Association between β-adrenergic receptor polymorphisms and their G-protein-coupled receptors with body mass index and obesity in women: a report from the NHLBI-sponsored WISE study

Effect of β3-adrenergic receptor gene polymorphism and lifestyle on overweight Japanese rural residents: A cross-sectional study

Objectives

The β3-adrenergic receptor (ADRB3) gene polymorphism has been implicated in obesity. Therefore, the contribution of ADRB3 Trp64Arg polymorphism to obesity-related indicators was investigated, taking into account the lifestyle-related factors in a Japanese rural population.

Methods

A total of 600 Japanese adults aged ≥40 years in a population-based cohort study were analyzed. The ADRB3 polymorphism was determined using peripheral blood samples. Associations between genotype and body mass index (BMI), waist circumference (WC), and body fat (BF) percentage were examined, adjusting for lifestyle-related factors, including daily nutrient intake.

Results

The frequency of Arg64 allele carriers was 36%. There was no significant difference in BMI, WC, or BF between the groups with or without the Trp64Arg polymorphism. Multivariable logistic regression analysis showed that the Trp64Arg polymorphism was not associated with these three indicators, but lifestyle factors including physical inactivity, higher energy and sodium consumption, and less animal protein intake were significantly related to increased WC and BF percentages.

Conclusions

The Trp64Arg polymorphism of ADRB3 gene did not contribute to increased BMI, WC, or BF. However, lifestyle-related factors impacted these indicators in middle-aged and older Japanese individuals living in rural areas.

Association Between Trp64arg Polymorphism of the β3 adrenoreceptor Gene and Female Sex in Obese Turkish Children and Adolescents

PURPOSE

The β3-adrenergic receptor (ADRB3) is expressed in visceral adipose tissue and has been speculated to contribute to lipolysis, energy metabolism, and regulation of the metabolic rate. In this study, we aimed to investigate the association of polymorphism of the ADRB3 gene with the sex of children with obesity and related pathologies.

METHODS

ADRB3 gene trp64arg genotyping was conducted in 441 children aged 6-18 years. Among these subjects, 264 were obese (103 boys; 161 girls) and 179 were of normal weight (81 boys; 98 girls). In the obese group, fasting lipids, glucose and insulin levels, and blood pressure were measured. Metabolic syndrome (MS) was defined according to the modified World Health Organization criteria adapted for children.

RESULTS

The frequency of trp64arg genotype was similar in obese and normal weight children. In obese children, serum lipid, glucose, and insulin levels; homeostasis model assessment of insulin resistance (HOMA-IR) scores; and MS were not different between arg allele carriers (trp64arg) and noncarriers (trp64trp). In 264 obese children, genetic analysis results revealed that the arg allele carriers were significantly higher in girls than in boys (p=0.001). In the normal weight group, no statistically significant difference was found between genotypes of boys and girls (p=0.771).

CONCLUSION

Trp64arg polymorphism of the ADRB3 gene was not associated with obesity and MS in Turkish children and adolescents. Although no relationships were observed between the genotypes and lipids, glucose/insulin levels, or HOMA-IR, the presence of trp64arg variant was frequent in obese girls, which can lead to weight gain as well as difficulty in losing weight in women.

Attenuated atrial natriuretic peptide-mediated lipolysis in subcutaneous adipocytes of obese type 2 diabetic men

Subjects with obesity seem to display a suboptimal exercise response, which might be due to hormonal disturbances. In the present study, we show the adipose tissue of obese subjects to be less sensitive to atrial natriuretic peptide, a cardiac hormone important during exercise.

Association of Gln27Glu and Arg16Gly polymorphisms in Beta2-adrenergic receptor gene with obesity susceptibility: a meta-analysis

BACKGROUND

The beta2-adrenergic receptor (ADRB2) gene polymorphism has been implicated in susceptibility to obesity, but study results are still controversial.

OBJECTIVE

The present meta-analysis is performed to determine whether there are any associations between the Gln27Glu (rs1042714) or the Arg16Gly (rs1042713) polymorphisms in ADRB2 and obesity susceptibility.

