Association analysis of a functional G protein beta3 subunit gene polymorphism (C825T) in mood disorders

Using literature-based discovery to identify candidate genes for the interaction between myocardial infarction and depression

Background

A multidirectional relationship has been demonstrated between myocardial infarction (MI) and depression. However, the causal genetic factors and molecular mechanisms underlying this interaction remain unclear. The main purpose of this study was to identify potential candidate genes for the interaction between the two diseases.

Methods

Using a bioinformatics approach and existing gene expression data in the biomedical discovery support system (BITOLA), we defined the starting concept X as “Myocardial Infarction” and end concept Z as “Major Depressive Disorder” or “Depressive disorder”. All intermediate concepts relevant to the “Gene or Gene Product” for MI and depression were searched. Gene expression data and tissue-specific expression of potential candidate genes were evaluated using the Human eFP (electronic Fluorescent Pictograph) Browser, and intermediate concepts were filtered by manual inspection.

Results

Our analysis identified 128 genes common to both the “MI” and “depression” text mining concepts. Twenty-three of the 128 genes were selected as intermediates for this study, 9 of which passed the manual filtering step. Among the 9 genes, LCAT, CD4, SERPINA1, IL6, and PPBP failed to pass the follow-up filter in the Human eFP Browser, due to their low levels in the heart tissue. Finally, four genes (GNB3, CNR1, MTHFR, and NCAM1) remained.

Conclusions

GNB3, CNR1, MTHFR, and NCAM1 are putative new candidate genes that may influence the interactions between MI and depression, and may represent potential targets for therapeutic intervention.

Polymorphisms of 5-HTT LPR and GNβ3 825C>T and Response to Antidepressant Treatment in Functional Dyspepsia: A Study from The Functional Dyspepsia Treatment Trial

OBJECTIVES

The Functional Dyspepsia Treatment Trial reported that amitriptyline (AMI) was associated with adequate relief of functional dyspepsia (FD) symptoms, but the pharmacogenetics of antidepressant response in FD are not known. GNβ3 825C>T CC genotype has been previously linked to FD and TT genotype to antidepressant response in depression. The ss genotype of the 5-HTT LPR variant of the serotonin transporter gene (SLC6A4) has been linked to selective serotonin reuptake inhibitor (SSRI) response. We aimed to examine whether GNβ3 825C>T and 5-HTT LPR polymorphisms result in differential treatment effects in FD patients receiving antidepressant therapy.

METHODS

Participants were randomized to receive placebo, 50 mg AMI, or 10 mg escitalopram (ESC). The primary end point was adequate relief for ≥5 weeks of the last 10 weeks. Genotyping of GNβ3 825C>T and 5-HTT LPR was performed utilizing PCR-based methods.

RESULTS

GNβ3 825C>T and 5-HTT LPR genotype data were available for 256 (88%) and 246 (84%) patients, respectively. Both polymorphisms were in Hardy-Weinberg equilibrium. In tests for differential treatment, neither 5-HTT LPR nor GNβ3 825C>T genotype influenced response to therapy (P=0.89 and P=0.54, respectively). Although there was a tendency for a more favorable response to ESC in the SS/LS genotype compared to the LL genotype groups (40% vs. 31% reporting adequate relief of FD symptoms) among those in the ESC treatment arm, this was not significant (P=0.43).

CONCLUSIONS

GNβ3 825C>T and 5-HTT LPR genetic variants do not alter treatment response to tricyclic and SSRI antidepressants in FD.

Functional dyspepsia is associated with GNβ3 C825T and CCK-AR T/C polymorphism

BACKGROUND

A polymorphism (C825T) in G-protein β polypeptide-3 (GNβ3) gene alters intracellular signal transduction, which may cause motor or sensory abnormalities in the gastrointestinal tract. Cholecystokinin-A receptor (CCK-AR) gene T/C polymorphism is associated with a defective splicing of the primary transcript of CCK-AR mRNA, which may modulate satiety signal and delay gastric emptying. Therefore, we evaluated the role of these polymorphisms in patients with functional dyspepsia (FD) as compared with healthy controls (HC).

