G-Protein beta(3) subunit gene variant and left ventricular hypertrophy in essential hypertension

Single-Nucleotide Polymorphism in Genes Encoding G Protein Subunits GNB3 and GNAQ Increase the Risk of Cardiovascular Morbidity among Patients Undergoing Renal Replacement Therapy

Single-nucleotide polymorphisms in G protein subunits are linked to an increased risk of cardiovascular events among the general population. We assessed the effects of GNB3 c.825C > T, GNAQ -695/-694GC > TT, and GNAS c.393C > T polymorphisms on the risk of cardiovascular events among 454 patients undergoing renal replacement therapy. The patients were followed up for a median of 4.5 years after the initiation of dialysis. Carriers of the TT/TT genotype of GNAQ required stenting because of coronary artery stenosis (p = 0.0009) and developed cardiovascular events involving more than one organ system (p = 0.03) significantly earlier and more frequently than did the GC/TT or GC/GC genotypes. Multivariate analysis found that the TT/TT genotype of GNAQ was an independent risk factor for coronary artery stenosis requiring stent (hazard ratio, 4.5; p = 0.001), cardiovascular events (hazard ratio, 1.93; p = 0.04) and cardiovascular events affecting multiple organs (hazard ratio, 4.9; p = 0.03). In the subgroup of male patients left ventricular dilatation with abnormally increased LVEDD values occurred significantly more frequently in TT genotypes of GNB3 than in CT/CC genotypes (p = 0.007). Our findings suggest that male dialysis patients carrying the TT genotype of GNB3 are at higher risk of left ventricular dilatation and that dialysis patients carrying the TT/TT genotype of GNAQ are prone to coronary artery stenosis and severe cardiovascular events.

Association polymorphism of guanine nucleotide–binding protein β3 subunit (GNB3) C825T and insertion/deletion of the angiotensin-converting enzyme (ACE) gene with peripartum cardiomyopathy

Introduction

Peripartum cardiomyopathy (PPCM) is a potentially life-threatening pregnancy-related heart disease. Genetic roles such as gene polymorphisms may relate to the etiology of PPCM. This study analyzes the association between single nucleotide gene polymorphism (SNP) guanine nucleotide–binding protein beta-3 subunit (GNB3) C825T and insertion/deletion (I/D) of the angiotensin-converting enzyme (ACE) gene with the incidence of PPCM.

Methods

An analytic observational study with a case–control design was conducted at the Integrated Cardiac Service Center of Dr. Soetomo General Hospital, Surabaya, Indonesia. PPCM patients of the case and control groups were enrolled. Baseline characteristic data were collected and blood samples were analyzed for SNP in the GNB3 C825T gene and for I/D in the ACE gene by using the polymerase chain reaction, restriction fragment length polymorphism, and Sanger sequencing. We also assessed ACE levels among different ACE genotypes using a sandwich-ELISA test.

Results

A total of 100 patients were included in this study, with 34 PPCM cases and 66 controls. There were significant differences in GNB3 TT and TC genotypes in the case group compared with that in the control group (TT: 35.3% vs. 10.6%, p = 0.003; TC: 41.2% vs. 62.5%, p = 0.022). The TT genotype increased the risk of PPCM by 4.6-fold. There was also a significant difference in the ACE DD genotype in the case group compared with that in the control group (26.5% vs. 9.1%, p = 0.021). DD genotypes increased the risk of PPCM by 3.6-fold. ACE levels were significantly higher in the DD genotype group than in the ID and II genotype groups (4,356.88 ± 232.44 pg/mL vs. 3,980.91 ± 77.79 pg/mL vs. 3,679.94 ± 325.77 pg/mL, p < 0.001).

Conclusion

The TT genotype of GNB3 and the DD genotype of the ACE are likely to increase the risk of PPCM. Therefore, these polymorphisms may be predisposing risk factors for PPCM incidence. ACE levels were significantly higher in the DD genotype group, which certainly had clinical implications for the management of PPCM patients in the administration of ACE inhibitors as one of the therapy options.

GNB3 c.825C>T (rs5443) Polymorphism and Risk of Acute Cardiovascular Events after Renal Allograft Transplant

The c.825C>T single-nucleotide polymorphism (rs5443) of the guanine nucleotide-binding protein subunit β3 (GNB3) results in increased intracellular signal transduction via G-proteins. The present study investigated the effect of the GNB3 c.825C>T polymorphism on cardiovascular events among renal allograft recipients posttransplant. Our retrospective study involved 436 renal allograft recipients who were followed up for up to 8 years after transplant. The GNB3 c.825C>T polymorphism was detected with restriction fragment length polymorphism (RFLP) polymerase chain reaction (PCR). The GNB3 TT genotype was detected in 43 (10%) of 436 recipients. Death due to an acute cardiovascular event occurred more frequently among recipients with the TT genotype (4 [9%]) than among those with the CC/CT genotypes (7 [2%]; p = 0.003). The rates of myocardial infarction (MI)−free survival (p = 0.003) and acute peripheral artery occlusive disease (PAOD)−free survival (p = 0.004) were significantly lower among T-homozygous patients. A multivariate analysis showed that homozygous GNB3 c.825C>T polymorphism exerted only a mild effect for the occurrence of myocardial infarction (relative risk, 2.2; p = 0.065) or acute PAOD (relative risk, 2.4; p = 0.05) after renal transplant. Our results suggest that the homozygous GNB3 T allele exerts noticeable effects on the risk of MI and acute PAOD only in the presence of additional nonheritable risk factors.

The sirtuin1 gene associates with left ventricular myocardial hypertrophy and remodeling in two chronic kidney disease cohorts: a longitudinal study

BACKGROUND

Oxidative stress and inflammation are major drivers of myocardial hypertrophy in chronic kidney disease (CKD). The silent information regulator gene 1 (Sirt1) is a fundamental mediator of the response to oxidative stress and inflammation and promotes myocardial growth under stress conditions; therefore, it may contribute to myocardial hypertrophy and concentric remodeling of the left ventricle (LV) in CKD.

METHODS

We investigated the cross-sectional and longitudinal relationship between three candidate polymorphisms in the Sirt1 gene and LV parameters in two cohorts of CKD patients including 235 stage G5D patients and 179 stages G1-5 patients, respectively.

RESULTS

In both cohorts, the C allele of the Sirt1 rs7069102 polymorphism associated with the posterior wall thickness in separate and combined analyses (beta = 0.15, P = 2 × 10) but was unrelated with the LV volume and the LV mass index indicating a peculiar association of this allele with LV concentric remodeling. Accordingly, the same allele was linked with the LV mass-to-volume ratio in separate and combined (beta = 0.14, P = 2 × 10) analyses in the same cohorts. Furthermore, in longitudinal analyses patients harboring the C allele showed a more pronounced increase in LV mass-to-volume ratio over time than patients without such an allele (regression coefficient = 0.14, 95% confidence interval: 0.05-0.23; P = 3 × 10 in the combined analysis).

CONCLUSION

The rs7069102 polymorphism in the Sirt1 gene is associated with LV concentric remodeling in two independent cohorts of stages G5D and G1-5 CKD patients. These results offer a genetic basis to the hypothesis that the Sirt1 gene plays a causal role in myocardial hypertrophy and LV concentric remodeling in these patients.

Prediction of the Risk for Essential Hypertension among Carriers of C825T Genetic Polymorphism of G Protein β3 (GNB3) Gene

BACKGROUND

The guanine nucleotide-binding protein beta polypeptide 3 (GNB3) 825T allele encodes a product that enhances the activation of heterotrimeric G proteins, which is associated with the occurrence of the splice variant Gβ3 s that could play a role in vascular reactivity and hyperproliferation of smooth muscle cells, that makes such proteins attractive candidate gene products for susceptibility to essential hypertension (EH).

