Polymorphisms of the beta2 -adrenoceptor (ADRB2) gene and essential hypertension: the ECTIM and PEGASE studies

Single Nucleotide Polymorphisms in Amlodipine-Associated Genes and Their Correlation with Blood Pressure Control among South African Adults with Hypertension

Objective: This study describes the single nucleotide polymorphisms (SNPs) in amlodipine-associated genes and assesses their correlation with blood pressure control among South African adults with hypertension. Methods: In total, 304 hypertensive patients on amlodipine treatment belonging to the indigenous Swati, Xhosa and Zulu population groups of South Africa were recruited between June 2017 and June 2019. Participants were categorized into: controlled (blood pressure < 140/90 mmHg) and uncontrolled (blood pressure ≥ 140/90 mmHg) hypertension. Thirteen SNPs in amlodipine pharmacogenes with a high PharmGKB evidence base were selected and genotyped using MassArray (Agena BioscienceTM). Logistic regression was fitted to identify significant associations between the SNPs and blood pressure control with amlodipine. Results: The majority of the participants were females (76.6%), older than 45 years (89.1%) and had uncontrolled hypertension (52.3%). Of the 13 SNPs genotyped, five SNPs, rs1042713 (minor allele frequency = 45.9%), rs10494366 (minor allele frequency = 35.3%), rs2239050 (minor allele frequency = 28.7%), rs2246709 (minor allele frequency = 51.6%) and rs4291 (minor allele frequency = 34.4%), were detected among the Xhosa participants, while none were detected among the Swati and Zulu tribal groups. Variants rs1042713 and rs10494366 demonstrated an expression frequency of 97.5% and 79.5%, respectively. Variant TA genotype of rs4291 was significantly associated with uncontrolled hypertension. No association was established between blood pressure response to amlodipine and the remaining four SNPs. Conclusions: This study reports the discovery of five SNPs in amlodipine genes (rs2239050, rs2246709, rs4291, rs1042713 and rs10494366) among the indigenous Xhosa-speaking tribe of South Africa. In addition, the TA genotype of rs4291 was associated with blood pressure control in this cohort. These findings might open doors for more pharmacogenomic studies, which could inform innovations to personalised anti-hypertensive treatment in the ethnically diverse population of South Africa.

Novel candidate genes important for asthma and hypertension comorbidity revealed from associative gene networks

BACKGROUND

Hypertension and bronchial asthma are a major issue for people's health. As of 2014, approximately one billion adults, or ~ 22% of the world population, have had hypertension. As of 2011, 235-330 million people globally have been affected by asthma and approximately 250,000-345,000 people have died each year from the disease. The development of the effective treatment therapies against these diseases is complicated by their comorbidity features. This is often a major problem in diagnosis and their treatment. Hence, in this study the bioinformatical methodology for the analysis of the comorbidity of these two diseases have been developed. As such, the search for candidate genes related to the comorbid conditions of asthma and hypertension can help in elucidating the molecular mechanisms underlying the comorbid condition of these two diseases, and can also be useful for genotyping and identifying new drug targets.

RESULTS

Using ANDSystem, the reconstruction and analysis of gene networks associated with asthma and hypertension was carried out. The gene network of asthma included 755 genes/proteins and 62,603 interactions, while the gene network of hypertension - 713 genes/proteins and 45,479 interactions. Two hundred and five genes/proteins and 9638 interactions were shared between asthma and hypertension. An approach for ranking genes implicated in the comorbid condition of two diseases was proposed. The approach is based on nine criteria for ranking genes by their importance, including standard methods of gene prioritization (Endeavor, ToppGene) as well as original criteria that take into account the characteristics of an associative gene network and the presence of known polymorphisms in the analysed genes. According to the proposed approach, the genes IL10, TLR4, and CAT had the highest priority in the development of comorbidity of these two diseases. Additionally, it was revealed that the list of top genes is enriched with apoptotic genes and genes involved in biological processes related to the functioning of central nervous system.

