G protein beta3 subunit variant and essential hypertension in Japanese

The genetic variant C825T of the beta 3 subunit of G protein is associated with hypertension in a Portuguese population

INTRODUCTION

Hypertension is an important public health problem, affecting about 25% of the adult population worldwide.1 Genetic and environmental factors contribute to its pathogenesis. The T allele of the C825T polymorphism of the beta 3 subunit of G protein (rs5443) leads to the production of a truncated variant that enhances intracellular signaling and may interfere with the regulation of blood pressure. This genetic variant has been described as a risk factor for hypertension, although study results are controversial.

OBJECTIVE

The objective of this study was to analyze the association of the C825T polymorphism of the GNB3 gene with the occurrence of hypertension in a Portuguese population from the Madeira archipelago.

METHODS

A case-control study was performed with 1641 Caucasian individuals (mean age 50.6±8.1 years), 848 with hypertension and 793 controls. Blood was collected from all participants for biochemical and genetic analysis, including genotyping of the C825T polymorphism. Logistic regression analysis was performed to determine which variables were significantly associated with the onset of hypertension. Statistical analyses were performed using IBM SPSS version 19.0 and p-values <0.05 were considered statistically significant.

RESULTS

In our study, there was a significant association between the C825T polymorphism of the GNB3 gene and the occurrence of hypertension (odds ratio 1.275; 95% confidence interval 1.042-1.559; p=0.018) in the dominant model, after multivariate analysis.

CONCLUSION

We conclude that the C825T polymorphism of the beta 3 subunit of G protein is significantly and independently associated with the occurrence of hypertension in the study population.

Association between G-protein β3 subunit gene and isolated systolic blood pressure elevation of greater than 130 mmHg: A large-scale cross-sectional study in the Japanese population

AIM

To investigate whether GNB3 C825T single nucleotide polymorphism (SNP) contributes to systolic blood pressure (SBP) ≥ 130 mmHg in a large-scale cross-sectional study among the Japanese population with diastolic blood pressure (DBP) < 85 mmHg.

METHODS

We analyzed 11008 Japanese subjects, including 2797 cases (SBP ≥ 130 and DBP < 85 mmHg) who were not taking anti-hypertensive medication and 8211 controls (SBP < 130 and DBP < 85 mmHg), all of whom enrolled in the genome banking project of the 21^st Century COE (Center of Excellence) Program at Jichi Medical University. Subjects were divided into four groups according to gender (male and female) and age (≤ 49 years and ≥ 50 years). GNB3 gene polymorphism was determined using the TaqMan probe method. We compared the frequencies of alleles and genotypes between cases and controls by chi-squared test. The strength of the associations was estimated by odds ratios (ORs) and 95%CI by using logistic regression analysis. The ORs were adjusted for age and body mass index.

RESULTS

Allele and genotype distributions significantly differed between cases and controls only in males aged ≤ 49 years. Compared to the CC genotype, a significant OR was obtained in the TT genotype among males aged ≤ 49 years.

CONCLUSION

This study indicates that the TT genotype of the GNB3 C825T SNP may contribute to SBP elevation of greater than 130 mmHg compared to the CC genotype in Japanese males aged ≤ 49 years.

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.

Hypertension-associated C825T polymorphism impairs the function of Gβ3 to target GRK2 ubiquitination

Population-based and case-control studies in different ethnicities have linked a polymorphism, C825T, in exon 10 of GNB3 gene to hypertension and several additional diseases. The 825T allele is associated with alternative splicing and results in a shortened Gβ3 protein, referred to as Gβ3s, which loses 41 amino acids encompassing one WD40 repeat domain. The mechanism of how Gβ3 C825T polymorphism is associated with hypertension has remained unclear, but an impairment of its canonical function in G-protein-coupled receptor signaling has been ruled out. Here, we report that Gβ3, like other Gβ proteins, binds to DDB1 and assembles a DDB1-CUL4A-ROC1 E3 ubiquitin ligase (CRL4A(Gβ3)) to target GRK2 ubiquitination. The loss of the 41 amino-acid residues disrupts the Gβ3-DDB1 binding and impairs the function of Gβ3s to ubiquitinate GRK2. GRK2 ubiquitination levels were decreased and protein levels were accumulated in the blood samples of Gβ3 825T allele carriers. Deletion of Cul4a in mice resulted in systolic pressure increased and weakened heart function in male mice that can be partially rescued by the deletion of one Grk2 allele. These results reveal a mechanism explaining the link between Gβ3 C825T polymorphism and hypertension.

