G protein beta3 subunit 825T allele and its potential association with obesity in hypertensive individuals

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.

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.

The Human Obesity Gene Map: The 2003 Update

This is the tenth update of the human obesity gene map, incorporating published results up to the end of October 2003 and continuing the previous format. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, quantitative trait loci (QTLs) from human genome-wide scans and animal crossbreeding experiments, and association and linkage studies with candidate genes and other markers is reviewed. Transgenic and knockout murine models relevant to obesity are also incorporated (N = 55). As of October 2003, 41 Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and causal genes or strong candidates have been identified for most of these syndromes. QTLs reported from animal models currently number 183. There are 208 human QTLs for obesity phenotypes from genome-wide scans and candidate regions in targeted studies. A total of 35 genomic regions harbor QTLs replicated among two to five studies. Attempts to relate DNA sequence variation in specific genes to obesity phenotypes continue to grow, with 272 studies reporting positive associations with 90 candidate genes. Fifteen such candidate genes are supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. Overall, more than 430 genes, markers, and chromosomal regions have been associated or linked with human obesity phenotypes. The electronic version of the map with links to useful sites can be found at http://obesitygene.pbrc.edu.

The Human Obesity Gene Map: The 2004 Update

This paper presents the eleventh update of the human obesity gene map, which incorporates published results up to the end of October 2004. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, transgenic and knockout murine models relevant to obesity, quantitative trait loci (QTLs) from animal cross-breeding experiments, association studies with candidate genes, and linkages from genome scans is reviewed. As of October 2004, 173 human obesity cases due to single-gene mutations in 10 different genes have been reported, and 49 loci related to Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and causal genes or strong candidates have been identified for most of these syndromes. There are 166 genes which, when mutated or expressed as transgenes in the mouse, result in phenotypes that affect body weight and adiposity. The number of QTLs reported from animal models currently reaches 221. The number of human obesity QTLs derived from genome scans continues to grow, and we have now 204 QTLs for obesity-related phenotypes from 50 genome-wide scans. A total of 38 genomic regions harbor QTLs replicated among two to four studies. The number of studies reporting associations between DNA sequence variation in specific genes and obesity phenotypes has also increased considerably with 358 findings of positive associations with 113 candidate genes. Among them, 18 genes are supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. Overall, >600 genes, markers, and chromosomal regions have been associated or linked with human obesity phenotypes. The electronic version of the map with links to useful publications and genomic and other relevant sites can be found at http://obesitygene.pbrc.edu.

C825T Polymorphism of the G Protein β3Subunit Is Associated with Obesity but Not with Insulin Sensitivity

OBJECTIVE

The common C825T polymorphism of the gene that encodes the G protein beta3 subunit has been shown to influence lipolysis in human adipocytes and to be associated with hypertension, body fat distribution, and obesity. In addition, it has been shown to be associated with insulin resistance in a small group of hypertensive subjects. We investigated whether this polymorphism contributed to the variability in obesity in our population from southern Germany and whether it was associated with insulin sensitivity of lipolysis and/or glucose disposal.

RESEARCH METHODS AND PROCEDURES

We determined percentage body fat, body fat distribution, glucose tolerance [oral glucose-tolerance test (OGTT)], insulin sensitivity, and serum free fatty acids using data from OGTTs (N = 774) and clamp (euglycemic hyperinsulinemic clamp, N = 216) in normal and impaired glucose tolerant subjects who were genotyped for this polymorphism.

RESULTS

Compared with noncarriers of the C825T mutation, subjects with the C825T variant (prevalence approximately 32%) had higher percentage body fat (p = 0.02) and higher BMI (p = 0.03). No conclusive effect was seen on serum free fatty acids measured either during fasting or at the end of a 2-hour OGTT. Insulin sensitivity determined during the OGTT and during the clamp, both adjusted for age, gender, and percentage body fat, was not different between the genotypes (p = 0.33 and p = 0.48, respectively).

DISCUSSION

We have concluded that the C825T polymorphism in the G protein beta3 subunit played an important role in the determination of obesity in this German population. However, it probably had no direct effects on insulin sensitivity of lipolysis and glucose disposal.

Association of the C825T polymorphism in the GNB3 gene with obesity and metabolic phenotypes in a Taiwanese population

The relationship between obesity and a single nucleotide polymorphism (SNP), rs5443 (C825T), in the guanine nucleotide binding protein beta polypeptide 3 (GNB3) gene is currently inconsistent. In this study, we aimed to reassess whether the GNB3 rs5443 SNP could influence obesity and obesity-related metabolic traits in a Taiwanese population. A total of 983 Taiwanese subjects with general health examinations were genotyped. Based on the criteria defined by the Department of Health in Taiwan, the terms "overweight" and "obesity" are defined as 24 ≦ BMI < 27 and BMI ≧ 27, respectively. Compared to the carrier of the combined CT + TT genotypes of the GNB3 rs5443 polymorphism, triglyceride was significantly higher for the carrier of CC genotype in the complete sample population (128.2 ± 93.2 vs. 114.3 ± 79.1 mg/dl; P = 0.041). In addition, the carriers of CC variant had a higher total cholesterol than those with the combined CT + TT variants (194.5 ± 36.8 vs. 187.9 ± 33.0 mg/dl; P = 0.019) in the complete sample population. In the normal controls, both triglyceride (P = 0.018) and total cholesterol (P = 0.011) were also significantly higher in the CC homozygotes than in the combined CT + TT genotypes. However, the GNB3 rs5443 SNP did not exhibit any significant association with obesity or overweight among the subjects. Our study indicates that the CC genotype of the GNB3 rs5443 SNP may predict higher obesity-related metabolic traits such as triglyceride and total cholesterol in non-obese Taiwanese subjects (but not in obese subjects).