CONCLUSIONS

The application of methods of reconstruction and analysis of gene networks is a productive tool for studying the molecular mechanisms of comorbid conditions. The method put forth to rank genes by their importance to the comorbid condition of asthma and hypertension was employed that resulted in prediction of 10 genes, playing the key role in the development of the comorbid condition. The results can be utilised to plan experiments for identification of novel candidate genes along with searching for novel pharmacological targets.

Beta2-Adrenergic Receptor Gene Polymorphisms in Egyptian Patients with Acute Myocardial Infarction

Background. Beta2-adrenergic receptor (ADRB2) gene polymorphisms, Arg16Gly and Gln27Glu, have been implicated in the pathogenesis of cardiovascular diseases. The aim of this study was to determine the association of these two polymorphisms with the risk of myocardial infarction (MI) in the Egyptian population. Methods. Blood samples were collected from 68 MI patients and 75 healthy controls. They were assessed for the presence of cardiovascular risk factors and genotyped for the Arg16Gly (rs1042713) and Gln27Glu (rs1042714) polymorphisms using allelic-discrimination polymerase chain reaction. Results. There is no significant difference in genotype and allele frequencies at codon 16 between MI patients and controls (P=0.919). However, at codon 27, MI risk was higher in Gln27 homozygous participants than in Glu27 carriers (P=0.045). The haplotype frequency distribution showed significant difference among cases and controls (P=0.002); homozygotes for Gly16/Gln27 haplotype were more susceptible to MI than Gly16/Glu27 carriers. Patients with Arg16/Gln27 haplotype had higher serum total cholesterol levels (P<0.05) and lower frequency of diabetes in MI patients (P<0.01). However, both Glu27 genotypes and haplotype showed lower frequency of hypertension (P<0.001). Conclusions. Our findings suggested that the ADRB2 gene polymorphisms may play an important role in susceptibility of MI among Egyptian population.

Polymorphic variants of adrenoceptors: pharmacology, physiology, and role in disease

The human genome encodes nine different adrenoceptor genes. These are grouped into three families, namely, the α1-, α2-, and β-adrenoceptors, with three family members each. Adrenoceptors are expressed by most cell types of the human body and are primary targets of the catecholamines epinephrine and norepinephrine that are released from the sympathetic nervous system during its activation. Upon catecholamine binding, adrenoceptors change conformation, couple to and activate G proteins, and thereby initiate various intracellular signaling cascades. As the primary receivers and transducers of sympathetic activation, adrenoceptors have a central role in human physiology and disease and are important targets for widely used drugs. All nine adrenoceptor subtypes display substantial genetic variation, both in their coding sequence as well as in adjacent regions. Despite the fact that some of the adrenoceptor variants range among the most frequently studied genetic variants assessed in pharmacogenetics to date, their functional relevance remains ill defined in many cases. A substantial fraction of the associations reported from early candidate gene approaches have not subsequently been confirmed in different cohorts or in genome-wide association studies, which have increasingly been conducted in recent years. This review aims to provide a comprehensive overview of all adrenoceptor variants that have reproducibly been detected in the larger genome sequencing efforts. We evaluate these variants with respect to the modulation of receptor function and expression and discuss their role in physiology and disease.

Understanding the genetics of coronary artery disease through the lens of noninvasive imaging

Coronary artery disease is a common condition with a known heritable component that has spurred interest in genetic research for decades, resulting in a handful of candidate genes and an appreciation for the complexity of its genetic contributions. Recent advances in sequencing technologies have resulted in large-scale association studies, possibly adding to our current understanding of the genetics of coronary artery disease. Sifting through the statistical noise, however, requires the selection of effective phenotypic markers. New imaging technologies have improved our ability to detect subclinical atherosclerosis in a safe and reproducible manner in large numbers of patients. In this article, we propose that advances in imaging technology have generated improved phenotypic markers for genetic association studies of coronary artery disease.