Molecular genetics of essential hypertension

Hypertension is a major public health problem in the developing as well as in developed countries due to its high prevalence and its association with coronary heart disease, renal disease, stroke, peripheral vascular disease, and related disorders. Essential hypertension (EH) is the most common diagnosis in this disease, suggesting that a monocausal etiology has not been identified. However, a number of risk factors associated with EH have also been identified such as age, sex, demographic, environmental, genetic, and vascular factors. Recent advances in molecular biological research had achieved clarifying the molecular basis of Mendelian hypertensive disorders. Molecular genetic studies have now identified mutations in several genes that cause Mendelian forms of hypertension in humans. However, none of the single genetic variants has emerged from linkage or association analyses as consistently related to the blood pressure level in every sample and in all populations. Besides, a number of polymorphisms in candidate genes have been associated with differences in blood pressure. The most prominent candidate has been the polymorphisms in the renin-angiotensin-aldosterone system. In total, EH is likely to be a polygenic disorder that results from inheritance of a number of susceptibility genes and involves multiple environmental determinants. These determinants complicate the study of blood pressure variations in the general population. The complex nature of the hypertension phenotype makes large-scale studies indispensable, when screening of familial and genetic factors was intended. In this review, recent genetic studies exploring the molecular basis of EH, including different molecular pathways, are highlighted.

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 polymorphisms and essential hypertension: a case-control association study in northern Han Chinese

OBJECTIVE

To explore the association between the three polymorphisms [ C825T, C1429T and G(-350)A] of the gene encoding the G protein beta 3 subunit (GNB3) and hypertension by performing a case-control study in the northern Han Chinese population.

METHODS

We recruited 731 hypertensive patients and 673 control subjects (the calculated power value was > 0.8). Genotyping was performed to identify C825T, C1429T and G(-350)A polymorphisms using the TaqMan assay. Comparisons of allelic and genotypic frequencies between cases and controls were made by using the chi-square test. Logistic regression analyses were performed to investigate the relationships between the three polymorphisms of GNB3 gene under different genetic models (additive, dominant and recessive models).

RESULTS

The genotype distribution and allele frequencies of C825T, C1429T and G(-350)A polymorphisms did not differ significantly between hypertensive patients and control subjects, either when the full sample was assessed, or when the sample was stratified by gender. No significant association was observed between C825T, C1429T and G(-350)A polymorphisms and the risk of essential hypertension in any genetic model. Linkage disequilibrium was only detected between C825T and C1429T polymorphisms. Haplotype analyses observed that none of the three estimated haplotypes significantly increased the risk of hypertension.

CONCLUSIONS

Our study suggested that the GNB3 gene polymorphisms [C825T, C1429T and G(-350)A] were not significantly associated with essential hypertension in northern Han Chinese population.

The C825T polymorphism of the G-protein β3 subunit gene and its association with hypertension and stroke: an updated meta-analysis

OBJECTIVE

Several epidemiological studies have evaluated the association between the GNB3 C825T polymorphism and hypertension or stroke. The results of these studies were inconsistent; therefore, we performed a meta-analysis to clarify these discrepancies.

METHODS

We systematically searched the PubMed, Embase, Web of Science, CNKI, and CBM databases, and manually searched reference lists of relevant papers, meeting abstracts, and relevant journals. Pooled odds ratios (ORs) and 95% confidence intervals (CIs) were calculated for dominant, recessive, and allelic models. A fixed or random effects model was separately adopted depending on study heterogeneity. Subgroup and sensitivity analyses were performed to detect study heterogeneity and examine result stability, respectively. Publication bias was tested using funnel plots, the Egger's regression test, and Begg's test.

RESULTS

We screened 66 studies regarding hypertension and eight concerning stroke. A combined analysis showed that only the allelic model found a marginal association with hypertension (OR = 1.07, 95% CI = 1.01-1.13) and female gender (OR = 1.11, 95% CI = 0.99-1.24). However, no comparison models found an association with stroke (allelic model: OR = 1.11, 95% CI = 0.94-1.32; dominant model: OR = 1.16, 95% CI = 0.92-1.48; and recessive model: OR = 1.05, 95% CI = 0.97-1.14). Sensitivity analysis suggested that all models did not yield a relationship to hypertension or stroke among Asians. Besides, there was a lack of statistical association with hypertension in Caucasians, which maybe due to a small sample size. When we restricted the included studies to normal populations according to the Hardy-Weinberg equilibrium, no association was found.

