Childhood/early adolescence-onset and adult-onset schizophrenia. Heterogeneity at the dopamine D3 receptor gene

No association between dopamine D3 receptor gene Ser9Gly polymorphism (rs6280) and risk of schizophrenia: an updated meta-analysis

OBJECTIVE

Ser9Gly (rs6280) is a functional single-nucleotide polymorphism (SNP) in the dopamine receptor D3 (DRD3) gene that may be associated with schizophrenia. We performed a meta-analysis to determine whether Ser9Gly influences the risk of schizophrenia and examined the relationship between the Ser9Gly SNP and the etiology of schizophrenia.

METHODS

Case-control studies were retrieved from literature databases in accordance with established inclusion criteria. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated to evaluate the strength of the association between Ser9Gly and schizophrenia. Subgroup analysis and sensitivity analysis were also performed.

RESULTS

Seventy-three studies comprising 10,634 patients with schizophrenia (cases) and 11,258 controls were included in this meta-analysis. Summary results indicated no association between Ser9Gly and risk of schizophrenia. In the dominant genetic model, the pooled OR using a random effects model was 0.950 (95% CI, 0.847-1.064; P=0.374).

CONCLUSION

Results of this meta-analysis suggest that the Ser9Gly SNP is not associated with schizophrenia. These data provide possible avenues for future case-control studies related to schizophrenia.

The effects of olanzapine on genome-wide DNA methylation in the hippocampus and cerebellum

Background

The mechanism of action of olanzapine in treating schizophrenia is not clear. This research reports the effects of a therapeutic equivalent treatment of olanzapine on DNA methylation in a rat model in vivo.

Genome-wide DNA methylation was assessed using a MeDIP-chip analysis. All methylated DNA immunoprecipitation (MeDIP), sample labelling, hybridization and processing were performed by Arraystar Inc (Rockville, MD, USA). The identified gene promoters showing significant alterations to DNA methylation were then subjected to Ingenuity Pathway Analysis (Ingenuity System Inc, CA, USA).

Results

The results show that olanzapine causes an increase in methylation in 1,140, 1,294 and 1,313 genes and a decrease in methylation in 633, 565 and 532 genes in the hippocampus, cerebellum and liver, respectively. Most genes affected are tissue specific. Only 41 affected genes (approximately 3%) showed an increase and no gene showed a decrease in methylation in all three tissues. Further, the two brain regions shared 123 affected genes (approximately 10%). The affected genes are enriched in pathways affecting dopamine signalling, molecular transport, nervous system development and functions in the hippocampus; ephrin receptor signalling and synaptic long-term potentiation in the cerebellum; and tissue morphology, cellular assembly and organization in the liver. Also, the affected genes included those previously implicated in psychosis.

Conclusions

The known functions of affected genes suggest that the observed epigenetic changes may underlie the amelioration of symptoms as well as accounting for certain adverse effects including the metabolic syndrome. The results give insights into the mechanism of action of olanzapine, therapeutic effects and the side effects of antipsychotics.

The Ser9Gly polymorphism of the dopamine D3 receptor gene and risk of schizophrenia: an association study and a large meta-analysis

Dopamine D3 receptor (DRD3) binds antipsychotic drugs and is abundant in the limbic system of the brain. It has been shown to play important roles in schizophrenia. A number of studies investigated the Ser9Gly polymorphism of the DRD3 gene to test its possible association with schizophrenia; however, the results were inconsistent. Our study aims to further evaluate the possible association between the Ser9Gly polymorphism and schizophrenia using a case-control association study within the Han Chinese population as well as a meta-analysis covering all previous studies. Our study, based on 329 schizophrenic patients and 288 controls, found no significant difference in the genotype or allele distributions of Ser9Gly polymorphism, the meta-analysis showed that the Ser9Gly polymorphism was not associated with Schizophrenia. Our study does not support the contention that the Ser9Gly polymorphism of the DRD3 gene plays a major role in schizophrenia in the Chinese population.

Dopamine D3 receptor gene Ser9Gly variant and schizophrenia: association study and meta-analysis

OBJECTIVE

To further evaluate the controversial putative association between a Ser9Gly variant in the first exon of the dopamine D3 receptor gene (DRD3) and schizophrenia.