Association study of the β2-adrenergic receptor gene polymorphisms and hypertension in the Northern Han Chinese

Background

The β2-adrenergic receptor (ADRB2) gene has been widely researched as a candidate gene for essential hypertension (EH), but no consensus has been reached in different ethnicities. The aim of the present study was to evaluate the possible association between the ADRB2 gene polymorphisms and the EH risk in the Northern Han Chinese population.

Methodology/Principal Findings

This study included 747 hypertensive subjects and 390 healthy volunteers as control subjects in the Northern Han Chinese. Genotyping was performed to identify the C-47T, A46G and C79G polymorphisms of the ADRB2 gene. G allelic frequency of A46G polymorphism was significantly higher in hypertensive subjects (P = 0.011, OR = 1.287, 95%CI [1.059–1.565]) than that in controls. Significant association could also be found in dominant genetic model (GG+AG vs. AA, P = 0.006, OR = 1.497, 95%CI [1.121–1.998]), in homozygote comparison (GG vs. AA, P = 0.025, OR = 1.568, 95%CI [1.059–2.322]), and in additive genetic model (GG vs. AG vs. AA, P = 0.012, OR = 1.282, 95%CI [1.056–1.555]). Subgroup analyses performed by gender suggested that this association could be found in male, but not in female. Stratification analyses by obesity showed that A46G polymorphism was related to the prevalence of hypertension in the obese population (GG vs. AG vs. AA, P<0.001, OR = 1.645, 95%CI [1.258–2.151]). Significant interaction was found between A46G genotypes and body mass index on EH risk. No significant association could be found between C-47T or C79G polymorphism and EH risk. Linkage disequilibrium was detected between the C-47T, A46G and C79G polymorphisms. Haplotype analyses observed that the T-47-A46-C79 haplotype was a protective haplotype for EH, while the T-47-G46-C79 haplotype increased the risk.

Conclusions/Significances

We revealed that the ADRB2 A46G polymorphism might increase the risk for EH in the Northern Han Chinese population.

β2 adrenergic receptor polymorphisms and nocturnal blood pressure dipping status in the Wisconsin Sleep Cohort Study

Nondipping nocturnal blood pressure (BP) is associated with target organ damage and cardiovascular disease. We hypothesized that β1- and β2-AR-associated single nucleotide polymorphisms (SNPs) would associate with nondipping BP patterns. Participants (n = 497, age range 30-74 years, 40% female) of the Wisconsin Sleep Cohort Study with at least one ambulatory BP monitoring test were included. Nondipping was defined as less than a 10% dip in sleep BP compared with wake BP. Dipping ratios were calculated as sleep/wake BP. Single nucleotide polymorphisms in the β1-AR (rs7076938, tagging for Gly389Arg) and β2-AR (rs17778257 and rs2400707, tagging for Arg16Gly and Gln27Glu) were selected. β2-AR SNP rs2400707 A-positive subjects (tagging for Glu27) had higher systolic and diastolic dipping ratios in a dose-response fashion. Systolic dipping ratios were: GG = 0.846; AG = 0.854; AA = 0.861 (P = .015). Diastolic dip ratios were: GG = 0.807; AG = 0.815; AA = 0.824 (P = .026). The β2-AR rs17778257/rs2400707 A/A haplotype was associated with dipping ratios and systolic nondipping status (nondipping odds radio 2.0 [1.0-3.8] for A/A versus A/G). Results were similar when models included participants on antihypertensive medications. Higher dipping ratios indicating a lack of nocturnal BP dipping are associated with β2-AR polymorphisms. Nocturnal dipping patterns may be modulated by β2-AR polymorphisms.