PATIENTS AND METHODS

A total of 237 consecutive patients with FD (Rome III) and 250 HC were genotyped for GNβ3 C825T and CCK-AR T/C polymorphisms (PCR-RFLP).

RESULTS

Patients with FD [173 (73%) men, age: 38 ± 12 years] were comparable with HC [195 (78%) men, age: 37 ± 12 years] with respect to age and sex. Out of 237 patients, 26 (11%) had epigastric pain syndrome (EPS), 55 (23.2%) had postprandial distress syndrome (PDS), and 156 (65.8%) had EPS-PDS overlap. Among 237 patients with FD, TT genotype (associated with increased intracellular signal transduction) of GNβ3 C825T polymorphism was more common among patients than among HC [26 (11%) vs. 12 (4.8%), P=0.014; odds ratio (OR): 2.47, 95% confidence interval (CI): 1.2-5.1]. CC (variant) genotype of CCK-AR T/C polymorphism was infrequent among patients than among HC [19 (8%) vs. 46 (18.4%), P=0.001; OR: 0.36, 95% CI: 0.19-0.66]. However, these polymorphisms were comparable among patients with different subtypes of FD (P=0.80 and 0.44).

CONCLUSION

TT genotype of GNβ3 C825T is more common among patients with FD than among HC, suggesting that increased signal transduction associated with this genotype may be important in its pathophysiology. However, CCK-AR polymorphism is protective against FD.

The C825T Polymorphism of the G-Protein β3 Gene as a Risk Factor for Depression: A Meta-Analysis

Background

TheG-protein β3 gene (GNβ3) has been implicated in psychiatric illness through its effects upon intracellular transduction of several neurotransmitter receptors. Multiple studies have investigated the relationship of the C825T polymorphism of the GNβ3 gene (GNβ3 C825T) to depression and antidepressant response. However, the relationship between GNβ3 C825T and depression remains inconsistent. Therefore, here we performed a meta-analysis to investigate the role of GNβ3 C825Tin depression risk.

Methods

Published case-control studies examining the association between GNβ3 C825T and depression were systematically searched for through several electronic databases (PubMed, Scopus, Science Direct, Springer, Embase, psyINFO, and CNKI). The association between GNβ3 C825T and depression risk were assessed by odd ratios (ORs) and their 95% confidence intervals (CIs) for each study. Pooled ORs were constructed for allele contrast (C versus T), homozygote (CC versus TT) model, heterozygote (CC versus CT) model, dominant model (CC + CT versus TT), and recessive (CC versus TT+CT) model. In order to evaluate possible biases, a sensitivity analysis was conducted by sequential deletion of individual studies in an attempt to assess the contribution of each individual dataset to the pooled OR.

Results

Nine studies, including 1055 depressed patients and 1325 healthy controls, were included. A significant association between GNβ3 C825Tand depression was found to exist, suggesting that the T-allele of GNβ3 C825Tcan increase susceptibility to depression. After stratification by ethnicity, the same association was found in the Asian subpopulation, but not the Caucasian subpopulation.

Conclusions

This is the first meta-analysis to reveal a relationship between GNβ3 C825T and depression. Asian T-allele carriers of GNβ3 C825T appear to be more susceptible to depression.