METHODS

The PubMed (1950-2014), Embase (1974-2014), and China National Knowledge Infrastructure (CNKI, 1994-2014) databases were searched using the search terms ("Beta2-adrenergic receptor", "β2-adrenergic receptor" or "ADRB2"), "polymorphism," and "obesity". Fixed- or random-effects pooled measures were determined on the bias of heterogeneity tests across studies. Publication bias was examined by Egger's test and the modified Begg's test.

RESULTS

Eighteen published articles were selected for meta-analysis. Overall analyses showed that rs1042714 (Gln27Glu) was associated with significantly increased obesity risk in the heterozygote model (Gln/Glu vs. Gln/Gln: OR: 1.16, 95% CI: 1.04-1.30, I2 = 49%, P = 0.009) and the dominant model (Gln/Glu + Glu/Glu vs. Gln/Gln: OR: 1.2, 95% CI: 1.00-1.44, I2 = 55%, P = 0.04), whereas no significant association was found in the other models for rs1042714. Also, no significant association was found between the rs1042713 (Arg16Gly) gene polymorphism and the risk of obesity in all genetic models. In addition, neither rs1042713 (Arg16Gly) nor rs1042714 (Gln27Glu) showed any significant association with obesity susceptibility when the population were stratified based on gender.

CONCLUSION

Our meta-analysis revealed that the rs1042714 (Gln27Glu) polymorphism is associated with obesity susceptibility. However, our results do not support an association between rs1042713 (Arg16Gly) polymorphisms and obesity in the populations investigated. This conclusion warrants confirmation by more case-control and cohort studies.

Regulation of adipocyte lipolysis

In adipocytes the hydrolysis of TAG to produce fatty acids and glycerol under fasting conditions or times of elevated energy demands is tightly regulated by neuroendocrine signals, resulting in the activation of lipolytic enzymes. Among the classic regulators of lipolysis, adrenergic stimulation and the insulin-mediated control of lipid mobilisation are the best known. Initially, hormone-sensitive lipase (HSL) was thought to be the rate-limiting enzyme of the first lipolytic step, while we now know that adipocyte TAG lipase is the key enzyme for lipolysis initiation. Pivotal, previously unsuspected components have also been identified at the protective interface of the lipid droplet surface and in the signalling pathways that control lipolysis. Perilipin, comparative gene identification-58 (CGI-58) and other proteins of the lipid droplet surface are currently known to be key regulators of the lipolytic machinery, protecting or exposing the TAG core of the droplet to lipases. The neuroendocrine control of lipolysis is prototypically exerted by catecholaminergic stimulation and insulin-induced suppression, both of which affect cyclic AMP levels and hence the protein kinase A-mediated phosphorylation of HSL and perilipin. Interestingly, in recent decades adipose tissue has been shown to secrete a large number of adipokines, which exert direct effects on lipolysis, while adipocytes reportedly express a wide range of receptors for signals involved in lipid mobilisation. Recently recognised mediators of lipolysis include some adipokines, structural membrane proteins, atrial natriuretic peptides, AMP-activated protein kinase and mitogen-activated protein kinase. Lipolysis needs to be reanalysed from the broader perspective of its specific physiological or pathological context since basal or stimulated lipolytic rates occur under diverse conditions and by different mechanisms.

G protein-coupled receptor accessory proteins and signaling: pharmacogenomic insights

The identification and characterization of the genes encoding G protein-coupled receptors (GPCRs) and the proteins necessary for the processes of ligand binding, GPCR activation, inactivation, and receptor trafficking to the membrane are discussed in the context of human genetic disease. In addition to functional GPCR variants, the identification of genetic disruptions affecting proteins necessary to GPCR functions have provided insights into the function of these pathways. Gsα and Gβ subunit polymorphisms have been found to result in complex phenotypes. Disruptions in accessory proteins that normally modify or organize heterotrimeric G-protein coupling may also result in disease states. These include the contribution of variants of the regulator of G protein signaling (RGS) protein to hypertension; the role variants of the activator of G protein signaling (AGS) proteins to phenotypes (such as the type III AGS8 variant to hypoxia); the contribution of G protein-coupled receptor kinase (GRK) proteins, such as GRK4, in disorders such as hypertension. The role of accessory proteins in GPCR structure and function is discussed in the context of genetic disorders associated with disruption of the genes that encode them. An understanding of the pharmacogenomics of GPCR and accessory protein signaling provides the basis for examining both GPCR pharmacogenetics and the genetics of monogenic disorders that result from disruption of given receptor systems.

