asian populations

It has been reported that two single nucleotide polymorphisms (SNP) Taq1A and -141C Ins/Del in the DRD2 gene may be associated with susceptibility to schizophrenia. Due to inconclusive and mixed results, a meta-analysis was conducted to further clarify the relationship between the two SNP and schizophrenia susceptibility. A systematic literature search for the association of these two SNP with schizophrenia susceptibility was conducted using PubMed, ScienceDirect, Chinese Biomedical Literature Database, and Chinese National Knowledge Infrastructure. Odds ratios (OR) with 95% confidence intervals (CI) were used to assess the strength of the associations reported. A total of 5558 schizophrenic patients and 6792 healthy controls from 31 articles were included in this study. Evidence regarding the association between -141C Ins/Del polymorphism and schizophrenia was found in the allele frequency comparison (Ins versus Del: OR 1.29, 95% CI 1.06-1.57; p=0.01, Praw=0.1, PFalse Discovery Rate=0.023). In ethnic subgroup analysis, the result revealed that the 141C Ins/Del polymorphism was associated with schizophrenia in all genetic models in Asians, but not in Caucasians. For Taq1A polymorphism, a significant association was found in the allele frequency (A1 versus A2: OR 0.71, 95% CI 0.52-0.98, p=0.03). Stratification by ethnicity indicated an association between the Taq1A polymorphism and schizophrenia in Asians, but not Caucasians. The present study suggests that the -141C Ins/Del polymorphism carries a significantly increased risk of schizophrenia, while the Taq1A polymorphism carries a significantly decreased risk of schizophrenia susceptibility in Asians.

Association between DRD2 (rs1799732 and rs1801028) and ANKK1 (rs1800497) polymorphisms and schizophrenia: a meta-analysis

The role of dopamine D2 receptor (DRD2) polymorphisms in schizophrenia remains controversial. We performed a meta-analysis to determine whether DRD2 polymorphisms influence the risk of schizophrenia and examined the relationship between rs1799732, rs1801028, and rs1800rs028 an23381d rs1800497 genetic variants and the etiology of schizophrenia. Relevant case-control studies were retrieved by database searches and selected according to established inclusion criteria. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated to evaluate the strength of the associations. Meta-regression, subgroup analysis, sensitivity analysis, and cumulative meta-analysis were performed. A total of 76 studies with 16096 cases and 18965 controls were included. Specifically, 24 studies with 6075 cases and 6643 controls involved rs1799732, 36 studies with 8043 cases and 10194 controls involved rs1801028 and 16 studies with 1978 cases and 2128 controls involved rs1800497. No significant associations were observed between rs1799732 and rs1800rs732 and rs1800497 and schizophrenia. The rs1801028 locus was associated with schizophrenia, with a pooled OR of 1.221 (95% CI = 1.037-1.438, P = 0.016). This meta-analysis indicates that the rs1801028 locus may be associated with schizophrenia. These data provide possible references for future case-control studies related to schizophrenia.

Identification of ANKK1 rs1800497 variant in schizophrenia: new data and meta-analysis

One functional polymorphism (rs1800497) within the ankyrin repeat and kinase domain containing-1 gene (ANKK1) was reported to be associated with schizophrenia, but results among different studies vary and conclusions remain controversial. The present study sought to clarify this potential association among a population of Han Chinese with early onset schizophrenia using a case-control (396 patients and 399 controls) and family based study (103 trios). We then performed a meta-analysis (comprising 11 case-control and 2 family-based studies) based on the present literature. Results of the association study revealed no significant difference in allele and genotype frequencies between the cases and controls, and no significant transmission distortion was detected. Kaplan-Meier survival analysis showed that age at onset in schizophrenia was significantly associated with the rs1800497 polymorphism in female patients, but not in males. Female T allele carriers had a lower age at onset than those without T allele (log rank statistic χ(2) = 5.16, P = 0.023; corrected P = 0.046). Meta-analysis results indicated that rs1800497 is not associated with schizophrenia in the overall population (P = 0.77 for the case-control studies; P = 0.06 for the family-based studies). Our results support the hypothesis that rs1800497 polymorphism is likely to have a modifying rather than causative effect on schizophrenia. These findings may represent a significant genetic clue for the etiology of schizophrenia in females, but further investigation is required to clarify the exact role of ANKK1 in the development of schizophrenia.