The GNB3 C825T polymorphism as a pharmacogenetic marker in the treatment of hypertension, obesity, and depression

Heterotrimeric guanine-binding proteins (G proteins) transmit signals from the cell surface to intracellular signal cascades. The β3-subunit encoded by the gene GNB3 is widely expressed and, therefore, involved in various physiological and pathophysiological processes. A C825T polymorphism located in exon 10 of GNB3 was described in 1998 and the T allele was associated with alternative splicing and with increased signal transduction in human cells and tissues. In several disease-association studies, the 825T allele could be linked to hypertension, obesity, and depression. Meta-analysis available for hypertension and depression confirmed association with these phenotypes. On the basis of these findings, subsequent studies investigated whether the C825T polymorphism serves as a pharmacogenetic marker. Most pharmacogenetic investigations have focused on the treatment of hypertension, obesity, and depression. In this study, we will comprehensively describe and discuss these studies.

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.

Interactions of genetic variants with physical activity are associated with blood pressure in Chinese: the GenSalt study

BACKGROUND

Blood pressure (BP) homeostasis involves complex interactions among genetic and nongenetic factors, providing major challenges to dissection of the genetic components that influence BP and hypertension. In this study, we examine the effects of interaction of genetic variants with physical activity on BP in a relatively genetically homogenous cohort of rural Chinese villagers.

METHODS

Generalized estimating equations analysis was used to test for associations of systolic blood pressure (SBP) and diastolic blood pressure (DBP) with variants in 24 genes in BP pathways (196 single-nucleotide polymorphisms (SNPs)) among 3,142 Chinese participants divided according to physical activity (active vs. inactive groups).

RESULTS

In the physically active group, two SNPs in NR3C2 were significantly associated with lower SBP, and a SNP in SCNN1B was significantly associated with lower SBP and DBP. In the physically inactive group, a SNP in APLNR was associated with lower SBP, a SNP in GNB3 (guanine nucleotide binding protein, β polypeptide 3) was associated with higher SBP and DBP, and a SNP in BDKRB2 (bradykinin receptor B2) was associated with lower DBP. Cumulative effects in carriers of minor alleles of these SNPs showed reductions of SBP and DBP as large as 8 and 5 mm Hg, respectively, in the active individuals compared to inactive individuals carrying the same number of minor alleles.

CONCLUSIONS

We found that physical activity modifies the effects of genetic variants on BP. However, our results also show that active individuals with specific genotypes always have lower BP than inactive individuals with the same genotypes, demonstrating the overall beneficial effects of physical activity on BP.

SNPs in genes encoding G proteins in pharmacogenetics

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

The 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 G protein β3 subunit C825T polymorphism is associated with microalbuminuria in hypertensive women and cardiovascular disease in hypertensive men

BACKGROUND

The aim of the study was to examine the association between the G protein β3 subunit C825T polymorphism, associated with cardiovascular risk factors like hypertension (HT) and obesity and microalbuminuria (MA), reflecting the endothelial dysfunction in the atherosclerotic process. Second, we wanted to examine the association between the polymorphism and cardiovascular disease (CVD).

METHODS

In the large population-based, cross-sectional Nord-Trøndelag Health Study, HUNT 1995-1997, a total of 5,755 treated hypertensive individuals attended the MA substudy. A randomly selected sample of 1,000 of these was genotyped. A total of 402 men and 540 women were included in the final analyses. MA was measured as albumin/creatinine ratio (ACR) in three urine samples. Logistic regression was used to calculate odds ratios (ORs) for the association between MA or CVD and the genotype.

RESULTS

The study demonstrated a positive association between the TT genotype and MA in women (OR 3.2, 95% confidence interval (CI): 1.1-8.7, P = 0.03), but not in men. The association became stronger with increasing number of positive urine samples and with increasing cutoff value in women with TT genotype compared to the CC genotype. Additionally, there was a positive association between TT genotype and CVD in men and postmenopausal women without hormone therapy.

CONCLUSIONS

Increased MA in TT homozygous women might be explained by other mechanisms of albuminuria or inflammation than the atherosclerotic process. We postulate that the association between CVD and the genotype are mediated through mechanisms other than the classical risk factors and endothelial dysfunction, reflected by MA, which have to be further investigated.

The Influence of G‐Protein β3‐Subunit Gene and Endothelial Nitric Oxide Synthase Gene in Exon 7 Polymorphisms on Progression of Autosomal Dominant Polycystic Kidney Disease

BACKGROUND

A significant phenotypical variability is observed in autosomal dominant polycystic kidney disease (ADPKD). The variability cannot be fully explained by the genetic heterogeneity of the disease. We examined the influence of G-protein beta3-subunit C825T polymorphism and endothelial nitric oxide synthase Glu298Asp polymorphism on the progression of ADPKD towards end stage renal failure (ESRF).