ADRB2 haplotype is associated with glucose tolerance and insulin sensitivity in obese postmenopausal women

The β(2)-adrenergic receptor (ADRB2) mediates obesity, cardiorespiratory fitness, and insulin resistance. We examined the hypothesis that ADRB2 Arg16Gly-Gln27Glu haplotype is associated with body composition, glucose tolerance, and insulin sensitivity in obese, postmenopausal women. Obese (>35% body fat), postmenopausal (age 45-75 years) women (n = 123) underwent genotyping, dual-energy X-ray absorptiometry, and computed tomography scans, exercise testing (VO(2(max))), 2-h oral glucose tolerance tests (OGTTs), and hyperinsulinemic-euglycemic clamps (80 mU/m(2)/min). Analysis of covariance (ANCOVA) tested for differences among haplotypes, with race, % body fat, and VO(2(max)) as covariates. We found that ADRB2 haplotype was independently associated with % body fat, abdominal fat distribution, VO(2(max)), insulin sensitivity (M/ΔInsulin), and glucose tolerance (ANOVA, P < 0.05 for all). Women homozygous for Gly16-Gln27 haplotype had the highest % body fat (52.7 ± 1.9%), high abdominal fat, low M/ΔInsulin (0.49 ± 0.08 mg/kg/min/pmol/l/10(2)), and impaired glucose tolerance (IGT) during an OGTT (G(120) = 10.2 ± 0.9 mmol/l). Women homozygous for Gly16-Glu27 haplotype also had low M/ΔInsulin (0.51 ± 0.05 mg/kg/min/pmol/l/10(2)) and IGT (G(120) = 8.2 ± 0.7 mmol/l). Subjects with Arg16-Gln27/Gly16-Gln27 haplotype combination had the highest VO(2(max)) (1.84 ± 0.07 l/min) and M/ΔInsulin (0.7 ± 0.04 mg/kg/min/pmol/l/10(2)), and normal glucose tolerance (G(120) = 6.4 ± 0.4 mmol/l), despite being obese. These data show associations of the ADRB2 Arg16Gly-Gln27Glu haplotype with VO(2(max)) and body composition, and an independent association with glucose metabolism, which persists after controlling for body composition and fitness. This suggests that ADRB2 haplotypes may mediate insulin action, glucose tolerance, and potentially risk for type 2 diabetes mellitus (T2DM) in obese, postmenopausal women.

Genetic variation in female BMI increases with number of children born but failure to replicate association between GNbeta3 variants and increased BMI in parous females

Objective:As post-pregnancy weight retention in women is a risk factor for obesity later in life, we assessed the changes in magnitude of genetic and environmental variation in BMI due to parity in an Australian female sample, comprising 11,915 female twins and their sisters.Results:Total variance of BMI increased with parity, primarily driven by an increase in nonadditive genetic variance. This finding was of particular interest given Gutersohn et al's (2000) report of recessive association between post-partum weight retention and the 825T allele of theGNβ3gene (rs5443) at 12p13.31. Hence, we attempted to replicate this association and test an additional three SNPs also located near or onGNβ3(rs10744716 (upstream), rs5442 (exon 10), rs5446 (exon 11)) in a sample of 3131 females and 1693 males from 2585 twin families. No association was found between these SNPs among females, even when allowing for a genotype by parity effect. However, a significant association was observed among males for rs10744716 (χ22= 10.22,p= 0.006; effect size = 0.47kg/m2), representing a novel association between a region upstream ofGNβ3and male BMI.

