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

DRD4 VNTR 4/4 homozygosity as a genetic biomarker for treatment selection in patients with schizophrenia

OBJECTIVE

There seems to be an association between the DRD4 48-bp VNTR polymorphisms and antipsychotic treatment response, but there is a rare reference to confirm this finding. Hence, the present study tried to investigate the association between DRD4 48-bp VNTR polymorphisms and the treatment response of antipsychotics in patients with schizophrenia in Taiwan, using a propensity score matching (PSM) method.

METHODS

A total of 882 participants were enrolled in this study and completed informed consent, research questionnaires, including demographic information and the revised Chinese version Beliefs about Voices Questionnaire, and blood sampling. For descreasing of the selection bias and confounding variables, the PSM nearest neighbor matching method was used to select 765 paitents with schizophrenia (ratio of 1:8 between 85 persistent auditory hallucination and 680 controls) with matched and controlled the age and gender.

RESULTS

Schizophrenia patients with DRD4 4 R homozygosity had a lower rate of good antipsychotic treatment response than the other DRD4 genotype carriers (DRD4 non-4/4). Among those 4 R homozygosity carriers, 60 cases of 503 (11.9%) retain persistent auditory hallucinations. Furthermore, this subgroup of patients is accounted for up to 70.6% of cases with poor neuroleptic treatment response.

CONCLUSIONS

A poor treatment outcome for patients with the 4 R homozygosity had presented,that comparing with those DRD non-4/4 genotype carriers. DRD4 VNTR 4 R homozygosity could be a genetic biomarker to predict poor antipsychotic treatment response in schizophrenia. Patients with DRD 4/4 probably receive novel antipsychotic medications preferentially or in combination with alternative therapy, such as psychotherapy or milieu therapy.

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.

Evaluating the dopamine hypothesis of schizophrenia in a large-scale genome-wide association study

BACKGROUND

The dopamine hypothesis, which posits that dysregulation of the dopaminergic system is etiologic for schizophrenia, is among the most enduring biological theories in psychiatry. Although variation within genes related to dopaminergic functioning has been associated with schizophrenia, an aggregate test of variation, using the largest publicly available schizophrenia dataset, has not previously been conducted.

METHODS

We first identified a core set of 11 genes involved in the synthesis, metabolism, and neurotransmission of dopamine. We then extracted summary statistics of markers falling within, or flanking, these genes from the Psychiatric Genomics Consortium's most recent schizophrenia mega-analysis results. We conducted aggregate tests for enrichment of dopamine-related pathways for association with schizophrenia.

RESULTS

We did not detect significant enrichment of signals across the core set of dopamine-related genes. However, we did observe modest to strong enrichment of genetic signals within the DRD2 locus.

CONCLUSIONS

Within the limits of available power, common sequence variation within core genes of the dopaminergic system is not related to risk of schizophrenia. This does not preclude a role of dopamine, or dopamine-related genes, in the clinical presentation of schizophrenia or in treatment response. However, it does suggest that the genetic risk for schizophrenia is not substantially affected by common variation in those genes which, collectively, critically impact dopaminergic functioning.

Biological mechanisms underlying evolutionary origins of psychotic and mood disorders

Psychotic and mood disorders are brain dysfunctions that are caused by gene environment interactions. Although these disorders are disadvantageous and involve behavioral phenotypes that decrease the reproductive success of afflicted individuals in the modern human society, the prevalence of these disorders have remained constant in the population. Here, we propose several biological mechanisms by which the genes associated with psychotic and mood disorders could be selected for in specific environmental conditions that provide evolutionary bases for explanations of when, why, and where these disorders emerged and have been maintained in humans. We discuss the evolutionary origins of psychotic and mood disorders with specific focuses on the roles of dopamine and serotonin in the conditions of social competitiveness/hierarchy and maternal care and other potential mechanisms, such as social network homophily and symbiosis.

Association of VNTR polymorphisms in DRD4, 5-HTT and DAT1 genes with obesity

OBJECTIVE

To investigate the association between VNTR polymorphisms of DRD4, DAT1 and 5-HTT genes and obesity.

MATERIAL AND METHODS

Peripheral blood samples of 234 obese (BMI ≥ 30) and 148 healthy individuals (BMI ≤ 25) were objected to PCR to detect the VNTR of the 2nd intron of 5-HTT, 3rd exon of DRD4 and 3'UTR of DAT1 genes.