METHODS

306 ADPKD patients (pts) were analyzed; 261 pts (136 males, 125 females) with ESRF, with subgroup of 73 pts (44 males, 29 females) with ESRF before 45 years (rapid progressors), 46 pts (20 males, 26 females) with ESRF later than in 63 years (slow progressors) and 45 ADPKD pts (17 males, 28 females) in mean age 51 years with serum creatinine under 110 micromol/L (slow progressors) and 100 genetically unrelated healthy Czech subjects. DNA samples from collected blood were genotyped for G-protein beta3-subunit C825T genotype in exon 10 and for endothelial nitric oxide synthase Glu298Asp genotype in exon 7.

RESULTS

The G-protein beta3-subunit C825T genotype exhibited no significant differences among the groups of slow progressors (6.6% (6/91) TT, 54.9% (50/91) CT, 38.8% (35/91) CC), rapid progressors (9.6% (7/73) TT, 46.6% (34/73) CT, 43.8% (32/73) CC), ADPKD group with ESRF between 40-63 years (9.2% (13/142) TT, 50% (71/142) CT, 40.8% (58/142) CC) and control group (12% TT, 44% CT, 44% CC). When comparing the ages of ESRF of all patients with ESRF, we did not find significant differences in the ages: males TT--51.7+/-8.8 years, CT--51.9+/-10.3 years, CC--49.7+/-10.2 years and females TT--56+/-9.9 years, CT--53.2+/-8.5 years, CC--53.9+/-8.7 years. The endothelial nitric oxide synthase Glu298Asp and Asp29Asp genotypes were significantly more frequent in rapid progressors (9.6% (7/73) Asp/Asp, 39.7% (29/73) Asp/Glu, 50.7% (37/73) Glu/Glu) and in ADPKD group with ESRF between 40-63 years (11.3% (16/142) Asp/Asp, 41.5% (59/142) Asp/Glu, 47.2% (67/142) Glu/Glu) in comparison with slow progressors (8.8% (8/91) Asp/Asp, 24.2% (22/91) Asp/Glu, 67.0% (61/91) Glu/Glu) and with control group (8% Asp/Asp, 32% Asp/Glu, 60% Glu/Glu) (Chi-square test, p<0.05). Comparing the ages of ESRF of all patients with ESRF, we did not find significant differences in the ages in males with Asp/Asp--54.9+/-10.4 years, Asp/Glu--50.2+/-9.4 years, Glu/Glu--51.0+/-10.4 years. We found out in homozygous Asp/Asp females significantly earlier onset of ESRF (49.2+/-5.6 years) in comparison with heterozygous females (53.3+/-7.2 years) and with Glu/Glu homozygous females (54.8+/-9.7 years) (t-test, p<0.05).

CONCLUSION

We excluded the significance of G-protein beta3-subunit C825T polymorphism on the progression of ADPKD. We established the negative prognostic value of the carriers of Asp variant of eNOS polymorphism. Finding of new modifiers could have in future clinical consequences for ADPKD patients.

Association study of the G-protein beta3 subunit C825T polymorphism with disease progression an overall survival in patients with head and neck squamous cell carcinoma

The T-allele of a common C825T single nucleotide polymorphism (SNP) in the gene GNB3, encoding the G3 subunit of heterotrimeric G-proteins, is associated with a truncated form of the G3 protein that imparts a greater signaling capacity than the alternative C-allele encoding a nontruncated protein. We analyzed the C825T-allele status with regard to disease progression in patients with head and neck squamous cell carcinoma (HNSCC). The prognostic value of the SNP was evaluated in an unselected series of 341 patients treated with curative intent for HNSCC including all tumor stages with different therapeutic regimens. Genotype analysis was done by Pyrosequencing using DNA from paraffin-embedded tissue samples. Genotypes were correlated with relapse-free and overall survival. Proportions of 5-year relapse-free intervals were 62% for CC, 60% for TC, and 42% for TT genotypes. Kaplan-Meier curves revealed a significant genotype-dependent relapse-free interval (P = 0.036). In multivariate analysis with stage, localization, grade, gender, and smoking habits as covariates, GNB3 825T homozygous patients displayed a higher risk for relapse than C825 homozygous patients (TT versus CC, hazard ratio; 95% confidence interval, 1.4-4.8; P = 0.002). The same genotype effect was found for overall survival, TT genotypes were at higher risk for death compared with CC genotypes (hazard ratio, 2.6; 95% confidence interval, 1.6-4.3; P < 0.001), and 5-year survival proportions were 60% for CC, 52% for TC, and 33% for TT. The GNB3 C825T SNP thus represents a host derived prognostic marker in HNSCC, which allows identifying high-risk patients, which could benefit from novel and/or more aggressive therapeutic regimes.

