No genetic association between dopamine D1 receptor gene and [early onset] schizophrenia

Interaction between BDNF and TNF-α genes in schizophrenia

OBJECTIVE

Our recent work reported that tumor necrosis factor-α (TNF-α) is negatively correlated with brain-derived neurotrophic factor (BDNF) in patients with schizophrenia. A previous study has shown that TNF-α could regulate the extracellular secretion of BDNF. Therefore, we hypothesized that the TNF-α gene (TNF-α) may interact with the BDNF gene (BDNF) to influence schizophrenia risk.

METHODS

We recruited 694 patients with schizophrenia from three mental hospitals in Eastern China and 725 healthy controls. The Positive and Negative Syndrome Scale (PANSS) was employed to evaluate symptom severity. The Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) was performed to assess cognitive function. The SNPs rs6265 in BDNF and rs1799964 in TNF-α were genotyped.

RESULTS

There were no significant differences in allele and genotype frequencies in either rs6265 or rs1799964 between the case and control groups. A significant association of rs6265 AA + AG × rs1799964 CC + CT with schizophrenia was observed (OR = 1.14, 95%CI: 1.02-1.27; P = .02). There were significant differences in the RBANS attention and total scores between the patients with rs6265A and rs1799964C alleles and those without these two alleles (P = .03 and P = .03 after Bonferroni correction, respectively).

CONCLUSION

Our findings provided preliminary evidence that the interaction of BDNF and TNF-α may confer susceptibility to schizophrenia and cognitive dysfunction.

Dopamine-prolactin pathway potentially contributes to the schizophrenia and type 2 diabetes comorbidity

Schizophrenia (SCZ) and type 2 diabetes (T2D) are clinically associated, and common knowledge attributes this association to side effects of antipsychotic treatment. However, even drug-naive patients with SCZ are at increased risk for T2D. Dopamine dysfunction has a central role in SCZ. It is well-known that dopamine constitutively inhibits prolactin (PRL) secretion via the dopamine receptor 2 (DR2D). If dopamine is increased or if dopamine receptors hyperfunction, PRL may be reduced. During the first SCZ episode, low PRL levels are associated with worse symptoms. PRL is essential in human and social bonding, as well as it is implicated in glucose homeostasis. Dopamine dysfunction, beyond contributing to SCZ symptoms, may lead to altered appetite and T2D. To our knowledge, there are no studies of the genetics of the SCZ-T2D comorbidity focusing jointly on the dopamine and PRL pathway in the attempt to capture molecular heterogeneity correlated to possible disease manifestation heterogeneity. In this dopamine-PRL pathway-focused-hypothesis-driven review on the association of SCZ with T2D, we report a specific revision of what it is known about PRL and dopamine in relation to what we theorize is one of the missing links between the two disorders. We suggest that new studies are necessary to establish the genetic role of PRL and dopamine pathway in SCZ-T2D comorbidity.

Research in China on the molecular genetics of schizophrenia

Schizophrenia is a complex disease caused by genetic and environmental factors with a global heritability of more than 80%. By the end of the 1970s, Chinese scientists reported a heritability of schizophrenia of 82.9% in the Chinese Han population. Continuous improvements in research techniques and the recruitment of larger samples have made it possible for Chinese scientists to identify a number of candidate susceptibility genes for schizophrenia. This article reviews the results in genetic research of schizophrenia by Chinese scientists over the last five decades

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.

Metabolic syndrome in patients taking clozapine: prevalence and influence of catechol-O-methyltransferase genotype

RATIONALE

Metabolic syndrome (MetS) has consistently been identified as an adverse effect of long-term treatment with atypical antipsychotics (AAPs) such as clozapine. Elevated serum homocysteine concentration has been found to act as an independent risk factor for MetS, and catechol-O-methyltransferase (COMT) catalyzes the homocysteine metabolism. We accordingly hypothesized that COMT dysregulation may confer the susceptibility to MetS induced by AAPs, potentially in a gender-specific manner, because the interaction effects of COMT and gender have been consistently reported.

OBJECTIVES

This study aimed at determining the prevalence and influence of COMT on MetS among a population undergoing long-term clozapine treatment.

METHODS

A total of 468 schizophrenia patients taking clozapine were divided into two groups, those experiencing MetS and non-MetS. We genotyped three functional variants (rs4633, rs4680, and rs4818) in COMT and measured the serum levels of fasting homocysteine, glucose, triglyceride (TG), and high-density lipoprotein cholesterol.