Using linkage analysis to identify quantitative trait loci for sleep apnea in relationship to body mass index

To understand the genetics of sleep apnea, we evaluated the relationship between the apnea hypopnea index (AHI) and body mass index (BMI) through linkage analysis to identify genetic loci that may influence AHI and BMI jointly and AHI independent of BMI. Haseman-Elston sibling regression was conducted on AHI, AHI adjusted for BMI and BMI in African-American and European-American pedigrees. A comparison of the magnitude of linkage peaks was used to assess the relationship between AHI and BMI. In EAs, the strongest evidence for linkage to AHI was on 6q23-25 and 10q24-q25, both decreasing after BMI adjustment, suggesting loci with pleiotropic effects. Also, a promising area of linkage to AHI but not BMI was observed on 6p11-q11 near the orexin-2 receptor, suggesting BMI independent pathways. In AAs the strongest evidence of linkage for AHI after adjusting for BMI was on chromosome 8p21.3 with linkage increasing after BMI adjustment and on 8q24.1 with linkage decreasing after BMI adjustment. Novel linkage peaks were also observed in AAs to both BMI and AHI on chromosome 13 near the serotonin-2a receptor. These analyses suggest genetic loci for sleep apnea that operate both independently of BMI and through BMI-related pathways.

beta-adrenergic receptor gene polymorphisms and beta-blocker treatment outcomes in hypertension

Numerous studies have demonstrated that beta(1)- and beta(2)-adrenergic receptor gene (ADRB1 and ADRB2) variants influence cardiovascular risk and beta-blocker responses in hypertension and heart failure. We evaluated the relationship between ADRB1 and ADRB2 haplotypes, cardiovascular risk (death, nonfatal myocardial infarction (MI), and nonfatal stroke), and atenolol-based vs. verapamil sustained-release (SR)-based antihypertensive therapy in 5,895 coronary artery disease (CAD) patients. After an average of 2.8 years, death rates were higher in patients carrying the ADRB1 Ser49-Arg389 haplotype (hazard ratio (HR) 3.66, 95% confidence interval (95% CI) 1.68-7.99). This mortality risk was significant in patients randomly assigned to verapamil SR (HR 8.58, 95% CI 2.06-35.8) but not atenolol (HR 2.31, 95% CI 0.82-6.55), suggesting a protective role for the beta-blocker. ADRB2 haplotype associations were divergent within the treatment groups but did not remain significant after adjustment for multiple comparisons. ADRB1 haplotype variation is associated with mortality risk, and beta-blockers may be preferred in subgroups of patients defined by ADRB1 or ADRB2 polymorphisms.

Pharmacogenetics of ophthalmic topical beta-blockers

Glaucoma is the second leading cause of blindness worldwide. The primary glaucoma risk factor is elevated intraocular pressure. Topical beta-blockers are affordable and widely used to lower intraocular pressure. Genetic variability has been postulated to contribute to interpersonal differences in efficacy and safety of topical beta-blockers. This review summarizes clinically significant polymorphisms that have been identified in the beta-adrenergic receptors (ADRB1, ADRB2 and ADRB3). The implications of polymorphisms in CYP2D6 are also discussed. Although the candidate-gene approach has facilitated significant progress in our understanding of the genetic basis of glaucoma treatment response, most drug responses involve a large number of genes, each containing multiple polymorphisms. Genome-wide association studies may yield a more comprehensive set of polymorphisms associated with glaucoma outcomes. An understanding of the genetic mechanisms associated with variability in individual responses to topical beta-blockers may advance individualized treatment at a lower cost.

Adrenergic gene polymorphisms and cardiovascular risk in the NHLBI-sponsored Women's Ischemia Syndrome Evaluation

BACKGROUND

Adrenergic gene polymorphisms are associated with cardiovascular and metabolic phenotypes. We investigated the influence of adrenergic gene polymorphisms on cardiovascular risk in women with suspected myocardial ischemia.