Functional polymorphism (C-824T) of the tyrosine hydroxylase gene affects IQ in schizophrenia

AIMS

Progressive cognitive decline has been an important issue in the treatment and care of patients with schizophrenia. Tyrosine hydroxylase (TH) is the rate-limiting enzyme for the biosynthesis of catecholamine, including dopamine and noradrenaline. In this report, we examined a possible association of a genetic variant in the TH promoter region.

METHODS

Association of a genetic variant in the TH promoter region, C-824T (rs10770141), with intellectual ability in 132 patients with schizophrenia and 282 healthy subjects was examined. The transcriptional activity of the plasmids harboring the TH promoter region with either C or T nucleotide at -824 was assayed using a luciferase gene as a reporter.

RESULTS

We found significant effects of the genotype on the full-scale IQ, verbal IQ, and performance IQ, in patients with schizophrenia. IQ was lower in individuals with the C/C genotype than those with T carriers. The plasmid with the T allele at -824 showed higher transcriptional activity than that with the C allele in a transient transfection experiment using a luciferase gene as a reporter, implying that the T carriers may have higher TH activities and retain higher levels of catecholamines in the brain.

CONCLUSIONS

The present data suggest that the biosynthesis of catecholamine by the action of TH should be deeply involved in decreased intellectual ability in patients with schizophrenia. This is the first report, as far as we know, showing a correlation between TH expression and IQ in humans.

DRD4 VNTR polymorphism and age at onset of severe mental illnesses

A large number of studies has investigated the hypothesis that DRD4 48 bp variable number of tandem repeat (VNTR) polymorphism is involved in the etiology of schizophrenia and bipolar disorder. However, the results are inconsistent likely due to genetic and phenotypic heterogeneity. Age at onset (AAO) is considered an important alternate phenotype for genetic investigations of psychiatric disorders. In the present study, the DRD4 VNTR 7 repeat allele (7R) was examined in 477 patients with major psychoses. Age at onset was defined as the age of first psychotic episode for schizophrenia and the age at appearance of first clinically recognized symptoms for the bipolar sample. Our results showed an interaction between sex and DRD4 genotypes among schizophrenia patients (n=203, β=.213, p=.017). On comparing AAO between carriers and non-carriers of the 7R, we observed that females with 7R present had later onset (p=.021). The effect was not observed for males. In the sample with bipolar disorder, we observed significant association between DRD4 7R-genotype and AAO (n=274, β=-.148, p=.012). No interaction was observed between sex and genotypic groups of the bipolar sample. The 7R was associated with early onset of the bipolar illness (p=.028). In summary, our results suggest that the 7R is associated with AAO in both schizophrenia and bipolar disorders. The effect was observed across both sexes in bipolar disorder, but specifically in females for schizophrenia.

Dopamine pathology in schizophrenia: analysis of total and phosphorylated tyrosine hydroxylase in the substantia nigra

INTRODUCTION

Despite the importance of dopamine neurotransmission in schizophrenia, very few studies have addressed anomalies in the mesencephalic dopaminergic neurons of the substantia nigra/ventral tegmental area (SN/VTA). Tyrosine hydroxylase (TH) is the rate-limiting enzyme for the production of dopamine, and a possible contributor to the anomalies in the dopaminergic neurotransmission observed in schizophrenia.

OBJECTIVES

In this study, we had three objectives: (1) Compare TH expression (mRNA and protein) in the SN/VTA of schizophrenia and control postmortem samples. (2) Assess the effect of antipsychotic medications on the expression of TH in the SN/VTA. (3) Examine possible regional differences in TH expression anomalies within the SN/VTA.

METHODS

To achieve these objectives three independent studies were conducted: (1) A pilot study to compare TH mRNA and TH protein levels in the SN/VTA of postmortem samples from schizophrenia and controls. (2) A chronic treatment study was performed in rodents to assess the effect of antipsychotic medications in TH protein levels in the SN/VTA. (3) A second postmortem study was performed to assess TH and phosphorylated TH protein levels in two types of samples: schizophrenia and control samples containing the entire rostro-caudal extent of the SN/VTA, and schizophrenia and control samples containing only mid-caudal regions of the SN/VTA.