Purinergic system dysfunction in mood disorders: a key target for developing improved therapeutics

Uric acid and purines (such as adenosine) regulate mood, sleep, activity, appetite, cognition, memory, convulsive threshold, social interaction, drive, and impulsivity. A link between purinergic dysfunction and mood disorders was first proposed a century ago. Interestingly, a recent nationwide population-based study showed elevated risk of gout in subjects with bipolar disorder (BD), and a recent meta-analysis and systematic review of placebo-controlled trials of adjuvant purinergic modulators confirmed their benefits in bipolar mania. Uric acid may modulate energy and activity levels, with higher levels associated with higher energy and BD spectrum. Several recent genetic studies suggest that the purinergic system - particularly the modulation of P1 and P2 receptor subtypes - plays a role in mood disorders, lending credence to this model. Nucleotide concentrations can be measured using brain spectroscopy, and ligands for in vivo positron emission tomography (PET) imaging of adenosine (P1) receptors have been developed, thus allowing potential target engagement studies. This review discusses the key role of the purinergic system in the pathophysiology of mood disorders. Focusing on this promising therapeutic target may lead to the development of therapies with antidepressant, mood stabilization, and cognitive effects.

Pharmacogenomics of bipolar disorder

Bipolar disorder (BD) is a lifelong severe psychiatric condition with high morbidity, disability and excess mortality. The longitudinal clinical trajectory of BD is significantly modified by pharmacological treatment(s), both in acute and in long-term stages. However, a large proportion of BD patients have inadequate response to pharmacological treatments. Pharmacogenomic research may lead to the identification of molecular predictors of treatment response. When integrated with clinical information, pharmacogenomic findings may be used in the future to determine the probability of response/nonresponse to treatment on an individual basis. Here we present a selective review of pharmacogenomic findings in BD. In light of the evidence suggesting a genetic effect of lithium reponse in BD, we focused particularly on the pharmacogenomic literature relevant to this trait. The article contributes a detailed overview of the current status of pharmacogenomics in BD and offers a perspective on the challenges that can hinder its transition to personalized healthcare.

Pharmacogenetics of antidepressant drugs: current clinical practice and future directions

While antidepressants are widely used to treat mood and anxiety disorders, only half of the patients will respond to antidepressant treatment and only one-third of patients experience a full remission of symptoms. The identification of genetic biomarkers that predict antidepressant-treatment response can improve current clinical practice. This is an emerging field known as pharmacogenetics, which comprises of genetic studies on both the pharmacokinetics and pharmacodynamics of treatment response. Recent studies on antidepressant-treatment response have focused on both aspects of pharmacogenetics research, identifying new candidate genes that may predict better treatment response for patients. This paper reviews recent findings on the pharmacogenetics of antidepressant drugs and future clinical applications. Ultimately, these studies should lead to the use of genetic testing to guide the use of antidepressants in clinical practice.

SNPs in genes encoding G proteins in pharmacogenetics

Heterotrimeric guanine-binding proteins (G proteins) transmit signals from the cell surface to intracellular signal cascades and are involved in various physiological and pathophysiological processes. Polymorphisms in the genes GNB3 (encoding the Gβ3 subunit), GNAS (encoding the Gαs subunit) and GNAQ (encoding the Gαq subunit) have been the primary focus of investigation. Polymorphisms in these genes could be associated with different complex phenotypes underlining that alterations in G-protein signaling can cause multiple disorders. G proteins present a point of convergence or ‘bottleneck’ between various receptors and effectors, thus making them a sensible tool for pharmacogenetic studies. The pharmacogenetic studies performed to date mostly demonstrate an association between G-protein polymorphisms and response to therapy or occurrence of adverse drug effects. Therefore, polymorphisms in genes encoding G-protein subunits may help to individualize drug treatment in various diseases with regard to both efficacy and safety.

The G-protein beta3 subunit 825 TT genotype is associated with epigastric pain syndrome-like dyspepsia

Background

Although familial clustering of functional dyspepsia (FD) has been reported, the role of genetics in the susceptibility to FD is still not well understood. Several reports indicate an association between FD and G-protein β3 (GNB3) subunit gene polymorphism (C825T); however, these studies had small sample sizes and the findings are inconclusive. In the present study we clarified the association between GNB3 gene polymorphism and dyspepsia in a large population of Japanese subjects who visited a hospital for annual health check-up.