METHODS

We genotyped 628 women referred for coronary angiography for eight polymorphisms in the alpha1A-, beta1-, beta2- and beta3-adrenergic receptors (ADRA1A, ADRB1, ADRB2, ADRB3, respectively), and their signaling proteins, G-protein beta 3 subunit (GNB3) and G-protein alpha subunit (GNAS). We compared the incidence of death, myocardial infarction, stroke, or heart failure between genotype groups in all women and women without obstructive coronary stenoses.

RESULTS

After a median of 5.8 years of follow-up, 115 women had an event. Patients with the ADRB1 Gly389 polymorphism were at higher risk for the composite outcome due to higher rates of myocardial infarction (adjusted hazard ratio [HR] 3.63, 95% confidence interval [95%CI] 1.17-11.28; Gly/Gly vs. Arg/Arg HR 4.14, 95%CI 0.88-19.6). The risk associated with ADRB1 Gly389 was limited to those without obstructive CAD (n = 400, Pinteraction = 0.03), albeit marginally significant in this subset (HR 1.71, 95%CI 0.91-3.19). Additionally, women without obstructive CAD carrying the ADRB3 Arg64 variant were at higher risk for the composite endpoint (HR 2.10, 95%CI 1.05-4.24) due to subtle increases in risk for all of the individual endpoints. No genetic associations were present in women with obstructive CAD.

CONCLUSION

In this exploratory analysis, common coding polymorphisms in the beta1- and beta3-adrenergic receptors increased cardiovascular risk in women referred for diagnostic angiography, and could improve risk assessment, particularly for women without evidence of obstructive CAD.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00000554.

Pharmacogenomics of G protein-coupled receptor signaling: insights from health and disease

The identification and characterization of the processes of G protein-coupled receptor (GPCR) activation and inactivation have refined not only the study of the GPCRs but also the genomics of many accessory proteins necessary for these processes. This has accelerated progress in understanding the fundamental mechanisms involved in GPCR structure and function, including receptor transport to the membrane, ligand binding, activation and inactivation by GRK-mediated (and other) phosphorylation. The catalog of G(s)alpha and Gbeta subunit polymorphisms that result in complex phenotypes has complemented the effort to catalog the GPCRs and their variants. The study of the genomics of GPCR accessory proteins has also provided insight into pathways of disease, such as the contributions of regulator of G protein signaling (RGS) protein to hypertension and activator of G protein signaling (AGS) proteins to the response to hypoxia. In the case of the G protein-coupled receptor kinases (GRKs), identified originally in the retinal tissues that converge on rhodopsin, proteins such as GRK4 have been identified that have been subsequently associated with hypertension. Here, we review the structure and function of GPCR and associated proteins in the context of the gene families that encode them and the genetic disorders associated with their altered function. An understanding of the pharmacogenomics of GPCR signaling provides the basis for examining the GPCRs disrupted in monogenic disease and the pharmacogenetics of a given receptor system.

Beta-1 and beta-2 adrenoceptor polymorphisms: functional importance, impact on cardiovascular diseases and drug responses

Beta-1 and beta-2 adrenoceptors (AR) play a pivotal role in regulation of the activity of the sympathetic nervous system and agonists and antagonists at both beta AR subtypes are frequently used in treatment of cardiovascular diseases. Both beta-1 and beta-2 AR genes have several polymorphisms that encode different amino acids. This review summarizes new insights into the functional importance of these polymorphisms, as well as their relationship to cardiovascular diseases and their impact on responses to adrenergic drug treatment. At present, it seems that, for cardiovascular diseases, beta-1 and beta-2 AR polymorphisms do not play a role as disease-causing genes; they might, however, be associated with disease-related phenotypes. In addition they could influence adrenergic drug responses. Thus, the Arg389Gly beta-1 AR polymorphism might predict responsiveness to beta-1 AR agonist and blocker treatment: patients homozygous for the Arg389 beta-1 AR polymorphism should be good responders, while patients homozygous for the Gly389 beta-1 AR polymorphism should be poor or nonresponders. Furthermore, the Arg16Gln27 beta-2 AR seems to have strong impact on long-term agonist-induced beta-2 AR desensitization. Thus, patients carrying this haplotype appear to suffer from rapid loss of therapeutic efficacy of chronic agonist treatment, as has been demonstrated in asthma patients. Moreover, the Arg16Gln27 beta-2 AR haplotype might have some predictive value for poor outcome of heart failure. Future large prospective studies have to replicate these findings in order to reach the final goal of pharmacogenomic research: to optimize and individualize drug therapy based on the patient's genetic determinants of drug efficacy.