Relationships of adrenoceptor polymorphisms with obesity

Obesity, hypertension, and type 2 diabetes are rapidly growing public health problems. Heightened sympathetic nerve activity is a well-established observation in obesity, hypertension, and type 2 diabetes. Human obesity, hypertension, and diabetes have strong genetic as well as environmental determinants. Reduced energy expenditure and resting metabolic rate are predictive of weight gain, and the sympathetic nervous system participates in regulating energy balance through thermogenesis. The thermogenic effects of catecholamines in obesity are mainly mediated via the β2, and β3-adrenergic receptors in humans. Further, β2-adrenoceptors importantly influence vascular reactivity and may regulate blood pressure. β-adrenoceptor polymorphisms have also been associated with adrenoceptor desensitization, increased adiposity, insulin resistance, and enhanced sympathetic nervous activity. Many epidemiological studies have shown strong relationships between adrenoceptor polymorphisms and obesity, but the observations have been discordant. This paper will discuss the current topics involving the influence of the sympathetic nervous system and β2- and β3-adrenoceptor polymorphisms in obesity.

A46G and C79G polymorphisms in the β2-adrenergic receptor gene (ADRB2) and essential hypertension risk: a meta-analysis

No consensus has been reached on the association between the β2-adrenergic receptor polymorphisms A46G and C79G and essential hypertension risk. We performed a meta-analysis to confirm the possible association. After reviewing 303 reports in PubMed and 359 reports in Embase, we included in our meta-analysis 18 articles (20 studies) that met our inclusion criteria. The fixed-effects model and the random-effects model were applied for dichotomous outcomes to combine the results of the individual studies. There was no statistical association between A46G and hypertension risk in all subjects, Asians or Caucasians. However, an association was observed in the dominant genetic model (AA vs. (AG+GG)) (P=0.04, odds ratio (OR)=1.38, 95% confidence interval (CI) 1.01-1.87, P(heterogeneity)=0.98, fixed-effects model) in the subgroup of mixed Africans. No overall statistical association could be found between C79G and hypertension risk or any ethnic subgroup. In the research conducted on severe hypertension (systolic blood pressure ≥160 mm Hg and/or diastolic blood pressure ≥95 mm Hg hypertensive population), significant association was found in the dominant genetic model (CC vs. (CG+GG)) (P=0.04, OR=1.38, 95% CI 1.02-1.86, P(heterogeneity)=0.03, random-effects model), and there was also a borderline significance between the C79 allele and severe hypertension (P=0.05, OR=1.26, 95% CI 1.00-1.57, P(heterogeneity)=0.04, random-effects model). No association could be found in this study between the two polymorphisms and stage 2 hypertension. More studies stratified for different ethnicities and different stages of hypertension should be performed in the future.

Adrenergic signaling polymorphisms and their impact on cardiovascular disease

This review examines the impact of recent discoveries defining personal genetics of adrenergic signaling polymorphisms on scientific discovery and medical practice related to cardiovascular diseases. The adrenergic system is the major regulator of minute-by-minute cardiovascular function. Inhibition of adrenergic signaling with pharmacological beta-adrenergic receptor antagonists (beta-blockers) is first-line therapy for heart failure and hypertension. Advances in pharmacology, molecular biology, and genetics of adrenergic signaling pathways have brought us to the point where personal genetic differences in adrenergic signaling factors are being assessed as determinants of risk or progression of cardiovascular disease. For a few polymorphisms, functional data generated in cell-based systems, genetic mouse models, and pharmacological provocation of human subjects are concordant with population studies that suggest altered risk of cardiovascular disease or therapeutic response to beta-blockers. For the majority of adrenergic pathway polymorphisms however, published data conflict, and the clinical relevance of individual genotyping remains uncertain. Here, the current state of laboratory and clinical evidence that adrenergic pathway polymorphisms can affect cardiovascular pathophysiology is comprehensively reviewed and compared, with a goal of placing these data in the broad context of potential clinical applicability.

Haplotypes of the adrenergic system predict the blood pressure response to beta-blockers in women with essential hypertension

AIMS

To analyze the association of haplotypes of the adrenergic system with essential hypertension and with the blood pressure response to beta-blockers.