Methods

Subjects with significant upper gastrointestinal findings were excluded. Subjects with dyspeptic symptoms were divided into either a postprandial distress syndrome (PDS) group or an epigastric pain syndrome (EPS) group according to the Rome III criteria. The presence of the GNB3 C825T polymorphism was then evaluated and logistic regression analysis was used to test all variables.

Results

The GNB3 genotype distribution in subjects without dyspepsia was 191 CC (25.1%), 368 TC (48.4%), and 202 TT (26.5%) and 17 CC (25.0%), 29 TC (42.6%), and 22 TT (32.4%) in subjects with dyspepsia. No significant correlation was found between the GNB3 825TT genotype and dyspepsia. However, the TT genotype was significantly associated with subjects with EPS-like symptoms (odds ratio (OR) = 2.00, 95% confidence interval (CI); 1.07-3.76) compared to the CT/CC genotype adjusted for gender and age. No significant correlation was found between GNB3 polymorphism and PDS-like symptoms (OR = 0.68, 95% CI; 0.31-1.51). With the exclusion of subjects with both EPS- and PDS-like symptoms, only the TT genotype was significantly associated with EPS-like symptoms (OR = 2.73, 95% CI; 1.23-5.91).

Conclusion

The homozygous GNB3 825T allele influences the susceptibility to EPS-like dyspepsia.

G-protein gene 825C>T polymorphism is associated with response to clozapine in Brazilian schizophrenics

AIMS

Clozapine treatment of schizophrenia is effective only in 30-60% of individuals. Since genetic factors are believed to play a significant role in the variation of response to antipsychotics, the aim of the present study was to verify the effect of a G-protein gene polymorphism on clozapine response and clozapine-induced generalized seizures in Brazilian patients with schizophrenia.

PATIENTS & METHODS

In total, 121 schizophrenic patients in treatment with clozapine were genotyped for the 825C>T polymorphism it the GNB3 gene using PCR.

RESULTS

Homozygosity for the T825 allele was more frequent among nonresponders (chi(2) = 7.708; p = 0.021), and carriers of this allele had a higher risk to present a convulsion episode (chi(2) = 7.279; p = 0.007). These results were confirmed after controlling for covariates by logistic regression.

CONCLUSION

Our data suggest an influence of the 825C>T polymorphism on clozapine response in persons with schizophrenia and also on a specific neurological side effect (generalized seizures) under clozapine treatment.

Meta-analyses of genetic studies on major depressive disorder

The genetic basis of major depressive disorder (MDD) has been investigated extensively, but the identification of MDD genes has been hampered by conflicting results from underpowered studies. We review all MDD case-control genetic association studies published before June 2007 and perform meta-analyses for polymorphisms that had been investigated in at least three studies. The study selection and data extraction were performed in duplicate by two independent investigators. The 183 papers that met our criteria studied 393 polymorphisms in 102 genes. Twenty-two polymorphisms (6%) were investigated in at least three studies. Seven polymorphisms had been evaluated in previous meta-analyses, 5 of these had new data available. Hence, we performed meta-analyses for 20 polymorphisms in 18 genes. Pooled odds ratios (ORs) with 95% confidence intervals (CIs) were calculated. Statistically significant associations were found for the APOE varepsilon2 (OR, 0.51), GNB3 825T (OR, 1.38), MTHFR 677T (OR, 1.20), SLC6A4 44 bp Ins/Del S (OR, 1.11) alleles and the SLC6A3 40 bpVNTR 9/10 genotype (OR, 2.06). To date, there is statistically significant evidence for six MDD susceptibility genes (APOE, DRD4, GNB3, MTHFR, SLC6A3 and SLC6A4).

Study on the interrelationship between 5-HTTLPR/G-protein beta3 subunit (C825T) polymorphisms and depressive disorder

OBJECTIVE

To assess whether the promoter region of the serotonin transporter gene (5-HTTLPR) and G-protein beta3-subunit (GNbeta3 C825T) polymorphisms are associated with depressive disorder and explore the genetic mechanism concerning the pathogenesis of this disorder.