Association analyses of adrenergic receptor polymorphisms with obesity and metabolic alterations

Genes involved in the regulation of catecholamine function may be important in obesity because of the role catecholamines play in energy expenditure and lipolysis. To determine if common single nucleotide polymorphisms (SNPs) in beta(1)-adrenergic receptor (ADRB1), beta(2)-adrenergic receptor (ADRB2), beta(3)-adrenergic receptor (ADRB3), and alpha(2)-adrenergic receptor (ADRA2A) genes associate with obesity and metabolic alterations, we recruited 74 healthy African American and 161 white men and women (age, 18-49 years) to participate in this case-control genetic association study. Genotypes were determined by polymerase chain reaction and restriction fragment length polymorphism. Associations between genotype and body mass index (BMI), percentage of body fat (by measuring skinfold thickness in 7 different sites), fasting (12-hour) plasma glucose, insulin, potassium concentrations, glycated hemoglobin, and insulin resistance (homeostasis model assessment [HOMA(IR)] score) were performed. Among whites, the ADRB1 Arg389-->Gly variant associated with insulin concentrations and HOMA(IR): mean +/- SD values for insulin and HOMA(IR) in Arg389 homozygotes and carriers of the Gly were 10 +/- 7.0 and 12 +/- 9.4 micro IU/mL (P = .02) and 2.1 +/- 1.7 and 2.6 +/- 2.2 (P = .057), respectively. Systolic blood pressure was higher in whites for carriers of the ADBR1 Ser49 compared to Gly49 homozygotes (124 +/- 12.6 vs 119 +/- 11.3 mm Hg, respectively; P = .02). Subsequent analysis revealed that these associations were attributable to a higher BMI among obese participants. The ADRA2A G1780A SNP associated with BMI and percentage of body fat in African Americans (P = .05). Interactions were detected between ADRA2A C-1291G and ADRB2 Gln27-->Glu variants for obesity in African Americans and between ADRA2A C-1291G SNP and ADBR1 haplotype for obesity in whites. We conclude that common SNPs in adrenergic receptor genes may be important susceptibility loci for obesity and related alterations. Because of the limited size of our populations, our results should be interpreted with caution and should be replicated in larger populations.

Studies of associations between the Arg389Gly polymorphism of the beta1-adrenergic receptor gene (ADRB1) and hypertension and obesity in 7677 Danish white subjects

AIMS

Activation of the beta(1)-adrenergic receptor (ADRB1) causes increased lipolysis in adipose tissue and enhances cardiac output. Analysis of the association of the functional ADRB1 Arg389Gly variant with obesity and hypertension has given ambiguous results. To clarify the potential impact of this variant on obesity and hypertension in the general population, we examined the Arg389Gly variant in a relatively large-scale population-based study.

METHODS

Case-control studies and quantitative trait analyses were carried out in 7677 Danish Caucasians who were genotyped for the Arg389Gly variant (dbSNP rs1801253) using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

RESULTS

A weak association between the Gly allele of the Arg389Gly variant and obesity was observed when comparing cases (n = 1540) defined as body mass index (BMI) > 30 kg/m(2) with control subjects (n = 6108) defined as BMI < or = 30 kg/m(2) for both allele frequencies (P = 0.05) and genotype distribution (P = 0.05). Case-control studies (cases n = 2518; control n = 3981) examining the effect on hypertension showed no association with allele frequencies (P = 0.3) or genotype distribution (P = 0.5); however, in the quantitative trait analyses, individuals carrying the Gly allele had slightly but significantly lower diastolic (Arg/Arg = 81.9 mmHg vs. Gly-allele carriers = 81.5 mmHg) and systolic (Arg/Arg = 129.4 mmHg vs. Gly-allele carriers = 128.8 mmHg) blood pressure as well as a lower mean arterial blood pressure.