Association of antipsychotic induced weight gain and body mass index with GNB3 gene: a meta-analysis

It has been reported that C825T variant in the gene encoding the G-protein subunit beta3 (GNB3) is associated with antipsychotic-induced weight gain and obesity. We investigated the association of the GNB3 and antipsychotic-induced weight gain as well as body mass index (BMI) using meta-analytical techniques. Our analysis of 402 schizophrenia subjects showed a trend (p=0.072) only under a fixed-model. As it was observed heterogeneity among the studies (p=0.007), we re-analyzed using a random-effects framework and no significance was found (p=0.339). No evidence for bias publication was reported (p=0.868). Our analysis of 18,903 subjects showed a trend (p=0.053) associating CC and lower BMI under a fixed model. Although no significant association was found, the same pattern (CC and lower antipsychotic-induced weight gain) was observed. Our meta-analysis indicates that firmly establishing the role of pharmacogenetics in clinical psychiatry requires much larger sample sizes that have been reported.

Overall and relapse-free survival in oropharyngeal and hypopharyngeal squamous cell carcinoma are associated with genotypes of T393C polymorphism of the GNAS1 gene

PURPOSE

In previous studies, we have shown that the T allele of a specific single-nucleotide polymorphism (SNP) in the Galphas gene (T393C) correlates with increased Galphas expression and hence apoptosis. The T allele was associated with a favorable outcome in a variety of human cancers, e.g., carcinoma of the urinary bladder, kidney, and colorectum.

EXPERIMENTAL DESIGN

The prognostic value of the T393C SNP was evaluated in an unselected series of patients treated with curative intent for oropharyngeal and hypopharyngeal squamous cell carcinomas, including all tumor stages with different therapeutic regimens. Genotype analysis was done using DNA from paraffin-embedded tissue samples from 202 patients (162 men, 40 women) with a median follow-up of 38 months (1-133 months). The various genotypes were correlated with relapse-free and overall survival.

RESULTS

GNAS1 393C homozygous patients displayed a higher risk for disease progression than T393 homozygous patients (hazard ratio CC versus TT, 1.9; 95% confidence interval, 1.1-3.2; P = 0.019). The same genotype effect was observed for overall survival with CC genotypes at higher risk for death compared with TT genotypes (hazard ratio, 1.7; 95% confidence interval, 1.1-2.9; P = 0.015). Multivariate analysis showed that, besides American Joint Committee on Cancer stage, tumor localization, and gender, the T393C polymorphism was an independent prognostic factor for disease progression and death.

CONCLUSION

The T393C SNP could be considered as a genetic marker to predict the clinical course of patients suffering from oropharyngeal and hypopharyngeal cancer.

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.

The human obesity gene map: the 2005 update

This paper presents the 12th update of the human obesity gene map, which incorporates published results up to the end of October 2005. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, transgenic and knockout murine models relevant to obesity, quantitative trait loci (QTL) from animal cross-breeding experiments, association studies with candidate genes, and linkages from genome scans is reviewed. As of October 2005, 176 human obesity cases due to single-gene mutations in 11 different genes have been reported, 50 loci related to Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and causal genes or strong candidates have been identified for most of these syndromes. There are 244 genes that, when mutated or expressed as transgenes in the mouse, result in phenotypes that affect body weight and adiposity. The number of QTLs reported from animal models currently reaches 408. The number of human obesity QTLs derived from genome scans continues to grow, and we now have 253 QTLs for obesity-related phenotypes from 61 genome-wide scans. A total of 52 genomic regions harbor QTLs supported by two or more studies. The number of studies reporting associations between DNA sequence variation in specific genes and obesity phenotypes has also increased considerably, with 426 findings of positive associations with 127 candidate genes. A promising observation is that 22 genes are each supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. The electronic version of the map with links to useful publications and relevant sites can be found at http://obesitygene.pbrc.edu.

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.

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

AIMS/HYPOTHESIS

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSIONS/INTERPRETATION

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

The C allele of theGNB3 C825T polymorphism of the G protein β3-subunit is associated with an increased risk for the development of oncocytic thyroid tumours

Carriers of the C allele of the common C825T polymorphism in the GNB3 gene of the G protein have been associated with the development of follicular thyroid adenomas. Since the C allele of this polymorphism is related to a lower signalling capacity, it was speculated whether the C825T polymorphism may play a particular role in oncocytic thyroid tumours, which are recognized for their reduced ability to synthesize thyroid-specific proteins and hormones, although they possess an intact thyroid-stimulating hormone receptor-adenylyl cyclase system. Using pyrosequencing, both the genotype distribution and the allele frequency of the C825T polymorphism were investigated in a series of 104 patients with oncocytic thyroid tumours of follicular cell origin [58 adenomas, 41 follicular thyroid carcinomas (FTCs), and five papillary thyroid carcinomas (PTCs)]; the results were compared with those obtained from 321 age and gender-matched healthy blood donors and a series of 327 non-oncocytic thyroid tumours of follicular cell origin (119 adenomas, 80 FTCs, and 186 PTCs). Analysis of the genotype distribution (comparing oncocytic with non-oncocytic tumours of the present series) revealed a significantly increased odds ratio (OR) for CC versus TT (OR = 4.22; p = 0.011) and CC versus CT (OR = 1.62; p = 0.049) carriers to develop an oncocytic thyroid tumour; ORs to develop an oncocytic thyroid tumour were also increased comparing the genotype distribution between the group of oncocytic tumours and healthy controls for CC versus TT (OR = 3.73; p = 0.017) and CC versus all T carriers (OR = 1.56; p = 0.034). Oncocytic thyroid tumours as a group showed a statistically significant increase of the C-allele frequency when compared with all non-oncocytic tumours (p = 0.0039) as well as healthy blood donors (p = 0.017). The results strongly suggest that the C allele of the GNB3 C825T polymorphism of the G protein beta3-subunit is associated with an increased risk for the development of oncocytic thyroid tumours. This polymorphism may thus be considered a (co)factor favouring the development of oncocytic thyroid tumours, although the biological mechanism(s) underlying this association remain obscure.