CONCLUSIONS

There was no evidence indicating that the 825T allele or TT genotype was associated with hypertension or stroke in Asians or hypertension in Caucasians. However, further studies regarding Africans and other ethnicities are needed to identify further correlations.

The role of G protein β3 subunit polymorphisms C825T, C1429T, and G5177A in Turkish subjects with essential hypertension

Hypertension is a multifactorial disorder that constitutes a major risk factor for the cardiovascular system. Heterotrimeric G-proteins, which couple receptors for diverse extracellular enzymes or ion channels, are correlated with disease mechanisms. Several studies have demonstrated an association between G protein polymorphisms and essential hypertension in some populations, although contradictive results also exist. In this study, we have investigated the potential role of the C825T, C1429T, and G5177A polymorphisms of the β3 subunit of G-proteins in essential hypertension in a group of Turkish subjects. Genomic DNA from 106 normotensive individuals (117.4 ± 13.1, 75.2 ± 10.5; systolic blood pressure (SBP) and diastolic blood pressure (DBP) levels, respectively) and 101 hypertensive subjects (152.3 ± 18.0, 92.5 ± 11.6; SBP and DBP levels, respectively) were studied by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and direct sequencing methods for these polymorphisms. Allele frequencies of the polymorphisms were consistent with Hardy Weinberg equilibrium, except for the C825T polymorphism (χ(2) = 7.8). The frequencies of the 825T and 1429T variants were higher in hypertensive subjects compared to those of controls. Differences between hypertensives and controls were not statistically significant, though difference was very close to significance for C825T (p = 0.056 and 0.099 for 825T and 1429T, respectively). T allele frequency in overall population showed significant association with hypertension for C825T (0.0134). The prevalence of the 5177A-variant was very low and all subjects carrying it were heterozygotes in both groups.

The --1019 C/G polymorphism of the 5-HT(1)A receptor gene is associated with negative symptom response to risperidone treatment in schizophrenia patients

The application of pharmacogenetics is currently one of the most promising developments in anti-psychotic treatment and is attracting more and more attention. Although risperidone belongs to the first-line atypical anti-psychotics, there have been relatively few risperidone pharmacogenetic studies, especially in Asian populations. We investigated the relationship between the C825T polymorphism of GBN3 (rs5443) and the -1019 C/G polymorphism of 5-HT(1)A (rs6295) and response to risperidone treatment. One-hundred and thirty schizophrenia patients were recruited. They were treated with risperidone monotherapy for eight weeks. Clinical response was assessed on the Positive and Negative Syndrome Scale (PANSS) on the day of admission and was subsequently assessed after eight weeks following the treatment. Patients were genotyped for two functional polymorphisms: C825T of GBN3 (rs5443) and -1019 C/G of HT(1)A (rs6295). Association tests between genotypes and percentage improvement in total PANSS scores, as well as positive symptom scores and negative symptom scores, were performed using analyses of variance (ANOVA). The -1019 C/G polymorphism of HT(1)A (rs6295) was associated with negative symptom response to treatment. Patients with the CC genotype showed substantial improvement as regards negative symptom response (F = 4.177, df = 2, P = 0.019), compared with the patients with the CG and GG genotypes. No association was observed between C825T of GBN3 (rs5443) and changes in PANSS scores. The results suggest that the -1019 C/G polymorphism (rs6295) in the 5-HT(1)A gene may be a useful predictor of reduction in negative symptoms in schizophrenic patients treated with risperidone.

Association of insulin sensitivity and glucose tolerance with the c.825C>T variant of the G protein beta-3 subunit gene

The risk of macrovascular complications of diabetes mellitus is greatly enhanced by the presence of high blood pressure. In addition, hypertension and diabetes share insulin resistance as a common pathophysiological mechanism. Despite evidence for a common molecular genetic background of insulin resistance, glucose intolerance, and hypertension, few candidate genes have been shown to influence all of these features simultaneously. We examined the association of insulin sensitivity with the c.825C>T variant of the g-protein beta-3 subunit (GNB3), a candidate gene of hypertension, in families of Mexican-American hypertensive patients.

METHODS

One hundred eighty subjects enrolled in a family study of Mexican-American hypertensive patients were recruited from hypertension clinics in Los Angeles. Subjects underwent pretreatment blood pressure recording, an oral glucose tolerance test, euglycemic hyperinsulinemic clamp, and anthropometric measurements. DNA from peripheral blood leukocytes was genotyped by polymerase chain reaction and restriction enzyme digest with BseD1 (GNB). Statistical analysis was performed by transmission disequilibrium testing.