RESULTS

MetS was found in 202/468 (43.2 %) of all the patients, with 40.2 % prevalence (138/343) in males and 51.2 % (64/125) in females. Patients with MetS had notably higher metabolic parameters than those without MetS. The mean levels of homocysteine in patients with MetS were significantly higher than those without MetS. We found a positive association between the rs4680 polymorphism and the serum triglyceride levels (corrected P = 0.024). Further analysis revealed that the rs4680 Met allele was significantly associated with increased triglyceride levels among female patients (P = 0.009), but not among males (P = 0.07).

CONCLUSIONS

Our findings suggest a potential association between rs4680 in COMT and elevated TG levels, particularly among female patients.

Association of dopamine D1 receptor gene polymorphism with schizophrenia: a meta-analysis

To date, the role of dopamine D1 receptor (DRD1) polymorphism in schizophrenia remains controversial. We carried out a meta-analysis to determine whether DRD1 polymorphism influences the risk of schizophrenia. We examined whether rs4532 and rs5326 genetic variants are related to the etiology of schizophrenia, using a meta-analysis. Relevant case-control studies were retrieved by database searching and selected according to established inclusion criteria. A total of ten studies were identified and included in our meta-analysis, nine for rs4532, with 1,941 cases and 2,480 controls, and four for rs5326, with 1,285 cases and 1,195 controls. No significant association was found between the rs4532 locus and schizophrenia. For the rs5326 locus, the guanine-adenine (GA) genotype was associated with schizophrenia as a risk factor (for GA vs guanine-guanine [GG], odds ratio [OR] =1.36, 95% confidence interval [CI]: 1.15-1.61, P<0.001). The GA genotype of rs5326 increased the risk of schizophrenia, but there was no association between rs4532 and schizophrenia. These data may provide references for case-control studies in schizophrenia in future.

Association study of OPRM1 polymorphisms with Schizophrenia in Han Chinese population

BACKGROUND

The expression of μ-opioid receptor has important role in cognitive dysfunction in Schizophrenia (SZ). The results of studies about the association of polymorphisms of μ-opioid receptor gene (OPRM1) with SZ were inconsistent.

METHODS

We conducted a case-control study to investigate the genetic association between OPRM1 polymorphisms and SZ among the Han chinese population. 264 SZ patients and 264 age-matched control subjects were recruited. Four SNPs of OPRM1 were successfully genotyped by using PCR-RFLP.

RESULTS

Of four polymorphisms, rs1799971 and rs2075572 were shown to associate with SZ. Compared with the A allele of rs1799971 and C allele of rs2075572, the G allele of rs1799971 and rs2075572 was associated with an almost 0.46-fold risk (OR=0.46, 95% CI: 0.357-0.59, P<0.01) and 0.7-fold risk (OR=0.707, 95% CI: 0.534-0.937, P=0.015) of the occurrence of SZ,. When subjects were divided by gender, rs1799971 remained significant difference only in males (OR=0.309, 95% CI: 0.218-0.439 for G allele, P<0.01), and rs2075572 only in females (OR=0.399, 95% CI: 0.246-0.648 for G allele, P<0.01). In secondary analysis with subsets of patients, the G allele of rs1799971 (compared to the A allele) was associated with a decreased risk of all patients and male patients with apathy symptoms (OR=0.086, 95% CI: 0.048-0.151, P=0.01; OR=0.083, 95% CI: 0.045-0.153, P<0.01), and the G allele of rs2075572 (compared to the C allele) was associated with a decreased risk of all patients and female patients with positive family history (OR=0.468, 95% CI: 0.309-0.71, P<0.01; OR=0.34, 95% CI: 0.195-0.593, P<0.01). In addition, haplotype analysis revealed that two SNP haplotypes (A-C-C-G and G-C-C-A) were associated with decreased risks of SZ (P<0.01). The other two (G-C-C-G and G-G-C-G) with increased risks of SZ (P<0.01).

CONCLUSIONS

The present study demonstrated for the first time that the OPRM1 polymorphism may be a risk factor for schizophrenia in the Han Chinese. Further studies are needed to give a global view of this polymorphism in pathogenesis of schizophrenia in a large-scale sample, family-based association design or well-defined subgroups of schizophrenia.

T102C polymorphism of serotonin 2A type receptor gene confers susceptibility to (early onset) schizophrenia in Han Chinese: an association study and meta-analysis

INTRODUCTION

Several lines of evidence have indicated that serotonin 2A receptor (HTR2A) may be involved in the pathophysiology of schizophrenia. One functional polymorphism in HTR2A (T102C) has been widely investigated; however, the results have been inconsistent. The purpose of this study was to evaluate the association between HTR2A T02C polymorphism and schizophrenia in a Chinese Han population.