Different genotype distribution of theGNB3 C825T polymorphism of the G protein β3 subunit in adenomas and differentiated thyroid carcinomas of follicular cell origin

A C825T polymorphism has been demonstrated in the GNB3 gene that encodes the Gbeta3 subunit of heterotrimeric G proteins. Due to enhanced G protein activation, the GNB3 825T allele is associated with an increased signal transduction activity. To elucidate a possible role in the development and course of thyroid tumours of follicular cell origin, C825T polymorphism genotypes and allele frequencies were investigated in a series of adenomas and differentiated carcinomas. Genotypes and the allele frequency of the Gbeta3 polymorphism were investigated in samples from 361 patients (all white Caucasians) with differentiated thyroid tumours of follicular cell origin [80 adenomas and 95 follicular (FTCs) and 186 papillary carcinomas (PTCs)]. The results were compared with those of 1859 healthy controls. Both the genotype distribution (p = 0.029) and the allele frequency (p = 0.028) of the adenoma group were statistically significantly different from those of the control group. Thyroid adenomas also differed for both parameters significantly from FTCs (p = 0.042 and 0.033, respectively) and PTCs (0.0018 and 0.0081, respectively), whereas no statistical difference was noted between the FTC and PTC groups. Although the biological significance of these observations remains obscure, the results are suggestive of a putative role for the GNB3 polymorphism in thyroid tumour development and/or progression. Further research has to elucidate if, and to what extent, this common germ-line variation influences the TSH-triggered signalling pathways responsible for thyroid function and proliferation.

Behavioral consequences of testing for obesity risk

OBJECTIVE

There is considerable hope that genetic susceptibility testing will motivate behavior that can prevent or reduce the risk of complex conditions such as obesity. This study examined potential behavioral consequences of such testing.

METHODS

Participants (n = 249) were randomly assigned to review one of four vignettes that asked them to imagine that they had been tested for their risk of becoming overweight or obese. The experimental factors were test type (genetic versus hormone test) and risk level (increased versus average risk for obesity). Study measures included behavioral intentions and perceived behavioral control related to eating a healthy diet, as well as weight locus of control.

RESULTS

Participants assigned to the increased risk conditions indicated greater intentions to eat a healthy diet compared with participants assigned to the average risk conditions (P < 0.02). There were significant interaction effects of risk x perceived behavioral control (P < 0.02) and risk x weight locus of control (P < 0.003) on dietary intentions. Individuals with low perceived behavioral control or an external weight locus of control who were told to imagine they were at average risk expressed significantly lower intentions to eat a healthy diet. A three-way interaction of body mass index, family history of overweight/obesity, and assigned risk level found the greatest effects of risk feedback among those who either had a family history or a higher body mass index (P < 0.007).

CONCLUSION

This study provides preliminary evidence that testing for susceptibility to obesity may motivate healthier behavior. However, some individuals may be susceptible to a false reassurance effect after receiving test results indicating a lack of increased risk.

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.

G-protein beta3-subunit gene 825T allele and hypertension: a longitudinal study in young grade I hypertensives

The 825T allele of the GNB3 gene has been associated with essential hypertension and obesity in cross-sectional studies. We have therefore planned a longitudinal cohort study to assess whether the GNB3 825T allele is predictive of blood pressure increase in young subjects with grade I hypertension. We genotyped at the GNB3 825 locus 461 participants of the Hypertension and Ambulatory Recording Venetia Study (HARVEST) study (age, 18 to 45 years) at low cardiovascular risk, according to 1999 ISH/WHO criteria. The study end point was eligibility for antihypertensive medication, that is, progression to grade II hypertension during the first year of observation or office systolic blood pressure > or =150 mm Hg and/or office diastolic blood pressure > or =95 mm Hg in two later consecutive visits during follow-up. At baseline, there was no statistically significant difference among genotypes with respect to body mass index, blood pressure, and heart rate. During follow-up (mean, 4.7 years), 113 (51.1%) patients with CC genotype and 145 (60.4%) patients with TT/TC genotype reached the end point. According to survival analysis, the patients carrying the 825T allele had an increased risk of reaching the blood pressure end point (CI, 1.108 to 1.843; P=0.006). In young patients with grade I hypertension, the 825T allele is associated with increased risk of progression to more severe hypertension requiring antihypertensive therapy. The GNB3 825T allele may be considered a genetic marker of predisposition for hypertension.

Prediction of successful weight reduction under sibutramine therapy through genotyping of the G-protein beta3 subunit gene (GNB3) C825T polymorphism

BACKGROUND

Sibutramine, a centrally acting noradrenaline and serotonin re-uptake inhibitor, enhances satiety and is frequently used to support weight loss. However, a significant variability exists among individuals concerning the response to sibutramine.