RESULTS

The association between obesity and genotype distributions of 5-HTT, DAT1 and DRD4 genes and between obesity and distributions of allele frequencies were tested by Chi Square (χ(2)) test and were not found statistically significant. BMI values for genotype of obese and morbidly obese (BMI > 40) individuals were analyzed by Kruskal-Wallis and not found statistically significant differences between BMI values for the most frequent genotypes of 5-HTT, DAT1 and DRD4 genes.

CONCLUSIONS

As a conclusion, there was no association between 5-HTT, DAT1 and DRD4 genes VNTR polymorphisms and obesity.

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 D4 receptor gene DRD4 and its association with psychiatric disorders

Dopamine receptors control neural signals that modulates behavior. Dopamine plays an important role in normal attention; that is the reason for studying the genes of the dopaminergic system, mainly in connection with disorders of attention. DRD4 influences the postsynaptic action of dopamine and is implicated in many neurological processes, exhibits polymorphism and is one of the most studied genes in connection with psychiatric disorders. Associations were found with ADHD (attention deficit hyperactivity disorder), substance dependences, several specific personality traits, and reaction to stress. These findings have implications for pharmacogenetics. This article reviews the principle published associations of DRD4 variants with psychiatric disorders.

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.

Association analysis of exon III and exon I polymorphisms of the dopamine D4 receptor locus in Mexican psychotic patients

In this study, we investigated whether polymorphisms of the dopamine D4 receptor (DRD4) gene were associated with psychotic symptomatology rather than with a unique diagnosis such as schizophrenia. A number of association studies between the DRD4 gene 48 bp-VNTR polymorphism at exon 3 and psychotic disorders have been reported, but the results have been controversial. Both 48 bp-VNTR and the 12 bp-VNTR (at exon 1) polymorphisms of this gene were analyzed in a group of 149 unrelated Mexican subjects with a diagnosis of schizophrenia, schizoaffective disorder, schizophreniform disorder, major depression and bipolar disorder, both with psychotic symptoms, brief psychotic disorder, delusional disorder and non-specific psychotic disorder, and in 169 individuals free of psychiatric illnesses. There were no differences in allele or genotype frequencies between groups for the 12 bp-VNTR polymorphisms. However, a significant excess of "rare" alleles (3-, 5-, 6- and 8-48 bp repeats alleles) was found in the group of psychotics. Moreover, haplotypes 3-A1, 5-A1, 6-A1 and 8-A1 were significantly more frequently associated with cases. This positive association supports a role of this molecule as a genetic risk factor in psychotic disorders.

G protein-coupled receptors in major psychiatric disorders

Although the molecular mechanisms underlying psychiatric illnesses such as depression, bipolar disorder and schizophrenia remain incompletely understood, there is increasing clinical, pharmacologic, and genetic evidence that G protein-coupled receptors (GPCRs) play critical roles in these disorders and their treatments. This perspectives paper reviews and synthesizes the available data. Dysfunction of multiple neurotransmitter and neuropeptide GPCRs in frontal cortex and limbic-related regions, such as the hippocampus, hypothalamus and brainstem, likely underlies the complex clinical picture that includes cognitive, perceptual, affective and motoric symptoms. The future development of novel agents targeting GPCR signaling cascades remains an exciting prospect for patients refractory to existing therapeutics.

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.

The dopamine D4 receptor gene 48-base-pair-repeat polymorphism and mood disorders: a meta-analysis

BACKGROUND

We conducted a meta-analysis to re-evaluate the role of the dopamine D4 receptor gene 48-base-pair- repeat (DRD4) polymorphism in mood disorders.

METHODS

DRD4 allele frequencies were compared between 917 patients with unipolar (UP) or bipolar affective disorder (BP) and 1164 control subjects from 12 samples, using the Cochrane Review Manager.

RESULTS

An association was found between all mood disorder groups and DRD4.2. After correcting for multiple testing, the association between DRD4.2 and BP dropped to insignificance; however, the evidence of an association between the DRD4.2 allele and UP (p < .001) and the combined group (p < .001) remained. There was no evidence for heterogeneity or publication bias.

CONCLUSIONS

These findings suggest that the DRD4.2 allele is a risk allele for depression symptomatology. Meta-analysis may be a valuable objective tool for a quantitative summary of evidence for association studies in psychiatric genetics.