The dopamine D4 receptor VNTR in Polish schizophrenia patients

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.

Dopamine D4 and D5 receptor gene variant effects on clozapine response in schizophrenia: replication and exploration

OBJECTIVES

This study aimed to: 1) replicate previously reported associations between dopamine D4 receptor gene (DRD4) polymorphisms and antipsychotic (AP) response in a clozapine (CLZ) response sample; and 2) explore possible associations of polymorphisms across dopamine D5 receptor gene (DRD5) as well as other DRD4 regions.

METHODS

DRD4 exon III 48-bp, intron I (G)(n), and 120-bp repeat polymorphisms, and three DRD4 single nucleotide polymorphisms (SNPs); and DRD5 (CA/CT/GT)(n) microsatellite and four DRD5 SNPs were assessed using standard genotyping and statistical procedures.

RESULTS

We report evidence, which does not survive correction for multiple testing, supporting previous DRD4 findings. Findings of interest include the 120-bp 1-copy allele, intron I (G)(n) 142-bp/140-bp genotype, and exon III 4R allele with CLZ response. All DRD5 tests were negative.

CONCLUSIONS

Overall, these results suggest a possible minor contribution of DRD4 variants, but not DRD5 variants, towards the AP/CLZ response phenotype.

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.

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 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.