OBJECTIVE

To predict the risk for EH in individuals with C825T genetic polymorphism of G protein β3 gene.

METHODS

The study consisted of 222 normotensive individuals and 216 hypertensive patients. Individuals were genotyped for C825T genetic polymorphism of G protein β3 gene rs5443 by using restriction fragment length polymorphism.

RESULTS

Frequencies of C and T alleles were 58.1% and 41.9%, respectively, in the control group compared with 47.7% and 52.3%, respectively, in the hypertensive group. The carriers of rs5443 (T) allele exhibited a significant greater risk for EH compared with the carriers of rs5443 (C) allele (odds ratio = 1.5, 95% confidence interval = 1.2-2.0).

CONCLUSION

T allele is a risk factor for EH in the Egyptian population, which may be used as a prognostic and a therapeutic target of prophylaxis.

Does the GNB3 C825T Polymorphism Influence Swimming Performance in Competitive Swimmers?

Single nucleotide polymorphism C825T located within the GNB3 gene has been proposed in the literature as the performance enhancing polymorphism in highly trained athletes. Therefore, the aim of the present study was to verify the hypothesis assuming an association between the C825T polymorphic site and performance of competitive swimmers. The frequencies of C/T alleles and distribution of CC, CT and TT genotypes of the C825T GNB3 polymorphism were compared between athletes and nonathletic controls as well as between sprint and endurance swimmers. Genomic DNA was extracted from 197 competitive swimmers (50 long distance swimmers (LDS) and 147 short distance swimmers (SDS)) and 379 sedentary volunteers. The allele frequencies and genotype distribution of the C825T polymorphic site were not significantly different when LDS and SDS were compared to sedentary controls. Gender-specific analysis did not reveal any significant differences in allele and genotype distribution, neither between female controls and female swimmers nor between male controls and male swimmers. No significant differences in allele frequencies and genotype distribution were observed when LDS and SDS as well as groups of swimmers stratified by gender were compared. The results of this study do not support the hypothesis that the C825T polymorphism of the GNB3 gene is associated with swimming performance in competitive swimmers.

G-Protein β3-Subunit Gene C825T Polymorphism and Cardiovascular Risk: An Updated Review

Hypertension is a common disorder of multifactorial origin that constitutes a major risk factor for cardiovascular events such as stroke and myocardial infarction. The subunits of the heterotrimeric G proteins are attractive candidate gene products for susceptibility to hypertension, obesity and insulin resistance syndrome. A polymorphism (825C/T) in exon 10 of the GNB3 gene, encoding for the Gβ3 subunit, has been described. The 825T allele is associated with alternative splicing of the gene and formation of a truncated but functionally active β3 subunit. Many studies have investigated whether carriers of the 825T allele are at increased risk for hypertension, obesity, insulin-resistance and left ventricular hypertrophy with apparently conflicting results. The present review demonstrates that GNB3 825T allele is a useful genetic marker for better defining the risk profile of hypertensive patients, as it is associated with increased risk of stroke and myocardial infarction in longitudinal studies in Caucasians.

G-protein beta-3 subunit genotype predicts enhanced benefit of fixed-dose isosorbide dinitrate and hydralazine: results of A-HeFT

OBJECTIVES

The purpose of this study was to evaluate the influence of the guanine nucleotide-binding proteins (G-proteins), beta-3 subunit (GNB3) genotype on the effectiveness of a fixed-dose combination of isosorbide dinitrate and hydralazine (FDC I/H) in A-HeFT (African American Heart Failure Trial).

BACKGROUND

GNB3 plays a role in alpha2-adrenergic signaling. A polymorphism (C825T) exists, and the T allele is linked to enhanced alpha-adrenergic tone and is more prevalent in African Americans.

METHODS

A total of 350 subjects enrolled in the genetic substudy (GRAHF [Genetic Risk Assessment of Heart Failure in African Americans]) were genotyped for the C825T polymorphism. The impact of FDC I/H on a composite score (CS) that incorporated death, hospital stay for heart failure, and change in quality of life (QoL) and on event-free survival were assessed in GNB3 genotype subsets.

RESULTS

The GRAHF cohort was 60% male, 25% ischemic, 97% New York Heart Association functional class III, age 57 ± 13 years, with a mean qualifying left ventricular ejection fraction of 0.24 ± 0.06. For GNB3 genotype, 184 subjects were TT (53%), 137 (39%) CT, and 29 (8%) were CC. In GNB3 TT subjects, FDC I/H improved the CS (FDC I/H = 0.50 ± 1.6; placebo = -0.11 ± 1.8, p = 0.02), QoL (FDC I/H = 0.69 ± 1.4; placebo = 0.24 ± 1.5, p = 0.04), and event-free survival (hazard ratio: 0.51, p = 0.047), but not in subjects with the C allele (for CS, FDC I/H = -0.05 ± 1.7; placebo = -0.09 ± 1.7, p = 0.87; for QoL, FDC I/H = 0.28 ± 1.5; placebo = 0.14 ± 1.5, p = 0.56; and for event-free survival, p = 0.35).

CONCLUSIONS

The GNB3 TT genotype was associated with greater therapeutic effect of FDC I/H in A-HeFT. The role of the GNB3 genotype for targeting therapy with FDC I/H deserves further study.

Is gnb3 c825t polymorphism associated with elite status of polish athletes?

The GNB3 gene encodes the beta 3 subunit of heterotrimeric G-proteins that are key components of intracellular signal transduction between G protein-coupled receptors (GPCR) and intracellular effectors and might be considered as a potential candidate gene for physical performance.

OBJECTIVES

The aim of this study was to compare frequency distribution of the common C to T polymorphism at position 825 (C825T) of the GNB3 gene between athletes and nonathletic controls of the Polish population as well as to compare the genotype distribution and allele frequency of C825T variants within a group of athletes, i.e. between athletes of sports of different metabolic demands and competitive levels.

METHODS

The study was performed in a group of 223 Polish athletes of the highest nationally competitive standard (123 endurance-oriented athletes and 100 strength/ power athletes). Control samples were prepared from 354 unrelated, sedentary volunteers.

RESULTS

The χ(2) test revealed no statistical differences between the endurance-oriented athletes and the control group or between sprint/strength athletes and the control group across the GNB3 825C/T genotypes. There were no male-female genotype or allele frequency differences in controls or in either strength/power or endurance-oriented athletes. No statistically significant differences in either allele frequencies or genotype distribution were noted between the top-elite, elite or sub-elite of endurance-oriented and strength/power athletes and the control group.

CONCLUSIONS

No association between elite status of Polish athletes and the GNB3 C825T polymorphic site has been found.

Genetic variants predicting left ventricular hypertrophy in a diabetic population: a Go-DARTS study including meta-analysis

Background

Left ventricular hypertrophy has multiple aetiologies including diabetes and genetic factors. We aimed to identify genetic variants predicting left ventricular hypertrophy in diabetic individuals.

Methods

Demographic, echocardiographic, prescribing, morbidity, mortality and genotyping databases connected with the Genetics of Diabetes Audit and Research in Tayside, Scotland project were accurately linked using a patient-specific identifier. Left ventricular hypertrophy cases were identified using echocardiographic data.

Genotyping data from 973 cases and 1443 non-left ventricular hypertrophy controls were analysed, investigating whether single nucleotide polymorphisms associated with left ventricular hypertrophy in previous Genome Wide Association Studies predicted left ventricular hypertrophy in our population of individuals with type 2 diabetes. Meta-analysis assessed overall significance of these single nucleotide polymorphisms, which were also used to create gene scores. Logistic regression assessed whether these scores predicted left ventricular hypertrophy.