RESULTS

In carriers of the T-allele, blood glucose was significantly lower [(mean+S.D.) fasting: 96.7+22.9 vs. 106.7+51.7mg/dl, P=.009; oral glucose tolerance test (oGTT) 120 min: 131.7+48.7 vs. 137.8+64.9 mg/dl, P=.036], and insulin sensitivity was significantly higher (229.0+108.7 vs. 188.5+94.2 mg/kg per minute, P=.037) than in homozygous carriers of the C-allele. Blood pressure did not differ significantly between the phenotypes.

CONCLUSION

In a Mexican-American hypertensive population, we found evidence for higher insulin sensitivity in carriers of the T allele of the c.825C>T variant of GNB3.

Homozygous 825T allele of the GNB3 protein influences the susceptibility of Japanese to dyspepsia

The role of genetics in the susceptibility to functional dyspepsia (FD) is not well established. Recently, two different associations were reported between FD and G-protein beta3 (GNB3) subunit gene polymorphism. We aim to clarify the association between GNB3 protein C825T polymorphism and dyspepsia in the Japanese population. Eight-nine dyspeptics and 94 nondyspeptic subjects enrolled in this study. All subjects underwent gastroscopy and patients with significant upper gastrointestinal findings were excluded. Other diseases were also excluded by face-to-face history and physical examination. GNB3 protein C825T polymorphisms were determined by polymerase chain reaction-restriction fragment-length polymorphism. H. pylori infection status was examined by histology or antibody against H. pylori. Nonsignificant correlation was found between GNB3 protein homozygous 825T and unexplained dyspepsia (OR = 1.65, 95% CI: 0.87-3.13). However, among H. pylori-negative subjects, homozygous GNB3 protein 825T significantly increased the risk of dyspepsia (16.7% versus 40.5%; CC versus TT; OR = 5.10, 95% CI: 1.21-21.43, CC versus others; OR = 3.40, 95% CI: 1.16-9.93, respectively). This significant association remained after logistic regression analysis with adjustment for sex and age (CC versus TT; OR = 5.73, 95% CI: 1.27-25.82, CC versus others; OR = 3.08, 95% CI: 1.02-9.25). No significant correlation was found between GNB3 polymorphism and any dyspeptic symptoms. Our data suggest that the homozygous 825T allele of GNB3 protein is associated with dyspepsia in the H. pylori-negative Japanese population. The role of genetics in the development of dyspepsia needs further evaluation.

Association study on GNB3 gene polymorphism with essential hypertension in Xinjiang Uygur group

The relationship between the tenth exon C825T of G-protein β3 subunit (GNB3) genetic polymorphism and hypertension in the Uygur population of China was investigated. A nested case-control study (n = 738) was carried out. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique was used to genotype GNB3 C825T polymorphism in 354 hypertensive (HT) and 384 normotensive (NT) Uygur subjects. The distributions of GNB3 C825T genotypes were CC (27.2%), TT (42.9%), and CT (29.9%) in the hypertensive subjects and CC (27.7%), TT (42.4%), CT (29.9%) in the normotensive subjects. There were no significant differences in the genotype distributions between the two groups (χ (2) = 0.0262 P = 0.99). The T allele was 51.4% in hypertensive subjects and 51.2% in normotensive subjects, which, between the two groups, was not a significant difference (χ (2) = 0.0016 P = 0.97). Further analysis shows that there is no association between C825T genotypes and age, body mass index (BMI), Glucose (GLU), Triglyceride (TG), Cholesterol (CHO), systolic blood pressure (SBP) and diastolic blood pressure (DBP). No evidence was found to suggest an association between GNB3 C825T polymorphism and hypertension in the Uygur population of China.

The GNB3 C825T polymorphism and essential hypertension: a meta-analysis of 34 studies including 14,094 cases and 17,760 controls

OBJECTIVES

The C825T single nucleotide polymorphism of the G-protein beta3 (GNB3) has been implicated in susceptibility to essential hypertension, through the expression of an alternatively spliced truncated variant. In an effort to clarify earlier inconclusive results, we performed a meta-analysis of population-based case-control genetic association studies.

METHODS

Random-effects methods were applied on summary data in order to combine the results of the individual studies.