MATERIALS & METHODS

In 1112 never-treated essential hypertension patients and 203 normotensive controls, tightly linked SNPs of beta-adrenergic receptors (ADRB1 - Ser49Gly and Arg389Gly; ADRB2 - Cys19Arg, Gly16Arg and Gln27Glu) and the G-protein beta3-subunit (GNB3 - A3882C, G5249A and C825T) were genotyped. Association of haplotypes with essential hypertension and with the blood pressure response to atenolol 50 mg twice daily in a subgroup of essential hypertension patients (n = 340) was evaluated (Haploview 3.2).

RESULTS

No SNPs or haplotypes were associated with essential hypertension. In females only, GNB3 SNPs and haplotypes were associated with the blood pressure response (p < 0.05).

CONCLUSION

Our study confirmed the sex-specific association of GNB3 with the blood pressure response to atenolol with no substantial advantage of the analysis of haplotypes over SNPs.

Polymorphisms in the ACE and ADRB2 genes and risks of aging-associated phenotypes: the case of myocardial infarction

Multiple functions of the beta2-adrenergic receptor (ADRB2) and angiotensin-converting enzyme (ACE) genes warrant studies of their associations with aging-related phenotypes. We focus on multimarker analyses and analyses of the effects of compound genotypes of two polymorphisms in the ADRB2 gene, rs1042713 and rs1042714, and 11 polymorphisms of the ACE gene, on the risk of such an aging-associated phenotype as myocardial infarction (MI). We used the data from a genotyped sample of the Framingham Heart Study Offspring (FHSO) cohort (n = 1500) followed for about 36 years with six examinations. The ADRB2 rs1042714 (C-->G) polymorphism and two moderately correlated (r(2) = 0.77) ACE polymorphisms, rs4363 (A-->G) and rs12449782 (A-->G), were significantly associated with risks of MI in this aging cohort in multimarker models. Predominantly linked ACE genotypes exhibited opposite effects on MI risks, e.g., the AA (rs12449782) genotype had a detrimental effect, whereas the predominantly linked AA (rs4363) genotype exhibited a protective effect. This trade-off occurs as a result of the opposite effects of rare compound genotypes of the ACE polymorphisms with a single dose of the AG heterozygote. This genetic trade-off is further augmented by the selective modulating effect of the rs1042714 ADRB2 polymorphism. The associations were not altered by adjustment for common MI risk factors. The results suggest that effects of single specific genetic variants of the ADRB2 and ACE genes on MI can be readily altered by gene-gene or/and gene-environmental interactions, especially in large heterogeneous samples. Multimarker genetic analyses should benefit studies of complex aging-associated phenotypes.

Polymorphisms in α- and β-Adrenergic Receptor Genes, Hypertension, and Obstructive Sleep Apnea: The Skaraborg Sleep Study

The sympathetic nervous system and the adrenergic receptors play an important role in regulation of blood pressure. This study explored the associations between functional polymorphisms of the α(2B)-, β(1)-, and β(2)-adrenergic receptor genes and obstructive sleep apnea (OSA) in hypertensive patients and hypertension in patients with OSA in a populationbased sample of 157 hypertensive patients and 181 healthy control subjects. Only the Arg389Gly polymorphism of the β(1)-adrenergic receptor gene was associated with increased risk for mild OSA in hypertensive patients (Arg/Arg versus Gly/Arg/Gly/Gly, 2.1, 95% CI, 1.02-4.7). Hypertensive men carrying the Arg389Arg genotype had higher crude and age-adjusted AHI than carriers of the Arg389Gly/Gly389Gly genotypes. When adjusted also for BMI this difference became borderline significant. This difference was not observed in women. The risk of hypertension in mild OSA was associated with increasing number of Arg-alleles (Arg/Arg OR 5.4, 95% CI 1.4-21.2).

Synopsis and data synthesis of genetic association studies in hypertension for the adrenergic receptor family genes: the CUMAGAS-HYPERT database

BACKGROUND

The adrenergic receptor (adrenoceptor) family genes have been extensively studied as candidate genes in hypertension but the results of individual genetic association studies (GAS) are controversial and inconclusive. To clarify these data, a systematic assessment of GAS for adrenoceptor family genes in hypertension was conducted.