Results

Two single nucleotide polymorphisms previously associated with left ventricular hypertrophy were significant: rs17132261: OR 2.03, 95% CI 1.10-3.73, p-value 0.02 and rs2292462: OR 0.82, 95% CI 0.73-0.93 and p-value 2.26x10^-3. Meta-analysis confirmed rs17132261 and rs2292462 were associated with left ventricular hypertrophy (p=1.03x10^-8 and p=5.86x10^-10 respectively) and one single nucleotide polymorphisms in IGF1R (rs4966014) became genome wide significant upon meta-analysis although was not significant in our study. Gene scoring based on published single nucleotide polymorphisms also predicted left ventricular hypertrophy in our study.

Rs17132261, within SLC25A46, encodes a mitochondrial phosphate transporter, implying abnormal myocardial energetics contribute to left ventricular hypertrophy development. Rs2292462 lies within the obesity-implicated neuromedin B gene. Rs4966014 lies within the IGF1R1 gene. IGF1 signalling is an established factor in cardiac hypertrophy.

Conclusions

We created a resource to study genetics of left ventricular hypertrophy in diabetes and validated our left ventricular hypertrophy phenotype in replicating single nucleotide polymorphisms identified by previous genome wide association studies investigating left ventricular hypertrophy.

Association of GNB3 C825T polymorphism with plasma electrolyte balance and susceptibility to hypertension

The role of G-protein activation in cardiovascular disorders is well-known. G-protein β3 subunit (GNB3) C825T polymorphism is associated with increased intracellular signal transduction. We investigated the role of the variant in plasma sodium and potassium concentrations and association with hypertension. 345 healthy controls and 455 patients with essential hypertension were enrolled. Plasma renin activity and aldosterone concentration were measured. The variant, typed by SNaPshot, was analyzed on an ABI Prism 3100 Genetic Analyzer and GeneScan. The TT genotype and T allele were over-represented in the patients (p < 0.001, p < 0.0001). Multiple-logistic regression disclosed that the risk of hypertension was significantly greater for TT (p < 0.0001, OR = 6.1, CI = 2.9-12.7). One-way ANOVA revealed that hypertensive T-allele carriers (CT+TT), compared to non-carriers (CC), had a greater body mass index (BMI), mean arterial pressure (MAP) and PAC (p = 0.01, p = 0.01, p < 0.0001, respectively); while the patients with 825TT risk genotype showed higher plasma sodium and lower potassium (p < 0.0001, each). The results strongly emphasize, not only the role of C825T polymorphism by the induction of increased G-protein activity and enhancement of Na/h exchangers, but also the association with higher plasma sodium and lower potassium levels, high BMI and susceptibility to hypertension.

Novel quantitative trait locus is mapped to chromosome 12p11 for left ventricular mass in Dominican families: the Family Study of Stroke Risk and Carotid Atherosclerosis

Background

Left ventricular mass (LVM) is an important risk factor for stroke and vascular disease. The genetic basis of LVM is unclear although a high heritability has been suggested. We sought to map quantitative trait loci (QTL) for LVM using large Dominican families.

Methods

Probands were selected from Dominican subjects of the population-based Northern Manhattan Study (NOMAS). LVM was measured by transthoracic echocardiography. A set of 405 microsatellite markers was used to screen the whole genome among 1360 subjects from 100 Dominican families who had complete phenotype data and DNA available. A polygenic covariate screening was run to identify the significant covariates. Variance components analysis was used to estimate heritability and to detect evidence for linkage, after adjusting for significant risk factors. Ordered-subset Analysis (OSA) was conducted to identify a more homogeneous subset for stratification analysis.

Results

LVM had a heritability of 0.58 in the studied population (p < 0.0001). The most significant evidence for linkage was found at chromosome 12p11 (MLOD = 3.11, empirical p = 0.0003) with peak marker at D12S1042. This linkage was significantly increased in a subset of families with the high average waist circumference (MLOD = 4.45, p = 0.0045 for increase in evidence for linkage).

Conclusion

We mapped a novel QTL near D12S1042 for LVM in Dominicans. Enhanced linkage evidence in families with larger waist circumference suggests that gene(s) residing within the QTL interact(s) with abdominal obesity to contribute to phenotypic variation of LVM. Suggestive evidence for linkage (LOD = 1.99) has been reported at the same peak marker for left ventricular geometry in a White population from the HyperGEN study, underscoring the importance of this QTL for left ventricular phenotype. Further fine mapping and validation studies are warranted to identify the underpinning genes.

Genetic variants associated with cardiac structure and function: a meta-analysis and replication of genome-wide association data

CONTEXT

Echocardiographic measures of left ventricular (LV) structure and function are heritable phenotypes of cardiovascular disease.

OBJECTIVE

To identify common genetic variants associated with cardiac structure and function by conducting a meta-analysis of genome-wide association data in 5 population-based cohort studies (stage 1) with replication (stage 2) in 2 other community-based samples.

DESIGN, SETTING, AND PARTICIPANTS

Within each of 5 community-based cohorts comprising the EchoGen consortium (stage 1; n = 12 612 individuals of European ancestry; 55% women, aged 26-95 years; examinations between 1978-2008), we estimated the association between approximately 2.5 million single-nucleotide polymorphisms (SNPs; imputed to the HapMap CEU panel) and echocardiographic traits. In stage 2, SNPs significantly associated with traits in stage 1 were tested for association in 2 other cohorts (n = 4094 people of European ancestry). Using a prespecified P value threshold of 5 x 10(-7) to indicate genome-wide significance, we performed an inverse variance-weighted fixed-effects meta-analysis of genome-wide association data from each cohort.

MAIN OUTCOME MEASURES

Echocardiographic traits: LV mass, internal dimensions, wall thickness, systolic dysfunction, aortic root, and left atrial size.

RESULTS

In stage 1, 16 genetic loci were associated with 5 echocardiographic traits: 1 each with LV internal dimensions and systolic dysfunction, 3 each with LV mass and wall thickness, and 8 with aortic root size. In stage 2, 5 loci replicated (6q22 locus associated with LV diastolic dimensions, explaining <1% of trait variance; 5q23, 12p12, 12q14, and 17p13 associated with aortic root size, explaining 1%-3% of trait variance).

CONCLUSIONS

We identified 5 genetic loci harboring common variants that were associated with variation in LV diastolic dimensions and aortic root size, but such findings explained a very small proportion of variance. Further studies are required to replicate these findings, identify the causal variants at or near these loci, characterize their functional significance, and determine whether they are related to overt cardiovascular disease.

Change of genetic determinants of left ventricular structure in adolescence: longitudinal evidence from the Georgia cardiovascular twin study

BACKGROUND

Genetic contribution to left ventricular (LV) structure is generally recognized, but whether and how this influence varies by ethnicity or with age is unknown.

METHODS

Participants were 517 European-American (EA) and African-American (AA) twin pairs (mean age: 14.6 +/- 3.0) at visit 1 and 422 EA and AA twin pairs at follow-up 4.1 years later. Echocardiograms were obtained on both visits. Data were analyzed using the structural equation modeling software Mx.

RESULTS

Body mass index (BMI) was a strong predictor for all LV measures at both visits 1 and 2, accounting for 3.5-24.2% of the total variance. Hemodynamics explained up to 4.5% additional LV measures variance. After adjusting for BMI, LV measures showed substantial heritability (range: 21-71%). Best-fitting longitudinal models revealed considerable novel genetic effects on the interventricular septum, posterior wall-, and relative wall thickness (RWT) (but not LV internal diameter), accounting for 32-41% of the phenotypic variance at visit 2, with no significant gender and ethnic effects. There was a gender difference for LV mass index in AAs (P < 0.01), with a significant influence of novel genetic effects in males (47%), but not in females. No gender difference was seen in EAs, with 34% of the phenotypic variance at visit 2 attributable to novel genetic effects.