METHODS

We genotyped 111 participants of a randomized placebo-controlled clinical trial for the GNB3 C825T polymorphism and analysed associations of genotypes with treatment outcome. Patients undergoing a structured weight loss programme were treated with either placebo or 15 mg sibutramine daily for 54 weeks.

RESULTS

In the placebo group, the non-pharmacological programme alone resulted in a significantly greater weight loss in individuals with the GNB3 TT/TC genotypes as compared to individuals with the CC genotype (-7.1 +/- 1.2 vs. -2.7 +/- 1.5 kg, P = 0.031). Administration of 15 mg sibutramine was more effective in individuals with the CC genotype than in the subjects with the TT/TC genotypes (weight loss: 7.2 +/- 2.2 vs. 4.1 +/- 2.1 kg, P = 0.0013, sibutramine vs. placebo). In the CC genotype carriers, the odds ratio (OR) for a weight loss greater than 5% (sibutramine vs. placebo) was 6.6 (95% CI 1.8-25.6; P = 0.004) and for a weight loss greater than 10% was 9.6 (95% CI 1.7-53.8; P = 0.010).

CONCLUSION

Genotyping for the GNB3 C825T polymorphism is highly predictive for the identification of obese individuals who will benefit from sibutramine treatment.

Common genetic risk factors for psychiatric and simatic disorders

There is increasing knowledge about considerable comorbidity between psychiatric and somatic diseases, questioning whether variations in genes could be predisposing factors for both conditions. With respect to the multiple interactions between brain and body investigations have centered on variants in several candidate genes for proteins that mediate these interactions and therefore also have implications in psychiatric disorders. The available data, although still preliminary and rare, indicate the importance of polymorphic variants in genes coding for the serotonin (5-hydroxytryptamine, 5-HT) transporter (5-HTT), the 5-HT_2A receptor, proinflammatory cytokines, and the angiotensin-converting enzyme (ACE) in migraine, fibromyalgia, cardiovascular disorders, and psychiatric conditions. The role played by these various polymorphisms remains to be determined, as does whether they are indicative of common pathophysiological mechanisms or identify a subgroup of patients with somatic disorders that are more closely related to psychiatric symptoms. Nevertheless, they do at least illustrate the potential influence of genetic differences on illness course and treatment outcome, and might be a rational approach to drug development and treatment paradigms.

Metabolic and haemodynamic effects of oral glucose loading in young healthy men carrying the 825T-allele of the G protein beta3 subunit

BACKGROUND

A C825T polymorphism was recently identified in the gene encoding the beta3 subunit of heterotrimeric G-proteins (GNB3). The T-allele is significantly associated with essential hypertension and obesity. In order to further explore a possible pathogenetic link between the T-allele and impaired glucose tolerance we studied metabolic and haemodynamic responses to oral glucose loading in young, healthy subjects with and without the 825T-allele.

METHODS

Twelve subjects with and 10 without the 825T-allele were investigated at rest and following glucose ingestion (75 g). Blood glucose, serum insulin and haemodynamics were determined prior to and over 2 hours following glucose ingestion. We non-invasively measured stroke volume (SV, by impedance-cardiography), blood pressure (BP), heart rate (HR), and systolic-time-intervals. Cardiac output (CO) was calculated from HR and SV. Total peripheral resistance was calculated from CO and BP. Metabolic and haemodynamic changes were quantified by maximal responses and by calculation of areas under the concentration time profile (AUC). Significances of differences between subjects with and without the T-allele were determined by unpaired two-tailed t-tests. A p < 0.05 was considered statistically significant.

RESULTS

Metabolic and haemodynamic parameters at baseline were very similar between both groups. The presence of the T-allele did not alter the response of any metabolic or haemodynamic parameter to glucose loading.

CONCLUSIONS

In conclusion, this study does not support the hypothesis that the C825T polymorphism may serve as a genetic marker of early impaired glucose tolerance.

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.

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.

The human obesity gene map: the 2002 update

This is the ninth update of the human obesity gene map, incorporating published results through October 2002 and continuing the previous format. Evidence from single-gene mutation obesity cases, Mendelian disorders exhibiting obesity as a clinical feature, quantitative trait loci (QTLs) from human genome-wide scans and various animal crossbreeding experiments, and association and linkage studies with candidate genes and other markers is reviewed. For the first time, transgenic and knockout murine models exhibiting obesity as a phenotype are incorporated (N = 38). As of October 2002, 33 Mendelian syndromes relevant to human obesity have been mapped to a genomic region, and the causal genes or strong candidates have been identified for 23 of these syndromes. QTLs reported from animal models currently number 168; there are 68 human QTLs for obesity phenotypes from genome-wide scans. Additionally, significant linkage peaks with candidate genes have been identified in targeted studies. Seven genomic regions harbor QTLs replicated among two to five studies. Attempts to relate DNA sequence variation in specific genes to obesity phenotypes continue to grow, with 222 studies reporting positive associations with 71 candidate genes. Fifteen such candidate genes are supported by at least five positive studies. The obesity gene map shows putative loci on all chromosomes except Y. More than 300 genes, markers, and chromosomal regions have been associated or linked with human obesity phenotypes. The electronic version of the map with links to useful sites can be found at http://obesitygene.pbrc.edu.