CONCLUSION

Our results suggest that the Arg389Gly polymorphism does not have any clinically important impact on the pathogenesis of obesity in Danish white subjects. Furthermore, despite the observed minor influence on blood pressure, this variant is most likely not to be a major contributor to the development of hypertension.

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 ADRB3 Trp64Arg variant and obesity in African-American breast cancer cases

OBJECTIVE

To determine if a missense change at codon 64 of ADRB3 (Trp64Arg), a candidate obesity gene, is associated with obesity and levels of subcutaneous or visceral fat in African-American breast cancer cases. Several observational studies have found that women, who are overweight or obese at the time of diagnosis, as well as those who gain weight after diagnosis, are at greater risk for breast cancer recurrence and death than non-overweight women.

DESIGN

Prospective cohort of breast cancer cases.

SUBJECTS

219 African-American breast cancer patients participating in the Los Angeles component of the Health, Eating, Activity and Lifestyle Study.

MEASURES

ADRB3 Trp64Arg genotype, measures of weight including body mass index (BMI), weight gain (weight 5 years before diagnosis compared with weight at 30 months after diagnosis), obesity (BMI> or =30 kg/m(2)), waist/hip circumference and visceral or subcutaneous fat were determined by magnetic resonance imaging.

RESULTS

African-American women who were homozygous for the ADRB3 wild-type allele had significantly higher mean visceral fat levels than women who carried the variant (P=0.04), and were significantly more likely to be obese (odd ratios (OR)=2.1, 95% confidence interval (CI)=1.1-4.2). The association with obesity was most pronounced among women who were premenopausal (OR=4.8, 95% CI=1.3-18), who received chemotherapy for their breast cancer (OR=6.1, 95% CI=1.8-20), or who were not physically active (OR=3.9, 95% CI=1.5-9.7).

CONCLUSION

The wild-type allele of the ADRB3 missense change was associated with measures of obesity in our sample of African-American women. The association was modified by menopausal status, history of chemotherapy and modest levels of physical activity. These results will need to be confirmed in an independent sample.

G-protein beta3 subunit (GNB3) gene polymorphisms and cardiovascular disease: the Ludwigshafen Risk and Cardiovascular Health (LURIC) study

A common 825C>T polymorphism in exon 10 of the gene for the beta-3 subunit of heterotrimeric G-proteins, GNB3, has been associated in some studies with traits of the metabolic syndrome as well as coronary artery disease (CAD), but these associations were refuted by other studies. To investigate the role of GNB3 gene variations in CAD and myocardial infarction (MI), we determined five GNB3 polymorphisms (-1429G>A, IVS5 +41G>A, 657T>A, 814G>A and 825C>T) in the Ludwigshafen Risk and Cardiovascular Health (LURIC) cohort, including 2575 patients with angiographically documented CAD and 731 individuals in whom CAD had been ruled out by angiography. None of the GNB3 polymorphisms was associated with CAD, MI, diabetes, hypertension, blood pressure, body weight or body mass index. We conclude that a major contribution of GNB3 gene variants to CAD or MI risk is unlikely.

Genetic diseases associated with heterotrimeric G proteins

Heterotrimeric G proteins couple receptors for diverse extracellular signals to effector enzymes or ion channels. Each G protein comprises a specific alpha-subunit and a tightly bound betagamma dimer. Several human disorders that result from genetic G-protein abnormalities involve the imprinted GNAS gene, which encodes Gs alpha, the ubiquitously expressed alpha-subunit that couples receptors to adenylyl cyclase and cAMP generation. Loss-of-function and gain-of-function mutations, in addition to imprinting defects, of this gene lead to diverse clinical phenotypes. Mutations of GNAT1 and GNAT2, which encode the retinal G proteins (transducins), are rare causes of specific congenital visual defects. Common polymorphisms of the GNAS and GNB3 (which encodes Gbeta3) genes have been associated with multigenic disorders (e.g. hypertension and metabolic syndrome). To date, no other G proteins have been implicated directly in human disease.