CONCLUSIONS

The heritability of cardiac structure and geometry was equally substantial in both AAs and EAs. Significant novel genetic influences were detected for all measures but LV inner diameter and LV mass index in AA females. Further developmental genetic studies are warranted to elucidate the nature of the emerging gene effects during the transition from adolescence to adulthood.

Genetics of arterial hypertension and hypotension

Human hypertension affects affects more than 20% of the adult population in industrialized countries, and it is implicated in millions of deaths worldwide each year from stroke, heart failure and ischemic heart disease. Available evidence suggests a major genetic impact on blood pressure regulation. Studies in monogenic hypertension revealed that renal salt and volume regulation systems are predominantly involved in the genesis of these disorders. Mutations here affect the synthesis of mineralocorticoids, the function of the mineralocorticoid receptor, epithelial sodium channels and their regulation by a new class of kinases, termed WNK kinases. It has been learned from monogenic hypotension that almost all ion transporters involved in the renal uptake of Na(+) have a major impact on blood pressure regulation. For essential hypertension as a complex disease, many candidate genes have been analysed. These include components of the renin-angiotensin-aldosterone system, adducin, beta-adrenoceptors, G protein subunits, regulators of G protein signalling (RGS) proteins, Rho kinases and G protein receptor kinases. At present, the individual impact of common polymorphisms in these genes on the observed blood pressure variation, on risk for stroke and as predictors of antihypertensive responses remains small and clinically irrelevant. Nevertheless, these studies have greatly augmented our knowledge on the regulation of renal functions, cellular signal transduction and the integration of both. Together, this provides the basis for the identification of novel drug targets and, hopefully, innovative antihypertensive drugs.

G-protein beta-3 subunit C825T polymorphism, sodium and arterial blood pressure: a community-based study of Japanese men and women

Epidemiological evidence on gene-environment effects of the G-protein beta-3 subunit C825T polymorphisms and sodium on blood pressure in the free-living general population is limited. We examined the associations between the C825T polymorphism and blood pressure levels, stratified by the sodium variables estimated by 24-h urinary sodium excretion and a dietary questionnaire, among 1,471 men and women aged 30-74 from a community in Japan. Our a priori hypothesis was that individuals with the 825T allele have elevated blood pressure among subjects with a high sodium intake. Among the whole group, the systolic blood pressure level was +2.2 mmHg (p = 0.10) higher in TT than CC genotype individuals after adjustment for sex, age, antihypertensive medication use, body mass index, and alcohol consumption. This difference was more evident among individuals with low sodium excretion (+4.5 mmHg, p = 0.01), low present sodium intake (+3.2 mmHg, p = 0.11), and low past sodium intake (+4.8 mmHg, p = 0.02). No associations were observed among those with high sodium variables. Our results indicate that the G-protein beta-3 subunit C825T polymorphism is associated with higher systolic blood pressure levels in a large free-living Japanese population, and more specifically in women with a low sodium intake. This finding helps to explain part of the discrepancy between the previously reported genetic association among different ethnic groups.

HYPERTENSION, OBESITY AND GNB3 GENE VARIANTS

The polymorphism C825T of the gene encoding the G-protein beta 3-subunit (GNB3) was found to be associated with an increased prevalence of hypertension in a number of studies. The aim of the present study was to investigate the association between this polymorphism and blood pressure phenotypes in an urban, large and ethnically mixed population of Brazil. 2. Individuals (n=1,568) were randomly selected from the general population of the Vitória City metropolitan area. The GNB3 C825T polymorphism was genotyped in each individual. Baseline cardiovascular risk factors were collected for all participants. Cardiovascular risk variables and genotypes were compared using anova and the Chi-squared test for univariate comparisons and logistic regression for multiple comparisons. 3. A statistically significant interaction between the 825T allele and obesity was observed for systolic blood pressure (SBP; P=0.02). In fact, the C825T genotype was predictive of SBP only in individuals with increased body mass index (P=0.02). In addition, in a multiple logistic regression model conducted in the obese population and adjusted for age, sex, ethnicity, diabetes, triglycerides and total cholesterol, the presence of the T allele was significantly associated with a 1.5-fold (95% confidence interval 1.04--2.26) increased risk of hypertension. Lack of statistical power does not explain the absence of other positive gene-environment interactions. 4. The present results suggest that an important gene yen environment interaction may take place between bodyweight regulation and the GNB3 gene. This finding provides further evidence for a role of the 825T allele in hypertension susceptibility and may be used for better disease stratification.

G-protein beta-3 subunit gene C825 T polymorphism: Influence on plasma sodium and potassium concentrations in essential hypertensive patients

The C825T polymorphism of the beta-3 subunit of the protein G (GNB3) has been related to an increased activity of the Na+/H+ exchanger (NHE-1) through the synthesis of an anomalous hyperactive protein. Because of the important role of this system in essential hypertension (EH), we analysed the distribution of the different genotypes of this polymorphism in normotensive subjects (NS) and essential hypertensive patients (EHP), their relationship with the condition of salt sensitivity, plasma sodium and potassium concentrations and plasma renin activity (PRA) in EHP. 144 subjects (78 EHP and 76 NS) were studied. Salt sensitivity was assessed by the rapid protocol of Weinberger and genotype determination for GNB3 C825T polymorphism was performed by PCR. The distribution of the different genotypes was similar among EHP (CC 37.2%; CT 41.1%; TT 16.7%) and NS (CC 32.9%; CT 55.3%; TT 11.8%). In regard to general characteristics of EHP (including blood pressure levels) and the condition of salt sensitivity, there were no differences among the different genotypes. Plasma sodium concentration was higher and plasma potassium was lower in TT patients (141.0+/-1.7 and 3.7+/-0.1) than in CC patients (139.1+/-1.9 and 4.0+/-0.3) p<0.05. CT patients had intermediate values (139.9+/-1.9 and 3.9+/-0.2). PRA values were similar in the three genotypes as were the rest of analytical parameters studied. Our data demonstrate an association between the C825T polymorphism of the GNB3 and plasma sodium and potassium concentrations in EHP, as expression of an increase in NHE-1 activity, without modifications in PRA nor relationship with salt sensitivity.

Hypertensive heart disease

Left ventricular hypertrophy (LVH) and diastolic dysfunction (CHF-D) are the early manifestations of cardiovascular target organ damage in patients with arterial hypertension and signify hypertensive heart disease. Identification of hypertensive heart disease is critical, as these individuals are more prone to congestive heart failure, arrhythmias, myocardial infarction and sudden cardiac death. Regression of left ventricular (LV) mass with antihypertensive therapy decreases the risk of future cardiovascular events. The goal of antihypertensive therapy is to both lower blood pressure (BP) and interrupt BP-independent pathophysiologic processes that promote LVH and CHF-D. The purpose of this review is to summarize current and emerging approaches to the pathophysiology and treatment of hypertensive heart disease.

Association between the GNB3 Polymorphism and Blood Pressure in Young Korean Men

PURPOSE

The purpose of the current study was to investigate the associations between the GNB3 C825T polymorphism, body fatness and fitness, and blood pressure in a sample of young Korean men.

METHODS

A total of 282 apparently healthy Korean men (nonobese N = 152, obese N = 130) aged 19-33 yr participated in the study. Body fatness and blood pressure were measured by using standardized protocols. The GNB3 C825T was genotyped by using polymerase chain reaction with restriction fragment length polymorphism.