RESULTS AND CONCLUSION

Our studies showed impairment in the dopaminergic system in schizophrenia that could be mainly (or exclusively) located in the rostral region of the SN/VTA. Our studies also showed that TH protein levels were significantly abnormal in schizophrenia, while mRNA expression levels were not affected, indicating that TH pathology in this region may occur posttranscriptionally. Lastly, our antipsychotic animal treatment study showed that TH protein levels were not significantly affected by antipsychotic treatment, indicating that these anomalies are an intrinsic pathology rather than a treatment effect.

The dopamine D4 receptor: biochemical and signalling properties

Dopamine is an important neurotransmitter that regulates several key functions in the brain, such as motor output, motivation and reward, learning and memory, and endocrine regulation. Dopamine does not mediate fast synaptic transmission, but rather modulates it by triggering slow-acting effects through the activation of dopamine receptors, which belong to the G-protein-coupled receptor superfamily. Besides activating different effectors through G-protein coupling, dopamine receptors also signal through interaction with a variety of proteins, collectively termed dopamine receptor-interacting proteins. We focus on the dopamine D4 receptor, which contains an important polymorphism in its third intracellular loop. This polymorphism has been the subject of numerous studies investigating links with several brain disorders, such as attention-deficit hyperactivity disorder and schizophrenia. We provide an overview of the structure, signalling properties and regulation of dopamine D4 receptors, and briefly discuss their physiological and pathophysiological role in the brain.

Variable number of tandem repeat polymorphisms of DRD4: re-evaluation of selection hypothesis and analysis of association with schizophrenia

Associations have been reported between the variable number of tandem repeat (VNTR) polymorphisms in the exon 3 of dopamine D4 receptor gene gene and multiple psychiatric illnesses/traits. We examined the distribution of VNTR alleles of different length in a Japanese cohort and found that, as reported earlier, the size of allele '7R' was much rarer (0.5%) in Japanese than in Caucasian populations (approximately 20%). This presents a challenge to an earlier proposed hypothesis that positive selection favoring the allele 7R has contributed to its high frequency. To further address the issue of selection, we carried out sequencing of the VNTR region not only from human but also from chimpanzee samples, and made inference on the ancestral repeat motif and haplotype by use of a phylogenetic analysis program. The most common 4R variant was considered to be the ancestral haplotype as earlier proposed. However, in a gene tree of VNTR constructed on the basis of this inferred ancestral haplotype, the allele 7R had five descendent haplotypes in relatively long lineage, where genetic drift can have major influence. We also tested this length polymorphism for association with schizophrenia, studying two Japanese sample sets (one with 570 cases and 570 controls, and the other with 124 pedigrees). No evidence of association between the allele 7R and schizophrenia was found in any of the two data sets. Collectively, this study suggests that the VNTR variation does not have an effect large enough to cause either selection or a detectable association with schizophrenia in a study of samples of moderate size.

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.

Association and synergistic interaction between promoter variants of the DRD4 gene in Japanese schizophrenics

Recent association studies suggest that polymorphisms in the promoter and exon 1 upstream region of the dopamine D4 receptor (DRD4) gene play a functional role in the development of common psychiatric illnesses, although there are also conflicting results. In this study, we re-sequenced this region to identify all genomic variants, and tested them for association with schizophrenia. A total of 570 Japanese schizophrenic cases with matched controls were studied by genotyping all identified/validated common polymorphisms (−1106T>C, −906T>C, −809G>A, −616G>C, −521T>C, −376C>T, −291C>T and 12-bp repeat) and a known microsatellite (120-bp tandem duplication) in the upstream region. A single nucleotide polymorphism (SNP) −809G>A in the promoter region was found to be significantly associated with disease (P=0.018 and 0.032 for allelic and genotypic comparisons, respectively), although not surviving after Bonferroni correction. Logistic regression analysis showed that a combination of the four polymorphisms, −809G>A, −616G>C, −291C>T and the 12-bp repeat, conferred a susceptibility to schizophrenia. These results suggest that the upstream variants have a primary functional effect in the etiology of schizophrenia in the Japanese population.