RESULTS

We identified in total 34 studies, including 14,094 hypertensive cases and 17,760 controls. The TT versus CC + CT contrast yielded an overall odds ratio (OR) of 1.08 [95% confidence interval (CI): 1.01, 1.15], the contrast of TT + CT versus CC, an OR of 1.17 (95% CI: 1.06, 1.29), whereas that of the T allele versus C allele yielded a non-significant OR of 1.05 (95% CI: 0.98, 1.13). There was moderate evidence for a publication bias in the latter two contrasts, which was eliminated after excluding studies not in Hardy-Weinberg equilibrium and those performed on non-normal populations (those with a diagnosis of diabetes, obesity and myocardial infarction). Subgroup analyses revealed that non-significant estimates arose from studies on Asian populations, as opposed to the Caucasian ones. Furthermore, the frequency of the T allele was lower in Caucasians and these populations were found to inhabit higher latitudes.

CONCLUSIONS

The findings are in agreement with a recently proposed causal model for systolic blood pressure, which correlates it with the T allele and the absolute latitude. Further studies are needed in order to fully address questions about the aetiological mechanism of the particular association, as well as to study the effect in populations of African descent.

Gene-environment interaction and the GNB3 gene in the Atherosclerosis Risk in Communities study

OBJECTIVE

The purpose of this study was to investigate the interaction between the G-protein beta-3 (GNB3) 825C>T polymorphism and physical activity in relation to prevalent obesity and hypertension.

RESEARCH METHODS AND PROCEDURES

The GNB3 825C>T genotype was measured in a sample of 14,716 African Americans (AAs) and whites from the Atherosclerosis Risk in Communities (ARIC) study, and logistic regression was used to test for genetic effects and gene-environment interactions.

RESULTS

The GNB3 825C>T variant was not independently associated with prevalent obesity or hypertension in either AA or whites. However, we observed a significant interaction (P<0.001) between this variant and physical activity in predicting obesity status in AAs. In AAs who were active, each 825T allele was associated with a 20% lower prevalence of obesity (odds ratio (OR)=0.80, 95% confidence interval (CI)=0.689-0.937, P=0.005), whereas each 825T allele was associated with a 23% greater prevalence of obesity for low-active individuals (OR=1.23, 95% CI=1.06-1.44, P=0.008). We also found a significant interaction between the GNB3 825C>T polymorphism, obesity status and physical activity in predicting hypertension in the AA subjects. AA homozygotes for the 825T allele who were both obese and had a low activity level were 2.7 times more likely to be hypertensive, compared to non-obese, active 825C homozygotes (OR=2.71, 95% CI=1.19-6.17, P<0.02).

DISCUSSION

Our findings suggest that the variation within the GNB3 gene may interact with physical activity level to influence obesity status and, together with obesity and physical activity, the GNB3 825C>T variant may influence hypertension prevalence in AAs.

Association of the C825T polymorphism of the G-protein beta3 subunit gene with hypertension, obesity, hyperlipidemia, insulin resistance, diabetes, diabetic complications, and diabetic therapies among Japanese

A C825T polymorphism of the gene encoding the G-protein beta3 subunit (GNB3) is associated with increased intracellular signal transduction. We know that this C825T polymorphism may influence hypertension and obesity. In whites, the C825T polymorphism has been reported to induce hypertension, obesity, and diabetic nephropathy. Thus, we investigated how genetic variation in the GNB3 gene is associated with hypertension, obesity, insulin resistance, diabetes, diabetic complications, and diabetic therapies in 427 Japanese subjects with type 2 diabetes mellitus and in 368 Japanese subjects who underwent general health examinations. The frequency of the GNB3 gene polymorphism was 0.48 and 0.47 in subjects with diabetes and in those who had general health examinations, respectively. The amount of hyperlipidemia of the CT allele was significantly lower than the amount in the CC allele in the Japanese subjects with diabetes. Our results suggest that the C825T polymorphism influences lipid metabolism and is not associated with hypertension, obesity, insulin resistance, diabetes, diabetic complications, or diabetic therapies.