RESULTS

Univariate analyses of variance and Bonferroni post hoc tests showed that in the obese group only, TT homozygotes had a lower VO2max (P = 0.015 and 0.043, respectively) but higher resting systolic (P = 0.025 and < 0.001, respectively) and mean arterial blood pressures (P = 0.049 and 0.002, respectively) than CC homozygotes or CT heterozygotes. We further investigated possible interactions between group and genotype and found a significant interaction in SBP only (P = 0.037) between the group and genotype, even when controlling for age, BMI, and VO2max as potential confounding factors. Stepwise regression analyses showed that body mass index and GNB3 genotype were two independent predictors for the variations in systolic blood pressure and heart rate up to by 14.3 and 14.5%, respectively. In addition, waist-to-hip ratio explained an individual variation in mean arterial pressure (MAP) up to by 11.2%.

CONCLUSION

The current findings of the study suggest that increased body fatness along with low cardiorespiratory fitness may magnify the genetic susceptibility of the GNB3 825T allele to elevated blood pressure in this study population.

The 825C/T polymorphism of G-protein beta3 subunit gene and risk of ischaemic stroke

In this study, we investigated the association of G protein beta3 subunit gene (GNB 3) C825T polymorphism with ischaemic stroke and its subtypes in the Chinese Han population in a large case-control study. A total of 990 ischemic stroke patients and 1124 controls were recruited from six medical centres in China. Genotype was determined by polymerase chain reaction and restriction fragment length polymorphism (RFLP) assay. Logistic regression analysis was performed to identify the independent risk factors for stroke. The frequency of 825T carriers is significantly higher in cerebral thrombosis in male subjects (OR=1.35, 95% CI, 1.01-1.82, P=0.046). After further adjustment with traditional risk factors to stroke, the association is not significant. In conclusion, the GNB3 825T allele is not an independent risk factor to ischaemic stroke in the Chinese population.

Genetic polymorphisms and heart failure

Heart failure is a complex clinical syndrome. There is evidence for a genetic contribution to the pathophysiology of heart failure. Considering the fundamental role of neurohormonal factors in the pathophysiology and progression of cardiac dysfunction and hypertrophy, variants of genes involved in this system are logical candidate genes in heart failure. In this report, genetic polymorphisms of the major neurohormonal systems in heart failure will be discussed. Studies on polymorphisms of the renin-angiotensin-aldosterone system (RAAS), adrenergic receptor polymorphisms, endothelin (receptor) polymorphisms, and a group of miscellaneous polymorphisms that may be involved in the development or phenotypic expression of heart failure will be reviewed. Research on left ventricular hypertrophy is also included. The majority of genetic association studies focused on the ACE I/D polymorphism. Initial genetic associations have often been difficult to replicate, mainly due to problems in study design and lack of power. Promising results have been obtained with genetic polymorphisms of the RAAS and sympathetic system. Considering the evidence so far, a modifying role for these polymorphisms seems more likely than a role of these variants as susceptibility genes. Besides the need for larger studies to examine the effects of single nucleotide polymorphisms and haplotypes, future studies also need to focus on the complexity of these systems and study gene-gene interactions and gene-environment interactions.

DNA polymorphisms in the tyrosine hydroxylase and GNB3 genes: association with unexpected death from acute myocardial infarction and increased heart weight

Sudden and unexpected death from myocardial infarction (MI) is one of the most commonly observed findings in forensic medicine. To investigate the biochemical and genetic background of this disease we investigated the genotypes for two polymorphisms associated with hypertension: TH01, a tetrameric microsatellite in the tyrosine hydroxylase gene and the single nucleotide polymorphism C825T in the GNB3 gene in 116 sudden deaths from MI (78 males, 38 females) and in a control group of 137 deaths from natural causes other than MI (52 males, 85 females). For TH01 no correlation with the prevalence of MI was found. For C825T, results were different. While for the male individuals allelic frequencies and genotype distributions were similar in both groups, T-homozygosity was significantly more common in female fatalities from MI than in the female control group (24% versus 7%; Relative Risk 2.29). Nevertheless, neither for TH01 nor for C825T an association with heart weight was found. Thus our results demonstrate that the C825T polymorphism may play a role in the development of myocardial infarctions, at least in females. They also demonstrate that the genetic component in complex diseases like MI may depend on the gender of the patients. As the influence of this polymorphism on arterial blood pressure appears to be relatively small, and G-proteins are involved in numerous intracellular signal cascades it can be speculated that T-homozygosity at this locus might influence the incidence or mortality of cardiovascular disease via hitherto unknown mechanisms.

C825T polymorphism of the G-protein beta3 subunit gene and atrial fibrillation: association of the TT genotype with a reduced risk for atrial fibrillation

BACKGROUND

A polymorphism consisting of a C825T substitution in the G-protein beta(3) subunit gene (GNB3) has been associated with enhanced human atrial inward rectifier potassium currents regarding the TT genotype. Therefore, we investigated a possible impact of the GNB3 C825T polymorphism on atrial fibrillation in an association study.

METHODS

Two hundred ninety-one consecutive patients admitted to our center with atrial fibrillation (age, 58 +/- 10 years) and 292 consecutive control patients without atrial tachyarrhythmias (59 +/- 11 years) were genotyped for the C825T polymorphism. Patients with coronary heart disease, valvular heart disease, or cardiomyopathy were excluded from the study. Both patient groups had a similar incidence of cardiovascular risk factors (hypertension, hypercholesterolemia, body mass index).

RESULTS

The prevalence of the GNB3 TT genotype was significantly lower in patients with atrial fibrillation (5.8%) than in the control group (12.0%); however, no significant differences in the frequencies of the CT and CC genotypes were found. The TT genotype was associated with a 54% decrease in the adjusted risk (OR from a multivariant model, 0.46; 95% CI, 0.24 to 0.87; P =.02) for the occurrence of atrial fibrillation.

CONCLUSIONS

The current study suggests an association between the GNB3 TT genotype and a reduced risk for the occurrence of atrial fibrillation.

G protein β3 subunit C825T polymorphism in primary IgA nephropathy

BACKGROUND

The T allele of the G protein beta3 subunit (GNB3) C825T polymorphism has been associated with increased signal transduction, increased activity of the kidney Na+/H+ exchanger, and also with late-onset essential hypertension. Hypertension is a strong independent risk factor for progression in IgA nephropathy (IgAN).

METHODS

We have studied this polymorphism in a regularly followed cohort of 299 biopsy-proven incident cases of IgAN, collected from 1989 to 1999 [208 males (70%)] and compared the genotypes and alleles distributions to 303 local Caucasian controls matched for the male predominance (214 males). The technique used was a polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) with BseDI as restriction enzyme and specific primers, followed by gel electrophoresis.

RESULTS

The TT, CT, and CC genotype frequencies were 13.7%, 45.8%, and 40.5% in IgAN, respectively, versus 7.6%, 47.2%, and 45.2% in controls, respectively (chi(2)= 6.16; P= 0.05). The excess of TT patients versus non-TT was significant in IgAN versus controls (chi(2)= 5.94; P= 0.015). The T allele frequency was 0.366 in IgAN versus 0.312 in controls (chi(2)= 3.97; P= 0.05). This data indicated that this polymorphism had a significant but mild influence on the occurrence/initiation of IgAN (RR = 1.81; 95% CI 1.07-3.07). In contrast, we could not demonstrate any significant and sustained difference in the clinical presentation and evolution of the homozygous TT patients compared to non-TT patients (CC + CT) despite a mean and median follow-up about 10 years. The progression to arterial hypertension or to chronic renal failure or to end-stage renal failure (ESRF) was not significantly different. In addition, multivariate Cox regression analysis excluded a significant independent role of C825T polymorphism on progression.

CONCLUSION

The C825T GNB3 polymorphism had a mild influence on occurrence/initiation of IgAN, but played no significant role in the progression of the disease.