METHODS

The genotypes were determined with polymerase chain reaction and allele-specific restriction enzyme analysis. Patients suffering from depression (n=184) and sex and age-matched controls (n=158) were compared in this study.

RESULTS

The frequencies of 5-HTTLPR SS and GNbeta3 825TT genotypes and 5-HTTLPR S and GNbeta3 825T alleles in patients suffering from depression were significantly higher than those in the controls (P<0.01). Combined genotype analysis showed that individuals with both 5-HTTLPR S and GNbeta3 825T alleles (odds ratio=3.25, P=0.002) had a risk of depressive disorder higher than those with 5-HTTLPR S (odds ratio=1.817, P=0.01) or GNbeta3 825T alleles (odds ratio=2.214, P=0.001) alone.

CONCLUSIONS

These results indicated that the etiology of depressive disorder is associated with 5-HTTLPR and GNbeta3 C825T polymorphisms. Our data also suggests that an interaction effect may exist between the 5-HTTLPR S allele and GNbeta3 825T allele in increasing the risk of depressive disorder.

Interaction between TPH1 and GNB3 genotypes and electroconvulsive therapy in major depression

We studied the association between tryptophan hydroxylase 1 (TPH1) A218C and G-protein beta-3 subunit (GNB3) C825T polymorphisms and treatment response in electroconvulsive therapy (ECT). The sample consisted of 119 patients with major depressive disorder (MDD) and 398 controls. Neither TPH1 nor GNB3 polymorphisms are associated with treatment response. However, subjects carrying TPH1 CC genotype are more likely to belong to the patient sample than to the controls. In female subjects, T-allele of GNB3 polymorphism increases the risk of being a treatment-resistant patient with MDD. Moreover, in females the combination of TPH1 CC and GNB3 CT + TT genotype is associated with an increased risk of belonging to the patient group.

The GNB3 C825T polymorphism and depression among subjects with alcohol dependence

The T allele of the C825T polymorphism in the G-protein beta(3) subunit gene (GNB3) is related to the increase of signal transduction by the G-protein. G-proteins are intermediary paths in signal transduction from receptors involved in mood regulation and substance dependence. We studied the C825T polymorphism in individuals with (i) alcohol and nicotine dependence (n = 109), (ii) nicotine dependence only (n = 117) and (iii) non-dependent controls (n = 108). We also tested for possible associations with psychiatric comorbidities among alcohol-dependent individuals. No differences were detected for allele and genotype frequencies in individuals with or without dependencies. Alcohol-dependent individuals with the heterozygous genotype presented more frequently major depressive disorder (chi(2) = 12.34; p = 0.002). These findings, taken together with other studies suggesting an influence of the C825T polymorphism in major depressive disorder, support the hypothesis of the involvement of G-proteins in mood regulation.

Association between a functional polymorphism in the renin-angiotensin system and completed suicide

Suicide has been suggested to involve disturbances in the stress response system and to be related to genetics. The renin-angiotensin system (RAS) has been shown to affect the stress response, and several functional polymorphisms in RAS-related genes have been predicted to alter protein function. We hypothesized that the dysregulation of RAS was involved in suicide, and examined the association between completed suicides and four functional polymorphisms of RAS-related genes: the angiotensinogen M235T, angiotensin-converting enzyme (ACE) insertion(I)/deletion(D), angiotensin type-1 receptor A1166C, and G-protein-beta3 C825T gene polymorphisms. The I allele of the ACE I/D polymorphism was found to be more frequent in completed suicides than in controls (P = 0.014). The I allele was also found to be more frequent in male completed suicides (P = 0.022) than in male controls, while this was not the case in females. These results suggest that the alteration of RAS function caused by the genetic polymorphism is involved in the susceptibility to suicide in males.