G-protein beta3 subunit variant C825T is a risk factor for hypertension in Japanese females--a prospective cohort study over 5 years

The relationship between the G-protein beta3 subunit variant C825T and risk of hypertension was examined in a prospective cohort study of Japanese workers. This study included observations over a 5-year period from 1997 to 2002 on 878 males and 692 females who were normotensive at entry. Hypertension was defined as systolic blood pressure > or =140 mmHg and/or diastolic blood pressure > or =90 mmHg, or taking antihypertensive medication. Pooled logistic regression analyses were performed using C825T genotype, age, body mass index, lifestyle, and the result of blood chemistries as the covariates. Multivariate pooled logistic regression analysis showed the risk of hypertension was 2.31 times higher in females with the TT genotype than in females with the CC genotype (95% confidence interval: 1.07-4.96), after adjustment for the effects of other potential covariates. In contrast, no significant risk of hypertension was observed with the TT genotype in male subjects. This study indicates that the 825T allele is an independent risk factor for hypertension in Japanese females, and suggests that this polymorphism may be a beneficial prognostic marker for hypertension in the general Japanese female population.

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.

Polymorphisms in four candidate genes in young patients with essential hypertension

AIM

To determine whether four potential genetic factors (polymorphisms in genes for alpha-adducin, beta-adducin, the G-protein beta-3 subunit and nitric oxide synthase) are important for the development of essential hypertension (EH) in Slovenian children and young adults with EH.

METHODS

Both a nuclear families approach and case-control study have been performed. Genotyping of common polymorphisms in these genes using polymerase chain reaction was carried out in 104 nuclear families (an affected child, both parents) and in 200 control patients.

RESULTS

Using the transmission disequilibrium test, no statistically significant differences were found between the frequencies of transmitted and non-transmitted alleles in nuclear families for all four investigated polymorphisms. In addition, the distributions of genotypes and alleles for the four polymorphisms did not differ significantly between our children and 200 healthy control patients. The allele frequencies of all polymorphisms were concordant with those observed in some other Caucasian populations.

CONCLUSION

We found no association between the investigated gene variants and EH, so we conclude that they do not confer a significantly increased risk of the development of EH in the Slovenian population of hypertensive children.

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.

G Protein β3 Subunit Gene Variants and Essential Hypertension in the Northern Chinese Han Population

Recently a novel C825T polymorphism in the G protein beta3 subunit gene was identified that showed an association with hypertension in a German population; the results of studies in other populations have been inconsistent. To examine the contribution of GNB3 polymorphisms to the development of hypertension in the northern Chinese Han population, we conducted a case-control study consisting of 501 hypertensive cases and 503 controls using the G(-350)A, C825T and C1429T polymorphisms. Genotypes of samples were determined by PCR and restriction digestion. Single locus analysis showed a significant association between G(-350)A and hypertension (P = 0.01) but no association for C825T or C1429T. The three polymorphisms were in tight linkage disequilibrium (D'=-1 for G(-350)A-C825T, D'= 0.92 for C825T-C1429T) and a total of 7 haplotypes were observed in the entire population. Haplotype A-C-C was found to be significantly related to hypertension (P = 0.032) and A-C-C carriers had a more than two-fold higher risk of hypertension than non-carriers, after adjustment for BMI and glucose. In conclusion, our study suggests that G(-350)A is a potential functional polymorphism that may be related to hypertension, whereas the C825T and C1429T polymorphisms are not associated with hypertension in the northern Chinese Han population.

G Protein Polymorphisms in Hypertension, Atherosclerosis, and Diabetes

A common C825T polymorphism in the gene GNB3, which encodes the beta 3 subunit of heterotrimeric G proteins, was identified in cell lines from patients with hypertension. The 825T allele is associated with increased intracellular signal transduction. Many population-based and case-control studies in different ethnicities have investigated an association between this polymorphism and hypertension, obesity, and atherosclerosis. A critical assessment of published studies suggests that 825T allele carriers have an increased risk for hypertension combined with features of the metabolic syndrome, such as dyslipidemia, hypercholesterolemia, insulin resistance, and obesity. It is anticipated that this polymorphism will be used in clinical practice to better characterize hypertension and for individualized treatment regimens.

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.

Association of GNB3 gene with pulse pressure and clustering of risk factors for cardiovascular disease in Japanese