Ambulatory blood pressure and left ventricular structure and function in relation to the G-protein beta3-subunit polymorphism C825T in White Europeans

The 825T allele of the G-protein beta(3)-subunit is associated with increased intracellular signalling. Its association with hypertension is inconsistent. We, therefore, studied the C825T polymorphism in relation to ambulatory blood pressure as well as left ventricular structure and function in two European populations. We genotyped 248 parents and 318 offspring, enrolled in the European Project on Genes in Hypertension in Cracow, Poland (n=286) and in Novosibirsk, Russian Federation (n=280). The 24-h ambulatory blood pressure was recorded using oscillometric SpaceLabs 90207 monitors. Within each centre, a single observer performed two-dimensionally guided M-mode echocardiography and Doppler sonography to measure left ventricular structure (American Society of Echocardiography conventions) and diastolic function: early (E) and late (A) peak diastolic inflow velocities. We used analysis of covariance and generalized estimating equations to allow for covariables and nonindependence among related subjects. Genotype frequencies were similar (P=0.25) in Cracow and Novosibirsk and amounted to 44.7% for CC, 47.2% for CT, and 8.1% for TT. Among parents (mean age: 51.3 years)-but not among offspring (mean age 25.1 years)-24-h, daytime and night time systolic blood pressures were 5-6 mmHg higher in TT homozygotes than in C allele carriers. In TT homozygous parents (-8.2 cm/sec, P=0.004) as well as in TT homozygous offspring (-7.5 cm/sec, P=0.02), the E-wave was significantly reduced, which in offspring also resulted in a lower E/A ratio (-0.25, P=0.002). Neither in parents nor in offspring, left ventricular mass index was associated with the C825T polymorphism. In conclusion, in TT homozygotes of both generations, early left ventricular relaxation was reduced. In TT homozygous parents, the latter observation might be because of the higher systolic pressure associated with the TT genotype.

Interaction of Gbeta3s, a splice variant of the G-protein Gbeta3, with Ggamma- and Galpha-proteins

The T-allele of a polymorphism (C825T) in the gene of the G-protein beta3-subunit is associated with a complex phenotype (hypertension, obesity, altered drug responses) and the occurrence of a splice variant termed Gbeta3s which lacks one of the seven WD-domains that compose Gbeta-proteins. Here, we analysed Gbetagamma dimer formation and Galpha activation by Gbeta3s, key functional characteristics of Gbeta-proteins. Cleavage protection assays frequently used to analyse Gbeta1gamma and Gbeta2gamma dimer formation failed for Gbeta3 and Gbeta3s, while in coprecipitation assays, dimerization of Gbeta3 and Gbeta3s with Ggamma5, Ggamma8(c) and Ggamma12 could be demonstrated. Upon expression of Gbeta3s in COS-7 and Sf9 insect cells, binding of GTPgammaS to Galpha-proteins induced by mastoparan-7 and the M(2) muscarinic acetylcholine receptor was facilitated in comparison with cells overexpressing wildtype Gbeta3, as indicated by twofold reduced agonist EC(50) values. Together, these results indicate that Gbeta3s is a biologically active Gbeta-protein that may mediate the enhanced signal transduction observed in cells with the 825T-allele.

A splice variant of the G protein beta 3-subunit implicated in disease states does not modulate ion channels

A single-nucleotide polymorphism (C825T) in the GNB3 gene produces an alternative splice variant of the heterotrimeric G protein beta3 subunit (Gbeta3). Translation of the alternatively spliced mRNA results in a protein product, Gbeta3-s, in which 41 amino acids are deleted from Gbeta3. Interestingly, previous studies indicate that the C825T allele occurs with a high frequency in patients with certain vascular disorders. However, little information is available regarding the functional role Gbeta3-s might play in ion channel modulation. To examine this aspect, Gbeta3 or Gbeta3-s, along with either Ggamma2 or Ggamma5, were expressed in rat sympathetic neurons by nuclear microinjection of vector encoding the desired protein. In contrast to Gbeta3, expression of Gbeta3-s did not modulate N-type Ca(2+) or G protein-gated inwardly rectifying K(+) channels. In addition, Gbeta3-s did not appear to complex with a pertussis toxin-insensitive mutant of Galpha(i2) or couple to natively expressed alpha(2)-adrenergic receptors. Finally, fluorescence resonance energy transfer (FRET) measurements indicated that enhanced yellow fluorescent protein (EYFP)-labeled Gbeta3-s does not form a Gbetagamma heterodimer when coexpressed with enhanced cyan fluorescent protein (ECFP)-labeled Ggamma2. Therefore, when expressed in sympathetic neurons, Gbeta3-s appears to lack biological activity--hence pathological conditions in patients carrying the homozygous C825T allele may result from a functional knockout of Gbeta3.

Characterization of the splice variant Gbeta3v of the human G-protein Gbeta3 subunit

A polymorphism (C825T) in the gene of the G-protein Gbeta3 (GNB3) has been the subject of numerous studies which have shown that the 825T-allele is associated with several cardiovascular and metabolic disorders. Furthermore, the T-allele is associated with the occurrence of the splice variant Gbeta3s which has been implicated in the pathogenesis of these disorders. Here, we characterise a novel splice variant of GNB3, termed Gbeta3v, which is generated by alternative splicing of parts from intron 9 as a novel exon 10a. Gbeta proteins belong to the superfamily of propeller proteins composed of seven regular WD-domains. In Gbeta3v, four of these WD-domains are retained but the protein has a novel C terminus. Gbeta3v forms dimers with Ggamma3 and Ggamma12 but these Gbetagamma complexes do not stimulate phospholipase C-beta2. Thus, a physiological role of Gbeta3v remains to be established. Gbeta3v transcripts are detectable in a wide variety of cells and tissues including fibroblasts, B lymphoblasts, retinoblastoma cells, retina, brain, umbilical cord and colon. However, there is no association with an allele of the GNB3 C825T polymorphism, which suggests that Gbeta3v does not contribute to the complex phenotype observed in association with the 825T-allele.

An epidemiological study of blood pressure and metabolic phenotypes in relation to the Gbeta3 C825T polymorphism

BACKGROUND

The 825T allele of the G-protein beta(3)-subunit gene is associated with increased intracellular signalling and adipogenesis in experimental studies. We studied the C825T polymorphism in relation to blood pressure, obesity and intermediate phenotypes in a Caucasian population.

METHODS

We genotyped 737 men and 775 women (participation rate, 64.3%) enrolled in a Belgian population study. Dichotomous phenotypes were tested for association with the C825T polymorphism by Fisher's exact test and multiple logistic regression. For continuous traits, we used analysis of covariance and generalized estimating equations.

RESULTS

The T allele (39.7 versus 29.1%) and TT genotype (16.1 versus 7.7%) were more prevalent in obese men than in non-obese men (P < or = 0.01). TT homozygous men, compared with C allele carriers, had higher daytime ambulatory blood pressure (mean systolic/diastolic differences, 3.6/2.5 mmHg; P < or = 0.02), higher body weight (2.7 kg, P = 0.04), greater risk of obesity (risk ratio, 1.90; P = 0.005), increased triceps skinfold thickness (2.3 mm, P = 0.007), higher serum insulin concentration (4.1 mU/l, P = 0.006), more insulin resistance (P = 0.01), and increased erythrocyte count (0.11 x 1012 cells/l, P = 0.04) and haematocrit (0.9%, P = 0.02). In women, haematocrit and erythrocyte count were also higher (P < or = 0.03) in T allele carriers, but other phenotypes were not correlated with the C825T polymorphism.

CONCLUSION

Male and female carriers of the T allele at position 825 of the G-protein beta(3)-subunit gene have a slightly higher haematocrit and erythrocyte count. Male TT homozygotes have a higher blood pressure and are more obese and insulin-resistant than C allele carriers. We speculate that the higher blood pressure in TT homozygous men might arise via a metabolic pathway characterized by obesity and insulin resistance as well as via increased peripheral resistance secondary to the higher haematocrit.