METHODS

We performed a case-control study, using an early onset sample, which may be an attractive subgroup for genetic studies. In addition, we performed a meta-analysis of the combined sample groups in Han Chinese.

RESULTS

Our study, based on 385 schizophrenic patients and 399 controls, found a significant genotype-wise association of T102C and schizophrenia (P = 0.02). After applying stratified analyses, the dominant model for T allele produced significant association (OR = 1.60, 95%CI = 1.11-2.30, P = 0.01). In the meta-analysis including all of the published population-based association studies in Han Chinese and the present association study, the pooled genotype-wise result in a dominant model was statistically significant with a summary OR of 1.25 (95%CI = 1.04-1.50, P = 0.02).

DISCUSSION

Our results suggest that the HTR2A T102C polymorphism may confer susceptibility to schizophrenia in Han Chinese.

Preliminary evidence for association between schizophrenia and polymorphisms in the regulatory Regions of the ADRA2A, DRD3 and SNAP-25 Genes

The results of linkage and candidate gene association studies have led to a range of hypotheses about the pathogenesis of schizophrenia. We limited our study to polymorphisms in candidate genes involved in dopaminergic and noradrenergic systems, and in the 25KDa synaptosomal-associated protein (SNAP-25) gene that is related to neurotransmitter exocytosis. Eight single nucleotide polymorphisms (SNPs) in regulating or coding regions of genes for the alpha-2A adrenergic receptor (ADRA2A), dopamine receptors D1 and D3 (DRD1 and DRD3), dopamine β-hydroxylase (DBH) and SNAP-25 were genotyped in male patients with schizophrenia (n=192) and in healthy controls (n=213). These polymorphisms were previously associated with schizophrenia. The allelic association between schizophrenia and ADRA2A rs1800544 polymorphism, SNAP-25 rs1503112 polymorphism, and DRD3 rs6280 polymorphism was found in our study. However, only observations for rs1503112 survived correction for multiple testing. Association was also evaluated by considering the polymorphisms as interactions; in this case, a likelihood ratio test (LRT) revealed evidence for association with schizophrenia in four polymorphism combinations: two DRD3*SNAP-25 combinations (rs6280*rs3746544 and rs6280*rs3746544, P=0.02), one ADRA2A*SNAP25 combination (rs1800544*rs3746544) and one ADRA2A*DBH combination (rs1800544*rs2519152). Our results are in agreement with the previously proposed role of DNA polymorphisms involved in dopaminergic, noradrenergic and synaptic functions in the pathogenesis of schizophrenia. Further relevant studies including larger sample size and more markers are needed to confirm our results.

Association between BDNF Val66Met polymorphism and cognitive performance in antipsychotic-naïve patients with schizophrenia

Cognitive impairment is one of the core symptoms in schizophrenia, which reflects the neurodevelopmental deficits in the etiology of this disease. Brain-derived neurotrophic factor (BDNF) plays an important role in various neurodevelopmental processes. Growing evidence has shown that BDNF may be involved in the etiology of schizophrenia. The aim of this study was to examine the association of the BDNF Val66Met polymorphism with cognition in patients with schizophrenia. Various neuropsychological tests including the Wechsler Adult Intelligence Scale-Revised, the Wechsler Memory Scale-Revised, and the Wisconsin Card Sorting Test (WCST) were employed in a sample of 112 antipsychotic-naïve patients with schizophrenia and 63 healthy controls. We examined the Val66Met polymorphism in the 112 patients and 394 controls. Among the patients, cognition was compared between Met allele carriers and non-Met allele carriers. A wide range of cognitive deficits were demonstrated in the schizophrenic patients, compared with the controls (Ps < 0.01). No significant differences of genotype or allele distribution were identified between patients and controls. The patients with Met allele showed more percent WCST perseverative errors than those without Met allele (P = 0.007). After stratification based on gender, an association between the Met allele and a higher percentage of perseverative errors was found in male patients (P = 0.014), but not in females (P = 0.09). Cognitive performance is broadly impaired in schizophrenic patients. The BDNF Val66Met polymorphism may be involved in the impaired executive function. This effect may have gender-specific characteristics.