Heterotrimeric guanine nucleotide-binding proteins (G proteins) mediate many pathways including the beta-adrenergic signaling pathway. The C825T polymorphism in the gene coding for the beta3 subunit of G proteins (GNB3) has been shown to be associated with several phenotypes such as hypertension, obesity, and diabetes mellitus comprising the metabolic syndrome. The GNB3 C825T polymorphism may therefore be associated with many atherosclerosis-related phenotypes. On these grounds, we studied the C825T polymorphism in relation to atherosclerosis-related phenotypes in a large Japanese population. Analyses in general linear models showed that T carriers had a significantly wider pulse pressure (P=0.0089) as well as a significantly higher systolic blood pressure (P=0.026). In contrast, analyses in logistic regression models showed that the C825T polymorphism was not significantly associated with each of the four major classical risk factors for cardiovascular and cerebrovascular disease (obesity, hypertension, hypertriglyceridemia, and diabetes mellitus). However, a significantly higher percentage of subjects had none of the four disorders in CC homozygotes than in T carriers (P=0.026). Thus, the C825T polymorphism was significantly associated with clustering of these four risk factors. Although the effect of the gene on each phenotype appears to be weak, considering the combined impact of the effects of the C825T polymorphism on risk factors, the GNB3 gene may be an important gene for human health.

Lack of association of human G-protein ??3 subunit variant with hypertension in Japanese workers

OBJECTIVE

To examine the association between hypertension and the C825T polymorphism in the G-protein beta 3 subunit gene in Japanese workers.

METHODS

This study used logistic regression analysis and multiple regression analyses to investigate whether the C825T polymorphism was associated independently with hypertension or blood pressure when factors such as age, body mass index, blood chemistry and lifestyle were taken into consideration. The target subjects were 1452 male and 1169 female workers selected from 3834 male and 2591 female workers in a single company. Hypertension was defined as a systolic blood pressure > or = 140 mmHg and/or diastolic blood pressure > or = 90 mmHg, or taking antihypertensive medication. The power of the study was estimated as 83% for males and 41% for females based on allelic frequencies in Caucasians.

RESULTS

Genotype distributions for C825T in hypertensive males (CC = 58, CT = 135, TT = 63) and females (CC = 20, CT = 36, TT = 20) were not significantly different from normotensive males (CC = 300, CT = 614, TT = 282) or females (CC = 274, CT = 602, TT = 217), respectively. Allele distributions were not significantly different in either sex. Multiple logistic regression analysis showed that genotype was not associated significantly with hypertension, whereas there was a significant relationship between hypertension and age, family history of hypertension, body mass index, hematocrit, platelet count, gamma-glutamyl transpeptidase (gamma-GTP) and uric acid. Data analysis using one-way analysis of variance and multiple regression showed that the C825T allele had no significant influence on either systolic, diastolic or mean blood pressure.

CONCLUSIONS

This study indicates that the C825T polymorphism is not a significant factor for hypertension or blood pressures in Japanese people. Targeting of this polymorphism is therefore unlikely to be beneficial when attempting to prevent hypertension in the general Japanese population.

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.

Essential hypertension: genes and dreams

Herein we review all of the data from linkage by genome scanning and from association studies in essential hypertension. Genome scans have yielded loci linked to hypertension on almost every chromosome. We tabulate all of these loci to highlight the striking inconsistency. Similarly, association studies have implicated > 66 genes to date, which we also list, but virtually all have failed to show consistent replication in other settings. Nevertheless, we believe that molecular genetics should eventually find all of the major gene variants for essential hypertension. This will be a great scientific achievement and lead to new treatments. The dream, however, of using this information in clinical genetic testing could turn out to be a nightmare. Thus at present the hype surrounding genes for complex polygenic diseases like hypertension far exceeds the reality.

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.

Matrix analysis for the dissection of interactions of G-protein beta3 subunit C825T genotype, allograft function, and posttransplant hypertension in kidney transplantation

BACKGROUND

Complex relationships between genes and environment and the resulting biological impact have been dissected predominantly by conventional association studies. A major limitation of such studies results from the fact that only bidirectional investigations of genes and clinical end-points are commonly performed. The authors, therefore, applied matrix analyses to account for interactions between genetic and environmental factors influencing kidney allograft function.

METHODS

By using matrices of correlation coefficients we tested the genetic effect of a variant within the gene encoding the beta3-subunit of heterotrimeric G-proteins (Gbeta3-C825T polymorphism) on posttransplant hypertension and kidney allograft function. This strategy allowed the authors to account for the influence of additional well-established genetic, clinical, and environmental confounders. The authors studied 281 consecutive white kidney recipients recruited between 1988 and 1993. Correlation coefficients of indices of relative change (percent) of systolic blood pressure (BP) and creatinine clearance (CrCl) were used in correlation coefficient matrices to elucidate interactions of parametrical biological parameters with environmental and genetic risk factors.

RESULTS

A significant relationship was found between decreasing CrCl and increasing systolic BP in only those recipients who carried the Gbeta3-825TT genotype and did not lose graft during the first 3 years (R2 = 0.25; P = 0.021).