Meta-analysis shows association between the tryptophan hydroxylase (TPH) gene and schizophrenia

A number of studies have suggested an association between schizophrenia and the tryptophan hydroxylase (TPH) and tyrosine hydroxylase (TH) genes. On the other hand, several studies attempting to replicate these findings have produced mixed results, possibly reflecting inadequate statistical power of the individual studies as well as the heterogeneity inherent in schizophrenia. In an attempt to clarify this inconsistency our meta-analysis has combined all the studies using multiple research methods published up to February 2006 to give a comprehensive picture of the role of three hydroxylase-related genes. The TPH A218C/A779C (OR = 1.18, 95% C.I. 1.06-1.33, P = 0.004) revealed a significant association with schizophrenia. However, the evidence for the TH and phenylalanine hydroxylase (PAH) genes was weak. No publication bias was detected in current studies. The findings, which may implicate the involvement of TPH in the pathogenesis of schizophrenia, have potentially important clinical, scientific and public health implications as well as providing a putative basis for the study of hydroxylase-related drugs. To our knowledge, this is the first meta-analysis of association between the three genes and schizophrenia.

Schizophrenia is not associated with DRD4 48-base-pair-repeat length or individual alleles: results of a meta-analysis

BACKGROUND

The gene DRD4, coding for dopamine receptor D4, was considered a candidate for association with schizophrenia based on its upregulation in postmortem schizophrenic brain and affinity for clozapine. Many studies sought allelic association of a 48-base-pair repeat in DRD4 exon 3 with schizophrenia, but found no strong evidence for a relationship. The present work sought to determine if this observation reflected the true absence of association or the low power of individual studies.

METHODS

We performed four meta-analyses, sequentially considering the two-, four-, and seven-repeat alleles as risk alleles, and then considering repeat length of the 48-base-pair segment as a risk factor. Each meta-analysis included at least 2,300 cases and 2,100 controls from 14-16 studies.

RESULTS

The pooled odds ratio from each analysis approximated 1.0, and none were significant. Heterogeneity was not observed, although gender moderated the effects of repeat length and the seven-repeat allele.

CONCLUSIONS

Despite over 90% power to detect a significant odds ratio of 1.4 or less, none was observed. This polymorphism seems not to influence risk for most schizophrenia cases; however, a sex-dependent relationship, or a role in some clinical features of the disorder, cannot be excluded and should be pursued experimentally.

Family-based association study of 5-HTTLPR, TPH, MAO-A, and DRD4 polymorphisms in mood disorders

Variants of the functional polymorphism in the serotonin transporter (upstream regulatory region: 5-HTTLPR), the tryptophan hydroxylase (TPH), the monoamine oxidase A (MAO-A), and the dopamine receptor D4 (DRD4) genes have all been associated with mood disorders. The aim of this study was to test those hypotheses by using a family-based association approach. Both diagnoses and psychopathology were used for phenotype definitions. A total of 134 nuclear families with mood disorders, with probands affected by bipolar (n = 103) or major depressive (n = 58) disorders, were included in the study. All subjects were typed for the above-mentioned gene variants using polymerase chain reaction (PCR) technique. No significant transmission disequilibrium was found in the overall sample for any polymorphism. A separate analysis of bipolar subjects only, or the use of continuous psychopathologic traits as affectation status did not influence the observed results. Our study did not support the involvement of 5-HTTLPR, TPH, MAO-A, or DRD4 polymorphisms in mood disorders.