METHODS

Data from 163 GAS involving 7 genes and 37 distinct genetic variants were analyzed and cataloged in CUMAGAS-HYPERT (Cumulative Meta-analysis of Genetic Association Studies-HYPERTension; a web-based information system, which allows the retrieval and synthesis of data from GAS in hypertension, available at http://biomath.med.uth.gr). Data from genome-wide association studies involving the adrenoceptor family genes were also systematically searched.

RESULTS

Individual GAS reported inconsistent associations and had limited power to detect modest genetic effects, with only 1.2% having power >80%. Thirteen variants were investigated by three or more studies and their results were subject to meta-analysis. In the main meta-analyses, significant results were shown for five variants (ADRB1 p.Arg389Gly, ADRB1 p.Ser49Gly, ADRB2 g.9368308A>G, ADRB3 p.Trp64Arg, and ADRA1A p.Cys347Arg) under the allelic contrast and/or the dominant model. Subgroup analyses by ethnicity and gender detected significant associations for three variants (ADRB1 p.Arg389Gly in east Asians, ADRB2 p.Gln27Glu in whites, and ADRB3 p.Trp64Arg in whites and in males). Heterogeneity ranged from none to high. No significant associations were recorded from genome-wide studies.

CONCLUSIONS

There is evidence to implicate adrenoceptor genes in hypertension, although future studies designed to investigate epistatic and gene-environment interactions would allow more solid conclusions to be drawn about the role of these genes in hypertension.

Non-synonymous single-nucleotide polymorphisms associated with blood pressure and hypertension

In this study, we determined the association of 1180 non-synonymous single-nucleotide polymorphisms (SNPs) with systolic blood pressure (SBP) and hypertensive status. A total of 8842 subjects were taken from two community-based cohorts--Ansung (n=4183) and Ansan (n=4659), South Korea--which had been established for genome-wide association studies (GWAS). Five SNPs (rs16835244, rs2286672, rs6265, rs17237198 and rs7312017) were significantly associated (P-values: 0.003-0.0001, not corrected for genome-wide significance) with SBP in both cohorts. Of these SNPs, rs16835244 and rs2286672 correlated with risk for hypertension. The rs16835244 SNP replaces Ala288 in arginine decarboxylase (ADC) with serine, and rs2286672 replaces Arg172 in phospholipase D2 (PLD2) with cysteine. A comparison of peptide sequences between vertebrate homologues revealed that the SNPs identified occur at conserved amino-acid residues. In silico analysis of the protein structure showed that the substitution of a polar residue, serine, for a non-polar alanine at amino-acid residue 288 affects a conformational change in ADC, and that Arg172 in PLD2 resides in the PX domain, which is important for membrane trafficking. These results provide insights into the function of these non-synonymous SNPs in the development of hypertension. The study investigating non-synonymous SNPs from GWAS not only by statistical association analysis but also by biological relevance through the protein structure might be a good approach for identifying genetic risk factors for hypertension, in addition to discovering causative variations.

Association of beta-1 and beta-2 adrenergic receptor gene polymorphisms with myocardial infarction

Both beta(1)- and beta2-adrenergic receptors (beta(1)- and beta(2)-AR) have important roles in heart function mainly in response to catecholamines. Some specific polymorphisms in the beta(1)- and beta(2)-AR genes, named ADRB1 and ADRB2, respectively, have been implicated in several cardiovascular and noncardiovascular phenotypes. In this study, we aimed to investigate the possible relationship between Ser49Gly and Arg389Gly polymorphisms of the ADRB1 and Arg16Gly and Gln27Glu polymorphisms of the ADRB2 gene with ST elevation myocardial infarction (MI) in a Turkish population. One hundred patients with ST elevation MI and 100 healthy control subjects were genotyped using the PCR-RFLP method. Although the Arg389 allele of the ADRB1 gene was associated with an elevated risk of MI, the Glu27 allele of the ADRB2 gene was associated with a decreased risk of MI. Carriers of the ADRB1 Arg389 allele (heterozygotes+homozygotes) had an approximately 3.5-fold increased risk for MI than Gly389 homozygotes (OR=3.59, 95% CI=0.96-13.47, P=0.045). For the ADRB2 Gln27Glu polymorphism, subjects having one or two copies of the Glu27 allele showed a decreased risk of MI compared with Gln27 homozygote subjects (OR=0.48, 95% CI=0.24-0.94, P=0.03). Haplotype analysis of these polymorphisms showed no significant differences between groups. These results suggest that the Arg389Gly and Gln27Glu polymorphisms may be associated with an altered risk of MI in this Turkish population.