Studies of the association of the GNB3 825C>T polymorphism with components of the metabolic syndrome in white Danes

AIMS/HYPOTHESIS

The 825C>T polymorphism in the gene encoding the G protein beta3 subunit (GNB3) causes enhanced G protein activation and increased in vitro cell proliferation. This polymorphism is also repeatedly associated with an increased risk of hypertension and has been studied in relation to obesity with divergent results. Only a few association studies have investigated whether this polymorphism is related to type 2 diabetes or the metabolic syndrome. We estimated the impact of the GNB3 825C>T polymorphism in relatively large-scale association studies of common phenotypes of the metabolic syndrome.

MATERIALS AND METHODS

The GNB3 825C>T polymorphism was genotyped in 7,518 white Danish subjects using mass spectrometry analysis of PCR products. Case-control studies were undertaken for obesity, hypertension, type 2 diabetes and the metabolic syndrome, and a meta-analysis including data from the present study and previous studies of hypertension was performed. Quantitative trait studies of metabolic variables were carried out in 4,387 glucose-tolerant subjects.

RESULTS

We observed minor differences in 825C>T genotype distributions for type 2 diabetes (CC/CT/TT 49/41/10% (control) vs 46/46/9% (cases), respectively, p=0.007); however, after correction for multiple testing, these were not statistically significant. No association was found with hypertension, obesity or the metabolic syndrome. Curiously, the T allele was associated with nominally lower systolic and diastolic blood pressure levels-a finding in contrast with most previous studies-but not with other metabolic variables. Meta-analysis demonstrated a high degree of heterogeneity between study populations of different ethnic origin. Although there was a tendency towards an increased risk of hypertension among 825T allele carriers, this was not statistically significant.

CONCLUSIONS/INTERPRETATION

The present study suggests no major involvement of the GNB3 825C>T polymorphism in components of the metabolic syndrome.

The involvement of G proteins and regulators of receptor-G protein coupling in the pathophysiology, diagnosis and treatment of mood disorders

Biochemical research in mood disorders has focused, along the cascade of events involved in signal transduction, from studies at the level of the monoamine neurotransmitter to the level of the neurotransmitter receptors, and lately to information transduction mechanisms beyond receptors, involving the coupling of receptors with signal transducers. We review findings concerning (a) the involvement of G proteins, in the pathophysiology, diagnosis and treatment of mood disorders; (b) the importance of regulation of receptor-G protein coupling, G protein-coupled receptor kinases (GRKs), beta-arrestins, to the pathophysiology of mood disorders and the mechanism of action of antidepressants. We relate to the special complexity of mental disorders with regards to etiology and pathophysiological diagnosis as well as to the strength and limitations of the 'pharmacological bridge' approach governing studies to unravel the etiology of mental disorders. There are presently no established and reliable, sensitive and specific objective biological diagnostic markers in psychiatry that can serve as 'gold standards'. The future achievement of an objective biochemical differential diagnostic system for major mental disorders that will also enable an objective biological treatment monitoring is expected to be revolutionary for psychiatry with a magnitude similar to the impact of the discovery of psychopharmacological treatments for mental disorders more than 50 years ago.

Response to fluoxetine and serotonin 1A receptor (C-1019G) polymorphism in Taiwan Chinese major depressive disorder

Serotonin systems appear to play a key role in the pathogenesis of major depression and the therapeutic mechanisms of antidepressants. The firing rate of dorsal raphe serotonergic neurons is controlled by somatodendritic 5-hydroxytryptamine 1A (HTR1A) autoreceptors, and desensitization of these receptors is implicated in the antidepressant mechanism of selective serotonin reuptake inhibitors. We tested whether a functional polymorphism (C-1019G) in the promoter region of the HTR1A gene and serotonin-related genetic variants are related to fluoxetine antidepressant effect. We genotyped the HTR1A C-1019G polymorphism as well as polymorphisms in the serotonin transporter gene-linked polymorphic region (SERTPR), variable-number tandem-repeat polymorphisms in intron 2 (STin2) of the serotonin transporter gene, serotonin 2A receptor (T102C), tryptophan hydroxylase (A218C), and G-protein beta3 subunit (C825T) in 224 Chinese patients from southern Taiwan with major depression, who accepted 4-week fluoxetine treatment and therapeutic evaluation. Our results demonstrated that the HTR1A -1019C/C carriers (P=0.009) and SERTPR l/l carriers (P<0.001) showed a better response to fluoxetine, while other polymorphisms were not associated with fluoxetine therapeutic response. The major limitation of this study is the lack of a placebo control. Future prospective study with placebo control may help to predict and individualize antidepressant treatment.