DRD4 exon 3 variants associated with delusional symptomatology in major psychoses: a study on 2,011 affected subjects

We previously reported an association of DRD4 exon3 long allele variants with delusional symptomatology independently from diagnoses. The aim of this investigation was to study DRD4 in major psychoses and to test the association in a larger sample. We studied 2,011 inpatients affected by bipolar disorder (n = 811), major depressive disorder (n = 635), schizophrenia (n = 419), delusional disorder (n = 104), psychotic disorder not otherwise specified (n = 42), and 601 healthy controls. A subsample of 1,264 patients were evaluated using the OPCRIT checklist and differences of symptomatology factor scores among genetic variants were assessed using one-way analysis of variance (ANOVA). DRD4 allele and genotype frequencies in bipolars, schizophrenics, delusionals, and psychotic NOS were not significantly different from controls; major depressives showed a trend toward an excess of DRD4*Short and DRD4*Short/Short variants versus controls. The ANOVA on factor scores in the whole subsample of 1,264 subjects showed a significant difference on delusion factor in allele analysis (P = 0.007), and in genotype one (P = 0.018), with DRD4*Long containing variants associated with severe symptomatology. The analysis in the replication subjects only (n = 803) showed a trend in the same direction, though not reaching the significance level. This analysis in an enlarged sample suggests that DRD4*Long alleles exert a small but significant influence on the delusional symptomatology in subjects affected by major psychoses.

No association between a promoter dopamine D(4) receptor gene variant and schizophrenia

The dopamine D(4) receptor has been implicated in the pathogenesis of schizophrenia. An association between a putative functional promoter polymorphism (-521C/T) in the dopamine D(4) receptor gene (DRD4) and schizophrenia was recently reported. In the present study, patients with schizophrenia (n = 132) and control subjects (n = 388) were analyzed with respect to the DRD4 - 521C/T polymorphism. No significant case control differences emerged. The present results do not support a major role for DRD4 in the etiology of schizophrenia among Caucasians from Sweden.

Association and excess of transmission of a DRD2 haplotype in a sample of French schizophrenic patients

The gene which codes for dopamine receptor D2 (DRD2) is considered as one of the most relevant candidate genes in schizophrenia. Previous genetic studies focusing on this gene gave conflicting results, potentially because of the differences in methodology (linkage versus association studies), and the different loci analyzed (the DRD2 gene having many polymorphisms). We used a progressive strategy with three different approaches (case/control, haplotype relative risk and transmission disequilibrium test) and investigated two genetic polymorphisms (TaqI B1/B2 and TaqI A1/A2, spanning the coding region of the DRD2 gene) in 50 patients with DSM-IV diagnoses of schizophrenia, in their 100 parents and in 50 healthy, matched controls. Firstly, we found a significant excess of the two alleles (B2 and A2) in the schizophrenic group compared to unaffected controls. Secondly, we found an excess of transmission from the parents to their affected children, using the haplotype relative risk design applied to the B2A2 haplotype. Finally, the transmission disequilibrium test showed evidence for linkage between B2A2 haplotype and schizophrenia. The significant excess of the B2A2 haplotype in schizophrenic patients is specifically observed in a subsample of patients with a disease onset occurring after 20 years of age. As the haplotype contains nearly the entire DRD2 gene, we found convergent evidence in our sample for a significant role of the DRD2 gene in the risk for schizophrenia. This haplotype may be more specifically involved in the disorder's onset at a later age in some patients, or, alternatively, may be implicated as a modifying factor acting on age of onset.

Dopamine D4 receptor (DRD4) gene polymorphism in the first psychotic episode

BACKGROUND

Dopamine D4 receptor (DRD4) has shown some interesting properties at genetic and possibly functional levels. It has been suggested that some molecular variants of the DRD4 gene (e.g., four and seven alleles) could be implicated in the pathogenesis of psychotic disorders. Additionally, the VNTR polymorphism could be implicated in part of the response to treatment with neuroleptics. This study tested the possible association between the 48-bp tandem repeats in exon 3 of the DRD4 gene and patients experiencing their first psychotic episode.

METHODS

Patients with a first psychotic episode (FPE, n = 37) were diagnosed and compared with a matched control group (n = 37). The FPE group was subdivided into two categories: those with nonaffective and those with affective psychoses. The variable number of tandem repeats (VNTR) region of the DRD4 gene was amplified by PCR procedures. Chi-square statistics and appropriate corrections and adjustments were used for data analysis.