Genetics of blood pressure, hypertensive complications, and antihypertensive drug responses

Hypertension is the most prevalent, treatable risk factor for diseases of the heart, brain and kidneys. In this review, we discuss advances in understanding of the genetics of blood pressure regulation, the development of hypertensive complications and the pharmacodynamics of antihypertensive drug responses. Discovery of single gene mutations that cause hypertension or hypotension in humans suggests that the common final pathway for regulation of blood pressure level is via alterations in renal sodium handling. Based on a working hypothesis that common genetic variations contributing to blood pressure variation in the population may also act on this same pathway, we summarize supporting evidence emerging from linkage and selected association studies of candidate genes--including those encoding components of the renin-angiotensin-aldosterone system, the epithelial sodium channel, adrenoceptors, G protein subunits, and other cellular signaling mediators and modifiers. We proceed to distinguish ischemic target organ complications due to arteriolosclerotic changes of the microvasculature from those due to atherosclerosis involving larger conduit and capacitance arteries. Using the example of subcortical white matter ischemia of the brain, we propose that interindividual variation in the arteriolosclerotic complications is more likely than atherosclerotic complications to be related to the same genetic (and environmental) mechanisms that contribute to hypertension. We conclude by summarizing the state-of-the-art of antihypertensive pharmacogenetics, which has succeeded in rejecting the null hypothesis that genetic variation does not influence blood pressure or protective target organ responses to drug therapy. In each of the three areas covered in this review, we indicate the many remaining obstacles to the routine clinical use of genetic measurements in the diagnosis, evaluation and treatment of hypertension.

Identification of hypertension-related QTLs in African American sib pairs

To link hypertension-related phenotypes with chromosomal loci, genome scans were performed in 150 African American sib pairs concordant for essential hypertension. Phenotypes included blood pressure, anthropomorphic measurements, and estimates of body fluid compartments as determined by impedance plethysmography. These phenotypes were also measured in 335 normotensive African Americans. Phenotypes with LOD scores >3.3 were further evaluated for significance by use of permutation procedures. Significant linkage was detected for body mass index (BMI) on chromosomes 1 and 8 and for the ratio of extracellular water to total body water (ECF/TBW) on chromosomes 3, 5, 6, and 7. Both BMI and ECF/TBW were greater in hypertensive sibs than in normotensive subjects (P<0.001). In a subset of hypertensive sibs and normotensive subjects, average 24-hour blood pressures were correlated with ECF/TBW (P<0.01). A region linked to BMI in the hypertensive sibs corresponds to a region of conserved synteny containing blood pressure-related QTLs in an F2 cross of Brown NorwayxDahl salt-sensitive rats. Focusing on hypertension-related phenotypes is a promising approach for identifying the genetic determinants of hypertension.

Enhanced vasoconstriction to endothelin-1, angiotensin II and noradrenaline in carriers of the GNB3 825T allele in the skin microcirculation

Hypertension is associated with enhanced peripheral vascular resistance, which may be mediated by enhanced vasoconstriction. The impact of the recently detected G-protein beta3-subunit gene C825T polymorphism on the response to the major pressor mediators has been studied in vivo in the human microcirculation. We assessed the effects of endothelin-1 (ET-1), angiotensin II (AT), endothelin-antagonists (BQ-123 and BQ-788) and noradrenaline (NA, each 10-16-10-8 mol) on vasoconstriction in the human skin microcirculation in vivo in 25 healthy male volunteers (13 with CC genotype, 12 TC/TT genotype) using laser Doppler flowmetry. The effects of endothelium-derived vasodilation on NA-induced effects were studied using the NO-synthase inhibitor l-nitro-monomethyl-arginine (L-NMMA) and the alpha2-adrenoceptor-antagonist yohimbine (YO). ET-1, AT and NA caused a dose-dependent vasoconstriction (P < 0.001). In carriers of the 825T allele the response to ET-1, AT and NA was significantly enhanced leading to a shift to the left of the dose-response curve of up to two log units (ET-1: P < 0.001 vs. CC; AT: P < 0.01 vs. CC; NA: P < 0.05 vs. CC). After pretreatment with L-NMMA or YO, NA induced vasoconstriction was no longer different between subjects with the CC- and CT/TT genotypes. However, following combined pretreatment with both L-NMMA and YO, vasoconstriction to NA was significantly potentiated in carriers of the T-allele. Vasodilatation to an ETA-antagonist (BQ-123) was more pronounced in the CT/TT genotype, while ETB-antagonism (BQ-788) led to a more pronounced vasoconstriction in the CT/TT genotype (not significant vs. CC). Healthy, normotensive carriers of the 825T-allele have enhanced vasoconstriction to ET-1, AT and NA in the skin microcirculation. This enhanced vasoconstriction appears to be partially antagonized by an enhanced release of endothelium derived vasodilators mediated by the stimulation of endothelial alpha2-adrenoceptors. The GNB3 C825T polymorphism is potentially an attractive pharmacogenetic marker to predict hormone-mediated responses in humans.

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.