Suggestive association between the C825T polymorphism of the G-protein beta3 subunit gene (GNB3) and clinical improvement with antipsychotics in schizophrenia

G-proteins are composed of alpha, beta and gamma subunits. Once activated, these subunits play a major role in the conversion of external receptor activation into intracellular signals. The functional C825T polymorphism of the beta3 subunit gene (GNB3) has recently been shown to modulate antidepressant response, with the T-allele conferring an increased signaling and being associated with favorable antidepressant response. We hypothesized that this polymorphism may be associated with response to antipsychotics in a population of 145 chronic schizophrenic patients deriving from two study-samples and being mainly treated with clozapine for up to 6 months. Overall, the C/C genotype was significantly associated with relative clinical improvement as measured by Brief Psychiatric Rating Scale (BPRS) change scores after 6 and 12 weeks (p<0.01 and p=0.03, respectively), with estimated effect sizes ranging from 4.8 to 7%. Our results further suggest that this effect is only attributable to Caucasians when compared to African-Americans. Moreover, our findings point to the role of intracellular mechanisms in antipsychotic response.

X-box binding protein 1 (XBP1) C−116G polymorphisms in bipolar disorders and age of onset

X-box binding protein 1 (XBP1), a critical gene in the endoplasmic reticulum stress response, is located on chromosome 22q12, which has been linked with bipolar disorders in several studies. Recently, associations have been reported between a polymorphism (-116C --> G) in the promoter region of XBP1, and bipolar disorders in both case-control study and family-based association study, however, this finding is not yet confirmed by other research using independent sample populations. To replicate this finding and determine the association between onset age of bipolar disorders and the XBP1 C--116G polymorphism, we investigated the prevalence of this polymorphism in a Chinese population (153 bipolar disorder patients and 174 controls). We were unable, however, to demonstrate a significant association between the C--116G polymorphism and bipolar disorders (P = 0.674 for genotype and P = 0.436 for allele frequency) or age at onset (P = 0.563). Further, no association was demonstrated between this polymorphism and family history in bipolar disorder patients. These negative findings suggest that the XBP1 C--116G polymorphism does not play a major role in the pathogenesis of bipolar disorders in Chinese populations.

Pharmacogenetics and bipolar disorder

Bipolar disorder (BD) is a major psychiatric condition that commonly requires prophylactic and episodic treatment. There is important variability in the therapeutic response and side-effect profiles to currently available pharmacological agents. Pharmacogenetics have provided new hopes to develop more efficient treatment strategies tailored to the individual patient's needs. This review assesses nonsystematically studies using pharmacogenetic strategies in BD. Most of these studies have focused on patients selected according to lithium response, and more recently, a growing number of studies have been investigating genetic factors in mixed samples of patients classified according to response to antidepressant treatment. Although previous clinical and family studies support the use of pharmacogenetic strategies both to increase phenotype homogeneity as well as to identify genetic factors that may mediate response to treatment, most molecular studies carried out to date are still preliminary and in need of external validation. A major problem has been comparability between studies, in part, because of differences in the criteria used to define response. More attention should be paid to standardize the criteria for drug response definition.

Seasonal affective disorder and the G-protein beta-3-subunit C825T polymorphism

BACKGROUND

Guanine nucleotide-binding proteins (G-proteins) have been implicated in affective disorders, with reports of altered signal transduction and G-protein levels. Association with seasonal affective disorder (SAD) has been found for the higher activity T-allele of the G-protein beta-3-subunit C825T polymorphism.