CONCLUSIONS

A significantly lower frequency of the four repeat (4-R) carriers in the FPE group was observed. This association was sustained mainly by the affective psychotic group (chi2 = 9.99 df = 2, p = 0.0073). Although these results require testing with stringent methods, it is suggested that the DRD4-4R allele may confer some protection against psychosis, mainly of the affective subtype.

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.

Search for the influence of the tyrosine hydroxylase (TCAT)(n) repeat polymorphism on personality traits

A putatively functional tetranucleotide repeat polymorphism in the tyrosine hydroxylase gene (TH) has been investigated with regard to different aspects of psychopathology. We investigated whether reported associations of this TH polymorphism may reflect associations with common personality traits. Personality was assessed by the NEO Personality Inventory-Revised version (NEO PI-R), in 205 healthy Caucasian volunteers. Tendencies for higher scores in the neuroticism (N) facets, Angry hostility (P=0.008) and Vulnerability (P=0.021), were observed among carriers of one of the alleles (T8). Healthy women with the T6/T10 genotype had significantly higher scores (P=0.001) in the Deliberation and Dutifulness facets (P=0.031) (the Conscientiousness dimension, C) and lower scores (P=0.031) in the Feelings facet (the Openness dimension, O). We concluded that: (1) higher mean scores in the Neuroticism facets among T8 allele carriers are consistent with previous data and warrants further research; (2) the T6/T10 genotype may influence personality among women; (3) these data should be cautiously interpreted in the absence of corroborating data.

Dopamine D4 receptors

Initial investigations on dopamine D4 receptors generated much interest in the role of this receptor in schizophrenia and other aspects of human behavior, as well as new opportunities for novel therapeutics. However, attempts to treat patients suffering from schizophrenia with dopamine D4 agents have failed to yield satisfactory results so far. An examination of the dopamine D4 literature shows that contrasting and conflicting data seemed to be the norm in this field of research. This paper reviews the literature on the dopamine D4 receptor and discusses many of the associated methodological problems that might have contributed to the paradoxical findings.

Dopamine receptor D4 is not associated with antidepressant activity of sleep deprivation

Total sleep deprivation (TSD) is an effective treatment for mood disorders which is thought to act through an enhancement in several neurotransmitter pathways including dopaminergic transmission. However, not all patients respond to TSD and genetic factors are likely to play a major role in determining TSD response. The aim of this study is to investigate the influence of dopamine receptor D4 exon 3 (DRD4) variants on TSD antidepressant efficacy in bipolar disorder. One hundred and twenty-four depressed inpatients affected by bipolar disorder (DSM-IV) were treated with repeated cycles of TSD and were typed for DRD4 variants at the third exon using polymerase chain reaction (PCR) techniques. DRD4 variants were not associated with TSD outcome. Consideration of possible stratification effects such as gender, age at onset and duration of illness did not reveal any association either. DRD4 exon 3 variants are not a main factor influencing TSD outcome in bipolar disorder.

Association between a promoter polymorphism in the dopamine D2 receptor gene and schizophrenia

Genetic factors and dopamine receptor dysfunction have been implicated in the pathophysiology of schizophrenia. Recently, an association between a putative functional promoter polymorphism (-141C Ins/Del) in the dopamine D2 receptor gene and schizophrenia was reported. We investigated unrelated Swedish schizophrenic patients (n = 129) and control subjects (n = 179) for the same polymorphism. Similarly to a previous Japanese report, the - 141C Del allele frequency was significantly lower in patients than controls (chi2=4.4, 1 df, p<0.05; odds ratio 0.49, 95% confidence interval 0.26-0.91). The present and previous results may indicate that the -141C Ins/Del dopamine D2 receptor gene polymorphism affects susceptibility to schizophrenia.

Genetic antecedents of dopamine dysfunction in schizophrenia

BACKGROUND

Relatives of schizophrenic probands frequently manifest attenuated features of this illness including the negative symptoms and the milder positive psychotic symptoms. These two symptom dimensions are hypothesized to be associated with decreased and increased brain dopamine (DA) functions, respectively, raising the possibility that DA abnormalities may be present in the relatives of schizophrenic probands.