A genealogical study of essential hypertension with and without obesity in French Canadians

OBJECTIVES

To investigate genetic homogeneity in a set of hypertensive families and in subsets chosen for high and low prevalence of obesity; and to compare fasting insulin and lipids, ion transport, and water homeostasis in the obese and lean families.

RESEARCH METHODS AND PROCEDURES

The study was carried out in a relative population isolate of the Saguenay/Lac St. Jean region in Canada. Genetic homogeneity was evaluated with the mean coeffigcients of kinship (phi) and inbreeding (F) computed with ascending genealogies. Serum insulin and lipids were measured after overnight fasting. Total body water was estimated with bioelectrical impedance. Sodium-lithium countertransport and sodium-potassium co-transport were determined in freshly isolated erythrocytes.

RESULTS

F and phi were increased in hypertensive families compared with families selected at random. F and phi were further increased within the subsets of obese and lean families. In addition, fasting insulin, total body water, sodium-lithium countertransport, and sodium-potassium co-transport were higher in the obese than in the lean families. The two subsets of families did not differ by fasting lipids.

DISCUSSION

In the Saguenay/Lac St. Jean population, the degree of genetic homogeneity was increased in families selected for hypertension, and it was further increased in subsets of hypertensive families with high and low prevalence of obesity. This suggests that hypertension in lean and obese individuals may represent, at least in part, separate genetic entities. Some of the extra genes shared in common within the subsets may contribute to their differences in body weight, insulin sensitivity, ion transport, and water homeostasis.

Physical activity does not mitigate G-protein-related genetic risk for obesity in individuals of African descent

The G-protein beta3 subunit 825 TT genotype has been associated with obesity and hypertension. We examined the interaction between the G-protein TT genotype, physical activity and body mass index (BMI) in a cross-sectional study of African immigrants and African Americans. The genotype frequencies were 6.3% CC, 37.7% CT, and 56% TT. After adjusting for potential confounders, BMI was found to be significantly higher in the sedentary than in the physically active participants (p=0.045). There was no statistically significant effect for genotype (p=0.215) or the interaction between genotype and the level of physical activity (p=0.219). However, the individuals with the CC or CT genotype who were physically active had substantially lower BMIs (M+/-SE) (i.e., 25.74+/-2.02) than any of the other groups: sedentary CC + CT (30.58+/-1.03), sedentary TT (30.65+/-1.00) or active TT (29.43+/-1.65). Because of the low statistical power of this study, further research is needed to confirm these findings and to explore potential gene-environment/lifestyle interactions.

The human obesity gene map: the 2001 update

This report constitutes the eighth update of the human obesity gene map, incorporating published results up to the end of October 2001. Evidence from the rodent and human obesity cases caused by single-gene mutations, Mendelian disorders exhibiting obesity as a clinical feature, quantitative trait loci (QTLs) uncovered in human genome-wide scans and in crossbreeding experiments in various animal models, association and linkage studies with candidate genes and other markers is reviewed. The human cases of obesity related in some way to single-gene mutations in six different genes are incorporated. Twenty-five Mendelian disorders exhibiting obesity as one of their clinical manifestations have now been mapped. The number of different QTLs reported from animal models currently reaches 165. Attempts to relate DNA sequence variation in specific genes to obesity phenotypes continue to grow, with 174 studies reporting positive associations with 58 candidate genes. Finally, 59 loci have been linked to obesity indicators in genomic scans and other linkage study designs. The obesity gene map depicted in Figure 1 reveals that putative loci affecting obesity-related phenotypes can be found on all chromosomes except chromosome Y. A total of 54 new loci have been added to the map in the past 12 months, and the number of genes, markers, and chromosomal regions that have been associated or linked with human obesity phenotypes is now above 250. Likewise, the number of negative studies, which are only partially reviewed here, is also on the rise.

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.

Use of gene markers to guide antihypertensive therapy

Sequencing of the human genome has elevated the potential for genetic information to aid in the prevention, diagnosis, and treatment of common chronic diseases. One beneficial application of genetic information is the identification of variants that influence response to pharmaceutical agents used to lower blood pressure and prevent target organ complications of hypertension. Knowledge of genetic variants that influence blood pressure response to antihypertensive drugs may allow more individualized tailoring of antihypertensive drug therapy, and provide greater insight into the molecular mechanisms regulating blood pressure levels and causing hypertension.

Analysis of 825C/T polymorphism of G proteinbeta3 subunit in obese/diabetic Japanese

The GNB3 825C/T polymorphism, which is common worldwide, is associated with enhanced G-protein activation. The frequency of 825-T allele was increased with body mass index (BMI) and finally had a high frequency in relatively mild obese (BMI >27 kg/m(2)) subjects in some populations. In the present study, we investigated 208 severely obese [BMI >or=30 kg/m(2) (97th percentile)] Japanese subjects including 146 probands with diabetes. No increase in the 825-T allele frequency was observed in the 208 severely obese and even in a subgroup of the 55 most obese [BMI >or=35 kg/m(2) (99.7th percentile)] subjects compared with that in 150 controls (BMI <25 kg/m(2)) (0.48 and 0.48 vs 0.51, respectively). Also, the frequency was not increased in the 146 obese subjects with diabetes (0.48). We concluded that the 825-T allele is not associated with obesity or diabetes associated with obesity at least in the Japanese population.

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.