METHODS

European SAD patients (n = 159) and matched controls (n = 159) were genotyped for the C825T. Seasonality and diurnal preference were investigated in subsets of the material (n = 177 and 92, respectively).

RESULTS

We found no association between C825T and SAD (chi(2) =.09, p =.96) or seasonality (F = 1.76, p =.18). There was some evidence for an effect on diurnal preference but only in the control group (n = 46, t = -2.8, Bonferroni corrected p =.045).

CONCLUSIONS

These results suggest that the G-protein beta-3-subunit 825 T-allele does not play a major role in susceptibility to seasonal affective disorder in the population studied.

Association between a G-protein β3 subunit gene polymorphism and the symptomatology and treatment responses of major depressive disorders

The genes involved in signal transduction are major candidates in association studies on affective disorders and responses to antidepressants. We investigated whether the C825T polymorphism of the beta3 subunit of G protein (GNB3) gene is associated with the symptom severity or treatment response of major depressive disorders (MDDs) in a Korean sample of 106 MDD patients; our study also included 133 healthy controls. Hypertensive subjects were excluded from the study because association between GNB3 variants and hypertension has been reported in previous studies. We found significantly more carriers of the 825T allele in MDD patients than in normal controls (chi(2)=6.37, P=0.012; OR=2.19, 95% CI 1.18-4.05). The T-allele carriers showed higher scores than those with the CC genotype in the baseline total and in some subcategories of the Hamilton Depression Rating Scale (P<0.05). We also found a statistically significant association between T-allele carriers and antidepressant treatment response (P<0.05). These results suggest that the T allele of the C825T polymorphism in the GNB3 gene is associated with MDD. It was also demonstrated that MDD patients bearing the T allele had a severe symptomatology and a better response to antidepressant treatment than patients without the T allele.

C825T polymorphism in the G protein beta3-subunit gene is associated with seasonal affective disorder

BACKGROUND

Heterotrimeric G proteins play a pivotal role in the intracellular transduction of many transmitter-receptor interactions. Alterations in signal transduction and in G protein concentrations have been reported in seasonal and nonseasonal affective disorder. A single-nucleotide polymorphism (C825T) in the G protein beta3-subunit gene has been shown to influence intracellular response to G protein-coupled stimuli, and the T-allele of this polymorphism has been associated with hypertension and major depression.

METHODS

We genotyped deoxyribonucleic acid from peripheral mononuclear cells of 172 patients with seasonal affective disorder, winter type (SAD), and 143 healthy control subjects.

RESULTS

Patients with SAD were significantly more likely to be either homo- or heterozygous for the G(beta)3 T-allele when compared with healthy control subjects (p =.001), and they displayed a higher frequency of the G(beta)3 C825T T-allele (p =.021). The polymorphism was not associated with seasonality, which is the tendency to experience variations in mood and behavior with changing of the seasons.

CONCLUSIONS

The G(beta)3 C825T polymorphism was associated with SAD in our study sample. This finding strengthens the evidence for the involvement of G protein-coupled signal transduction in the pathogenesis of affective disorder.

Toward molecular diagnostics of mood disorders in psychiatry

Mental disorders are highly prevalent and often difficult to diagnose. There is a significant gap between advances in their pharmacotherapy and the present lack of objective biologic tests for diagnosis. The special complexity of diagnosis in psychiatry is related to the absence of objective diagnostic "gold standards", co-morbidity, heterogeneity and equifinality, quantitative trait loci, and locus heterogeneity. Here, we review recent findings relating to diagnostic, pathophysiological, and linkage markers for mood disorders at the biochemical level involving monoamine neurotransmitters, hormones, and signal-transducing G proteins. Identification of biological diagnostic markers could enable segregating mood disorders to several biologically different subtypes. New-era methods and strategies involving genomics, proteomics, multi-marker approach and single nucleotide polymorphisms have the potential to revolutionize future diagnosis in psychiatry.