Identification and characterization of G beta 3s2, a novel splice variant of the G-protein beta 3 subunit

The T-allele of a polymorphism (C825T) in the gene for the G-protein beta 3 subunit (GNB3) is associated with cardiovascular and metabolic disorders, distinct cellular features and altered drug responses. The molecular mechanisms that give rise to this complex phenotype have been linked to the occurrence of G beta 3s, a splice variant of GNB3. G beta 3s is predominantly expressed in cells with the 825T-allele. In the present study we describe the identification and characterization of an additional G beta 3 splice variant referred to as G beta 3s2. Its mRNA is expressed in heart, blood cells and tumour tissue, and its expression is also tightly associated with the GNB3 825T-allele. G beta 3s2 is generated by alternative splicing using non-canonical splice sites. G beta subunits belong to the family of propeller proteins and consist of seven regular propeller blades. Transcripts for G beta 3s2 are lacking 129 bp of the coding sequence of the wild-type G beta 3 protein. Thus the predicted structure consists of only six propeller blades, which resembles the structure of G beta 3s. Co-immunoprecipitation analyses indicated that G beta 3s2 dimerizes with different G gamma subunits, e.g. G gamma 5, G gamma 8(C) and G gamma 12. In Sf9 insect cells, expression of G beta 3s2 together with G gamma 12 enhances receptor-stimulated activation of G alpha(i2). Expression of G beta 3s2 in mammalian cells activated the mitogen-activated protein kinase cascade. Together, these results suggest that G beta 3s2 is a biologically active G beta variant which may play a role in the manifestation of the complex phenotype associated with the 825T-allele.

G-protein beta3 subunit 825T allele and hypertension

The G-protein beta3 subunit (GNB3) C825T polymorphism was detected through a classical candidate gene approach using cell lines with enhanced G-protein activation from patients with essential hypertension. The 825T allele is associated with the expression of a shortened, functionally active splice variant of the G-protein beta3 subunit and enhanced intracellular signal transduction. Independent studies have confirmed an association of the 825T allele with hypertension in whites. Potential pathogenetic mechanisms comprise an increased susceptibility for obesity in 825T allele carriers and, potentially, increased responsiveness to vasoactive hormones. Both phenomena appear to be strongly influenced by lifestyle in the sense of a gene-environment interaction. Whether hypertensive 825T allele carriers are at increased risk for stroke and left ventricular hypertrophy remains controversial. Current studies try to define optimal therapy strategies for hypertensive 825T allele carriers.

Association of the G protein beta3 subunit T allele with insulin resistance in essential hypertension

A polymorphism (C825T) in the gene encoding the G protein beta3 subunit (GNB3) has recently been associated with hypertension and obesity in several populations. The aim of the study was to analyse the relationship between this polymorphism and insulin sensitivity, an hypothesised unifying factor for hypertension and obesity. One hundred thirty unrelated patients with essential hypertension, 70 female and 60 male, aged 58 +/- 1 years with systolic blood pressure of 173 +/- 2 mm Hg and diastolic blood pressure of 105 +/- 1 mm Hg, were genotyped for the GNB3 polymorphism by PCR and restriction digestion with BseDI, and classified in two groups according to the genotypes CC and CT + TT. Body mass index (BMI) was significantly higher in patients with the T allele as compared with patients without the T allele (29.3 +/- 0.4 vs. 26.7 +/- 0.6 kg/m2, p<0.001). On the contrary, there were no differences in the level of systolic or diastolic blood pressure among the genotypes. Insulin sensitivity was measured in a subgroup of 35 patients by means of an euglycemic hyperinsulinemic clamp test. In this subgroup, patients with the T allele displayed lower insulin sensitivity index (1.6 +/- 0.3 vs. 2.7 +/- 0.3 mg/kg/min, p = 0.022), higher fasting serum insulin (121 +/- 16 vs. 77 +/- 11 pmol/L, p = 0.032), higher serum glucose 120 min after 75 g load (9.8 +/- 1.2 vs. 7.0 +/- 0.5 mmol/L, p = 0.038), and higher glycosilated haemoglobin (5.7 +/- 0.4 vs. 4.7 +/- 0.2%; p = 0.042) as compared with patients without the T allele. A regression analysis showed that the association between the T allele and insulin sensitivity was independent of BMI (beta coefficient -0.386, p = 0.022). These results suggest a relationship between the 825T allele of GNB3 and insulin resistance in the essential hypertensive patients studied, which seems to be independent of BMI.

Identification and ethnic distribution of major haplotypes in the gene GNB3 encoding the G-protein beta3 subunit

The 825T-allele of the gene GNB3 encoding the G protein beta3 subunit is associated with hypertension and obesity, and identifies individuals highly responsive to diuretic therapy. Gbeta3s, a Gbeta3 protein variant generated by alternative splicing in carriers of the 825T-allele, is linked to increased signal transduction and is a potential cause for the observed pathophysiology. Here, we searched the entire GNB3 gene for additional polymorphisms and analysed their prevalence in Caucasian, black African and Asian populations. We detected six novel single nucleotide polymorphisms which were termed according to their location as G76A, G1906T, G2906A, A3882C, G5177A, and G5249A. Furthermore, we found a CACA-insertion-deletion polymorphism at position 6496. Genotyping and association studies resulted in the definition of two major GNB3 haplotypes, termed 'C-haplotype' (alleles 825C, 3882A, 5249G, 6496CACA-) and 'T-haplotype' (alleles 825T, 3882C, 5249A, 6496CACA+). Molecular modelling studies revealed that the pre-mRNA structures of both haplotypes exhibit marked differences which may account for the alternative splicing predominantly observed with the T-haplotype. The prevalence of these haplotypes in major ethnic populations differs considerably. Furthermore, we detected additional frequent GNB3 polymorphisms. These variants were restricted to one or two major ethnic populations. Our results will aid future studies on population-specific effects of the GNB3 variants on risk and course of frequent diseases, including hypertension, obesity, stroke and myocardial infarction. Furthermore, they will contribute to the understanding of GNB3-related population-specific pharmacogenetic differences in the response to major drugs, as already shown for diuretics and antidepressants.

Polymorphisms of genes encoding components of the sympathetic nervous system but not the renin-angiotensin system as risk factors for orthostatic hypotension

OBJECTIVE

The genetic background of orthostatic hypotension, an important risk factor for future cardiovascular morbidity and mortality, was investigated.

DESIGN AND METHODS

The study subjects comprised 415 community-dwelling individuals, who were free from any cardiovascular complications, aged 50 years or older (mean age 70.5 +/- 9 years). Basal systolic blood pressure (SBP) was measured twice in supine posture after resting for more than 10 min. The orthostatic change in SBP was determined at 1 min and 3 min after standing up. The maximum change in SBP after standing was determined. Orthostatic hypotension was defined as a decline in SBP greater than 20 mmHg. The polymorphisms of genes encoding components of the renin-angiotensin system and sympathetic nervous system, which play pivotal roles in postural change in blood pressure regulation, were determined.

RESULTS

There were no significant associations between the maximum change in SBP, the prevalence of orthostatic hypotension and gene polymorphisms of angiotensin-converting enzyme I/D, angiotensinogen M235T and angiotensin II type 1 receptor A1166C. On the contrary, polymorphism of the Gs protein alpha-subunit (GNAS1) T131C was significantly associated with the maximum change in SBP after standing [1.9 +/- 16 versus -3.6 +/- 16 mmHg (TT + TC versus CC), P = 0.008]. The prevalence of orthostatic hypotension was significantly different among GNAS1 genotypes (chi squared = 10.12, P = 0.011) and G-protein beta 3 subunit (GNB3) genotypes (chi squared = 6.12, P = 0.020). Multiple logistic regression analysis showed that both GNAS1 CC genotype [odds ratio (OR) = 2.79, 95% confidence interval (CI) 1.35-5.79, P = 0.006] and GNB3 C allele (OR = 1.78, 95% CI 1.06-3.00, P = 0.030) were independent risks for orthostatic hypotension.