METHODS

Swedish patients with schizophrenia ( n=156) and control subjects ( n=463) were assessed for the DRD3 Ser9Gly variant. Meta-analyses including previous and the present Swedish case-control results were performed.

RESULTS

No significant difference between the Swedish patients and controls were found, but there was an association between DRD3 Ser9Gly Ser/Ser and homozygous genotypes and response to anti-psychotic drugs. This finding was supported by an incomplete meta-analysis. In a meta-analysis of all case-control studies comprising 8761 subjects the association between DRD3 Ser9Gly homozygosity and schizophrenia ( =4.96, degree of freedom=1, p <0.05, odds ratio=1.10, 95% confidence interval=1.01-1.20) persisted. However, the previously proposed association between the Ser/Ser genotype and schizophrenia was not significant (chi2 =2.71, degree of freedom=1, p>0.05, odds ratio=1.08, 95% confidence interval=0.99-1.17).

CONCLUSIONS

Whereas the present Swedish case-control analysis did not yield any evidence for association with the diagnosis, the present meta-analysis suggests that the DRD3 gene confer susceptibility to schizophrenia. Reasons for the discrepancies between prior studies are discussed.

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.

A search for specific and common susceptibility loci for schizophrenia and bipolar disorder: a linkage study in 13 target chromosomes

We report the first stage of a genome scan of schizophrenia (SZ) and bipolar disorder (BP) covering 18 candidate chromosomal areas. In addition to testing susceptibility loci that are specific to each disorder, we tested the hypothesis that some susceptibility loci might be common to both disorders. A total of 480 individuals from 21 multigenerational pedigrees of Eastern Québec were evaluated by means of a consensus best-estimate diagnosis made blind to diagnoses in relatives and were genotyped with 220 microsatellite markers. Two-point and multipoint model-based linkage analyses were performed and mod scores (Z, for max Z(max)) are reported. The strongest linkage signals were detected at D18S1145 (in 18q12; Z = 4.03) for BP, and at D6S334 (in 6p 22-24; Z(het) = 3.47; alpha = 0.66) for SZ. Three other chromosomal areas (3q, 10p, and 21q) yielded linkage signals. Chromosomes 3p, 4p, 5p, 5q, 6q, 8p, 9q, 11q, 11p, 12q, 13q, 18p and 22q showed no evidence of linkage. The 18q12 results met the Lander and Kruglyak (1995) criterion for a genome-wide significant linkage and suggested that this susceptibility region may be shared by SZ and BP. The 6p finding provided confirmatory evidence of linkage for SZ. Our results suggest that both specific and common susceptibility loci must be searched for SZ and BP.

DRD3 and DAT1 genes in schizophrenia: an association study

OBJECTIVE

To investigate the role of the dopamine receptor 3 (DRD3) and transporter 1 (DAT1) genes in schizophrenia or in modulating its phenotype.

METHODS

a Ser9Gly polymorphism in codon 9 of the DRD3 and a VNTR polymorphism in the DAT1genes were examined in two groups of schizophrenic patients, one of excellent neuroleptic responders (N=42) and one of nonresponders (N=64). A group of healthy volunteers screened for major psychiatric disorders was also included (N=89). In addition, age at onset of psychotic symptoms, attention performance and family loading for schizophrenia spectrum disorders were compared between patients with different genotypes in the DRD3 and DAT1 genes.

RESULTS

No significant differences in the allelic distribution of the DRD3 and DAT1 polymorphisms were detected between schizophrenic patients and controls. A trend toward an excess of DRD3 genotype Gly/Gly was observed in neuroleptic nonresponder schizophrenic patients compared to controls (chi(2)=3. 30, df=1, p=0.07). No significant differences in age at onset of psychotic symptoms, attention task performance or family loading for schizophrenia spectrum disorders were observed between groups with different DRD3 and DAT1 genotypes.

CONCLUSION

These results do not support the role of either of these genes in increasing susceptibility to schizophrenia or in modulating its phenotype in the studied population.

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.