METHODS

Plasma homovanillic acid (HVA), the major DA metabolite and an indicator of brain DA activity, was measured in nonpsychotic, physically healthy first-degree relatives (n = 55) of schizophrenic probands and in normal subjects (n = 20) without a family history of schizophrenia.

RESULTS

Plasma HVA inversely correlated with negative symptoms and positively correlated with attenuated positive symptoms. Also, relatives had decreased plasma HVA compared to normal subjects, consistent with the fact that these relatives are characterized by negative symptoms. These findings were not related to major peripheral factors that could affect plasma HVA suggesting that the findings may reflect changes in brain DA activity.

CONCLUSIONS

Negative symptoms indicating a genetic diathesis to schizophrenia in relatives may have a biologic basis in reduced DA activity and the DA dysfunction of schizophrenia may have genetic antecedents. This opens an important new avenue for further study of DA in this illness.

The CCK-A receptor gene possibly associated with auditory hallucinations in schizophrenia

In this study, a PstI polymorphic site with two individual alleles, namely A1 and A2, was identified withinthe boundary between intron 1 and exon 2 of the cholecystokinin (CCK) type A receptor gene. The PstI polymorphic site was used as a genetic marker to study its association with psychotic symptoms in schizophrenia. A significant difference in allelic frequency was found between schizophrenic patients with and without auditory hallucinations(chi(2) = 6.26, df = 1, P = 0.012), and the odds ratio for the allelic association was 2.21 (95% CI 1.18-4.15) with an attributable fraction of 0.1. The frequency of A1-A1 and A1-A2 genotypes showed a significant excess in schizophrenic patients with auditory hallucinations as compared to those without such symptoms (chi(2) = 5.45, df = 1, P = 0.02), and the odds ratio for the genotypic association was 2.27 (95% CI 1. 13-4.57) with an attributable fraction of 0.177. The haplotype-based haplotype relative risk (HHRR) test revealed a significant difference between transmitted and non-transmitted alleles in nuclear families of schizophrenic patients with auditory hallucinations (chi(2) = 4.54, df = 1,P = 0.033) but not in those of schizophrenic patients without them. The present study suggests that the CCK-A receptor gene may be associated with auditory hallucinations in schizophrenia.

Possible association of catecholamine turnover with the polymorphic (TCAT)n repeat in the first intron of the human tyrosine hydroxylase gene

Five allelic fragments were typed by a PCR-based process with a pair of primers specific for the polymorphic sequence due to (TCAT)n tetranucleotide repeat, a microsatellite repeat, in the first intron of the human tyrosine hydroxylase gene, i.e. A1, A2, A3, A4 and A5. Comparisons of some neurochemical parameters of the catecholamine pathway were then made between the unrelated individuals genotypically classified into six subgroups, five homozygotic and one heterozygotic. Among the six subgroups, the individuals with the A2/A2 genotype had the highest levels of serum noradrenaline and those with the A4/A4 genotype had the lowest, and the individuals with the A1/A1 genotype had the highest levels of serum homovanillic acid. These findings suggest that polymorphism of the (TCAT)n repeat in the first intron of the human tyrosine hydroxylase gene may be associated with catecholamine turnover. Possibly, the two alleles, A2 and A4, may be related to the high and low excitabilities of the noradrenergic nerves, respectively, and the allele, A1, may be associated with the up-regulation of dopamine turnover.

Tyrosine hydroxylase allelic distribution in suicide attempters

A tetranucleotide repeat polymorphism in the first intron of the tyrosine hydroxylase (TH) locus was examined in a group of 118 adult suicide attempters and 78 control subjects. The suicide attempters were diagnosed according to DSM-III-R criteria at the index attempt and represented the following diagnoses: major depression (18), dysthymia (13), anxiety disorders (16), adjustment disorders (29), psychoactive substance abuse disorders (27) and psychotic disorders (15). A significant variation in the prevalence of carriers of the TH-K3 allele (high for suicide attempters with adjustment disorders, P = 0.0023) and a tendency toward a variation of the TH-K1 allele (low among all suicide attempters, P = 0.046) was observed. In light of other data the variation of TH-K1 and TH-K3 suggests that these alleles may reflect predisposition for a common phenotype with altered vulnerability for psychiatric disorders.