CONCLUSIONS

In transplant recipients who did not lose their graft during the first 3 years after transplantation, the Gbeta3-TT genotype contributed to accelerated loss of allograft function by exaggeration of posttransplant hypertension. This relationship could only be elucidated by means of matrix analyses that allow the detection of complex relations between clinical, genetic, and environmental factors.

Positive association of maternal G protein beta3 subunit 825T allele with reduced head circumference at birth

G protein beta3 subunit C825T polymorphism, which has previously been studied in association with common disorders in adults such as hypertension and obesity, has been focused upon recently for a possible important role in fetal metabolism. Japanese are characterized by having equal allele frequencies for this polymorphism. In this study, we determined the maternal and infantile genotypes in 342 pairs of normal healthy mothers and their infants, and compared the genotype frequencies with various infantile somatoscopic characteristics converted into SD units according to sex, parity and gestational weeks. We observed an association of the maternal (but not infantile) G protein beta3 subunit 825T allele with reduced head circumference but not with reduced birth weight of the neonate. No association was observed between G protein beta3 subunit C825T polymorphism and various maternal somatoscopic characteristics. Although detailed mechanism of this association requires further research, our results suggest that expression of the beta3 subunit 825T allele in the mother may exert influence on fetal metabolic environment, perhaps through changes in the maternal uterine environment, or on maternal metabolism.

G protein beta3 subunit variant: tendency of increasing susceptibility to hypertension in Japanese

The mechanism of human G beta mutation, G beta3-s, to produce a "gain-of-function" G-protein signaling abnormality remains to be elucidated. Both the enhanced Gi-mediated signalings and the expression of G beta3-s have been demonstrated to be associated with hypertension, together with the finding that the T825 variant might be associated with the occurrence of a splice variant GNB3-s in a white population. The aim of the present study was to reveal a key role of G beta by confirming the association between this polymorphism and susceptibility of hypertension in Japanese. Genotype analysis of 180 normotensive and 179 hypertensive subjects suggests that the T allele tends to be related to the prevalence of hypertension. When age, sex and body mass index were controlled by multiple logistic regression, odds ratios for hypertension associated with the T allele were 1.77 (TT vs CC; 95% confidence interval (CI) 0.97-3.21; p = 0.06), 1.13 (TC vs CC; 95% CI 0.62-2.05; p = 0.69) and 1.40 (TT + TC vs CC; 95% CI 0.81-2.40; p = 0.23). The T allele frequency was found to be significantly higher in hypertensives than in normotensives (0.63 vs 0.56; chi2 = 4.27; p = 0.04), both of which are considerably higher than the frequency observed in Whites. Higher T allele frequencies in Japanese may represent one of the ethnic differences: a larger subgroup whose hypertension is increased by excessive salt diet. Confirming the association between the T allele and hypertension by further investigation and then utilizing the various intermediate features or phenotypes, such as Na+/H+ exchanger activity and renin levels, may help to unravel the active role of the beta subunit.

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.

Genetic analysis in human hypertension

Hypertension is considered to be a complex trait to which genetic, environmental, and demographic factors contribute interactively. Recently, molecular genetic studies have achieved remarkable success in the elucidation of causative mutations in several Mendelian hypertensive disorders in which single nucleotide polymorphisms (SNPs) disrupt the function of single genes, thereby leading to unambiguous phenotypes. It seems unlikely, however, that such a simple base-substitution is the primary mechanism in cases of essential hypertension, even if SNPs modify the relevant gene function to some extent. Despite the enormous efforts made to date, no consistent association between any of the candidate genes and essential hypertension has been established. One plausible explanation is that because individual genes play a modest role in the pathogenesis of hypertension, confounding variables, whether individual (sex, ethnic origin, etc.) or environmental, may decrease the chance of identifying a causative relation between the genes and hypertension, depending on the populations studied. Several approaches can be proposed to overcome this problem, including long-term follow-up of clinical events collected to attain sufficient phenotypic information and statistical power. With the recent advances in high-throughput genotyping techniques and bioinformatic strategies, it has become possible to perform even SNP-based genome-wide screening. At present, however, the need for identification of susceptibility genes for hypertension still poses a great and unanswered challenge. Nonetheless, we believe that a precise understanding of the manner in which genetic variations affect hypertension can be achieved, and that clarification of the associated phenotypes will lead to the development of effective preventive and treatment strategies.

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.

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.