An association study between dopamine D1 receptor gene polymorphisms and the risk of schizophrenia

Deficits in dopamine transmission at D1 receptors in the PFC are implicated in schizophrenia. Genetic polymorphisms in functional regions of DRD1 have a plausible role in modulating the risk of schizophrenia. In order to evaluate the role of DRD1 polymorphisms as a risk factor for schizophrenia, we performed a detailed analysis of possible functional single nucleotide polymorphisms (SNPs) in regulatory and coding regions of DRD1. Nine SNPs were identified by DNA sequencing in 20 patients with schizophrenia. Then 385 cases and 350 healthy control subjects were genotyped using the nine SNPs (rs4867798, rs686, rs1799914, rs4532 rs5326, rs265981, rs10078714, rs10063995, rs10078866). Statistically significant differences were observed in the allelic or genotypic frequencies of the rs686 and rs10063995 polymorphism in the DRD1 gene. A significantly lower risk of schizophrenia was associated with the G allele and AG+GG genotype of rs686 (OR (G allele)=0.632, 95%CI (G allele): 0.470-0.849; OR (AG+GG genotype)=0.578, 95%CI (AG+GG genotype): 0.416-0.803) compared with the A allele and AA genotype, respectively. And a significantly increased risk of schizophrenia was associated with the T allele of rs10063995 (OR=1.446, 95%CI: 1.125-1.859) compared with the G allele. The haplotype analysis indicated the G-T variant containing the T allele of rs10063995 is a risk for schizophrenia (P=0.005, OR=1.467, 95%CI: 1.123-1.917). These data suggest that DRD1 gene polymorphisms confer susceptibility to schizophrenia, and also support the notion that dysfunction of DRD1 is involved in the pathophysiological process of schizophrenia.

Lack of effect of brain derived neurotrophic factor (BDNF) Val66Met polymorphism on early onset schizophrenia in Chinese Han population

Schizophrenia is a chronic psychiatric disorder with high heritability. Schizophrenic patients with early-age onset tend to have a greater genetic component and may be an attractive subpopulation for genetic studies. Brain-derived neurotrophic factor (BDNF) is considered a candidate gene for schizophrenia. A single nucleotide polymorphism (BDNF Val66Met) was reported to be associated with schizophrenia, although discrepancy remains. The aim of this study was to evaluate the association between BDNF Val66Met polymorphism and schizophrenia using an early onset sample in the Chinese Han population. Our sample consisted of 353 schizophrenic patients with onset before age 18 and 394 healthy controls. All subjects were of an ethnically homogenous Han Chinese origin. No significant differences of genotype or allele distribution were identified between the patients and controls. However, the Met allele was significantly associated with an earlier age of onset in male schizophrenic patients (Kaplan-Meier log-rank test P=0.005), but not in females (P=0.289). The BDNF Val66Met polymorphism has an important effect on the age of onset of schizophrenia in a gender-specific manner. This may represent a significant genetic clue for the etiology of schizophrenia and thus, further studies are required to uncover the exact role of BDNF in the development of schizophrenia.

Associations between DRDs and schizophrenia in a Korean population: multi-stage association analyses

The dysregulation of the dopaminergic system has been implicated in the pathophysiology of major psychosis, including schizophrenia, with dopamine receptor genes (DRDs) presently targeted as the most promising candidate genes. We investigated DRD1-5 for association with schizophrenia using a multi-stage approach in a Korean sample. One hundred forty-two SNPs in DRD1-5 were selected from the dbSNP, and the associations of each SNP were then screened and typed by MALDI-TOF mass spectrometry using pooled DNA samples from 150 patients with major psychosis and 150 controls. Each of the suggested SNPs was then genotyped and tested for an association within the individual samples comprising each pool. Finally, the positively associated SNPs were genotyped in an extended sample of 270 patients with schizophrenia and 350 controls. Among the 142 SNPs, 88 (62%) SNPs in our Korean population were polymorphic. At the pooling stage, 10 SNPs (DRD1: 2, DRD2: 3, and DRD4: 5) were identified (P<0.05). SNPs rs1799914 of DRD1 (P=0.046) and rs752306 of DRD4 (P=0.017) had significantly different allele frequencies in the individually genotyped samples comprising the pool. In the final stage, with the extended sample, the suggestive association of DRD4 with rs752306 was lost, but the association of DRD1 with rs1799914 gained greater significance (P=0.017). In these large-scale multi-stage analyses, we were able to find a possible association between DRD1 and schizophrenia. These findings suggested the potential contribution of a multi-step strategy for finding genes related to schizophrenia.