CONCLUSIONS

These findings indicate that genes encoding sympathetic nervous components could be involved in the predisposition for orthostatic hypotension.

G protein beta 3 polymorphism and hemodynamic and body composition phenotypes in the HERITAGE Family Study

A C825T polymorphism of the G protein beta3 (GNB3) gene has been reported to be associated with hypertension and obesity. We analyzed the associations between the GNB3 C825T polymorphism and hemodynamic and body composition phenotypes in the sedentary state and their responses to endurance training in mainly normotensive white (n = 473) and black (n = 255) men and women. Blood pressure (BP) and heart rate (HR) were measured at rest and during submaximal exercise at constant power output (50 W), and stroke volume and cardiac output were obtained during exercise. Body composition was assessed with underwater weighing. Baseline systolic BP (SBP) at 50 W was slightly higher in the white CC homozygotes (P = 0.036), whereas in blacks the CC genotype was associated with a lower resting HR (P = 0.012). In blacks, the CC homozygotes showed a greater training-induced reduction in HR at 50 W (P = 0.013) and a similar trend was observed also in whites (P = 0.053). Black women carrying the CC genotype showed significantly greater reductions in resting SBP and diastolic BP (DBP) than the TT homozygotes, whereas in black men the changes in resting BP were similar across the genotypes (P < 0.05 for sex-by-GNB3 interactions). The GNB3 genotype was not associated with baseline body composition in blacks or whites. In blacks, the TT genotype was associated with a greater training-induced decrease in fat mass (P = 0.012) and percent body fat (P = 0.006). These data suggest that DNA sequence variation in the GNB3 locus is not a major modifier of endurance training-induced changes in hemodynamic and body composition phenotypes in healthy but previously sedentary subjects. The GNB3 genotype may play a minor role in HR and body fatness regulation in blacks and in responsiveness of resting BP to endurance training in black women.

G-protein beta3 subunit C825T polymorphism: no association with risk for hypertension and obesity

OBJECTIVE

Several recent studies have indicated that a C825T polymorphism in the gene encoding the G-protein beta3 subunit is a significant risk factor for hypertension and obesity. In this study, we tested whether this polymorphism is associated with hypertension and obesity in white men.

DESIGN

Population-based prospective cohort study.

METHODS

We followed a cohort of 903 men, aged 42-61 years at baseline, for an average time of 4.2 years. Genotyping was performed by polymerase chain reaction.

RESULTS

The genotype distribution was in Hardy-Weinberg equilibrium: 514 (57%) had the CC genotype, 49 (5%) had the TT genotype and 340 (38%) were heterozygous (T:C = 0.24:0.76). There was no statistically significant difference between the genotype groups in respect to baseline and end of follow-up risk for hypertension or obesity, systolic or diastolic blood pressure, or body mass index.

CONCLUSION

We conclude that the C825T polymorphism of the G-protein beta3 subunit gene does not notably contribute to the development of hypertension or obesity, and is not a significant determinant for blood pressure and body mass index in white men.

An association study of five genetic loci and left ventricular hypertrophy amongst Gulf Arabs

We carried out an association (case-control) study of five candidate genes--G-protein beta3 subunit gene variant; methylene tetrahydrofolate reductase (MTHFR); angiotensin converting enzyme (ACE) gene; and paraoxonase 1 and 2 (PON 1 and 2) genes--in a United Arab Emirati population. The aim was to establish a possible relationship between these five candidate genes and clinical left ventricular hypertrophy (LVH) in a genetically homogenous group. DNA samples were collected from 213 unrelated Nationals who were further segregated into 98 subjects with LVH (78 hypertensives and 20 normotensives) and 115 (23 hypertensives and 92 normotensives) age- and sex-matched controls who did not present with LVH. Of the five candidate gene markers studied, no significant differences in the genotype distribution of the MTHFR, PON 1 and 2 or ACE markers were found between the LVH and non-LVH groups. However, a possible association was found between the beta3 G-protein C825T marker and LVH. In conclusion, our results suggest an association between LVH and the C825T allele of the G-protein beta3 subunit gene.

Haemodynamic characterization of young normotensive men carrying the 825T-allele of the G-protein beta3 subunit

A C825T polymorphism was recently identified in the gene for the G-protein beta3 subunit, the T-allele being associated with hypertension. To better understand the underlying pathophysiological mechanisms, we compared the haemodynamics of young healthy males with and without the T-allele. In three studies, subjects were investigated with regard to cardiac and vascular function at rest and following intravenous administration of the beta-adrenoceptor antagonist, propranolol, and the alpha2-adrenoceptor agonist, alpha-methylnoradrenaline, and with regard to local venous vasoconstriction in the dorsal hand vein in situ following infusion of the alpha2-adrenoceptor agonist, azepexol. alpha2-Adrenoceptor agonists were chosen as vasoconstrictor drugs since alpha2-adrenoceptors couple to pertussis toxin (PTX)-sensitive G-proteins and since in-vitro studies have demonstrated enhanced signal transduction of PTX-dependent pathways in the presence of the T-allele. Total peripheral resistance was determined as a parameter of vasoconstrictor tone and heart rate, stroke volume and systolic time intervals for cardiac function. T-allele carriers had a significantly elevated stroke volume and lower total peripheral resistance at baseline. After propranolol, their fall in stroke volume was significantly greater. During alpha-methylnoradrenaline infusion, elevation of total peripheral resistance was not increased relative to controls. Similarly, the constriction response of the dorsal hand vein to azepexol was not different. Our study does not support the idea of increased vasoconstrictor tone in T-allele carriers either at rest or during stimulation of alpha2-adrenoceptors. However, this allele may be associated with elevated cardiac stroke volume.

Molecular basis of ethnic differences in drug disposition and response

Ethnicity is an important demographic variable contributing to interindividual variability in drug metabolism and response. In this rapidly expanding research area many genetic factors that account for the effects of ethnicity on pharmacokinetics, pharmacodynamics, and drug safety have been identified. This review focuses on recent developments that have improved understanding of the molecular mechanisms responsible for such interethnic differences. Genetic variations that may provide a molecular basis for ethnic differences in drug metabolizing enzymes (CYP 2C9, 2C19, 2D6, and 3A4), drug transporter (P-glycoprotein), drug receptors (adrenoceptors), and other functionally important proteins (eNOS and G proteins) are discussed. A better understanding of the molecular basis underlying ethnic differences in drug metabolism, transport, and response will contribute to improved individualization of drug therapy.

G protein beta 3 subunit 825T allele, hypertension, obesity, and diabetic nephropathy

The 825T allele of the gene GNB3 which encodes the beta 3 subunit of heterotrimeric G proteins is associated with enhanced signal transduction via G proteins through the generation of a splice variant termed Gbeta3s. It was detected following a classical candidate gene approach using cell lines from patients with enhanced signal transduction and essential hypertension. The high frequency of the 825T allele in 'old' ethnicities, e.g. bushmen and Australian aborigines as well as in black populations, together with its strong association with obesity suggests that the 825T allele is a true 'thrifty genotype'. Development of obesity associated with the 825T allele is strongly influenced by lifestyle, e.g. physical activity, and other exogenous influences like pregnancy. In hypertension the 825T allele is associated with low renin activity and appears to strongly predict the development of left ventricular hypertrophy. In type 2 diabetes the 825T allele was reported to be predispose for end-stage renal disease, whereas this effect has not yet been confirmed for patients with type 1 diabetes.