GENETIC VARIATION IN THE β(2)-ADRENERGIC RECEPTOR: IMPACT ON INTERMEDIATE CARDIOVASCULAR PHENOTYPES

Genetic variation in drug targets (e.g. receptors) can have pronounced effects on clinical responses to endogenous and exogenous agonists. Polymorphisms in the gene encoding the β(2)-adrenergic receptor (β(2)-AR) have been associated with altered expression, down-regulation, and altered cell signaling in vitro. Because β(2)-ARs play a crucial role in the regulation of the cardiovascular system, the functional importance of genetic variation in the β(2)-AR on cardiovascular responses to physiological or pharmacological stimuli has gained widespread attention. The objective of this review is to characterize these intermediate cardiovascular phenotypes and their influence on cardiovascular disease and adrenergic drug responses.Two common single nucleotide polymorphisms, encoded at codon 46 (Gly(16)Arg) and 79 (Gln(27)Glu) of the β(2)-AR gene, have been studied intensively. They have been shown to be associated with altered vasodilator responses to regional and systemic administration of β(2)-agonists, altered cardiovascular responses to sympathoexcitatory maneuvers, and altered myocardial function. Importantly, these intermediate physiological patterns may influence the development of and the outcomes associated with hypertension and other cardiovascular diseases. As recently reported, β(2)-AR gene variation can risk-stratify patients receiving β-blocker therapy and may predict β-blocker efficacy in patients post acute coronary syndrome or in patients with heart failure.Further studies will advance our understanding of the link between β(2)-AR genotypes, intermediate cardiovascular phenotypes, and clinical phenotypes. In the long term, reassessment of the benefits of β-blocker-therapy within genotype groups should be carried out with the ultimate goal to design the optimal therapeutic regimen for the individual patient.

beta1- and beta2-adrenergic receptor gene variation, beta-blocker use and risk of myocardial infarction and stroke

BACKGROUND

The benefits of beta-blocker therapy may depend on underlying genetic susceptibility.

METHODS

We investigated the interaction of common variation in beta1 and beta2 adrenergic receptor (AR) genes with beta-blocker use on the risks of myocardial infarction (MI) and ischemic stroke in a case-control study. Participants were treated pharmacologically for hypertension, aged 30-79 years, with incident MI (n = 659) or ischemic stroke (n = 279) between 1995 and 2004, and 2,249 matched controls.

RESULTS

We observed an interaction of beta-blocker use with beta1-AR gene variation on MI risk (P value, 6 degrees of freedom: 0.01) and ischemic stroke risk (P value, 6 degrees of freedom: 0.04). Compared with use of other antihypertensive medications, beta-blocker use was associated with higher MI risk in carriers of one or two copies of rs#17875422 (Odds ratio (OR): 2.66, 95% confidence interval (CI); 1.26-5.60) but not in homozygous carriers of the common allele (OR: 0.88, 95% CI: 0.73-1.07). Another variant, rs#2429511, interacted with beta-blocker use on both MI and ischemic stroke risks. beta-blocker use was associated with higher risk of combined MI and ischemic stroke in carriers of rs#2429511 (OR: 1.24, 95% CI: 1.03-1.50) but not in homozygous carriers of common allele (OR: 0.70, 95% CI: 0.51-0.94). beta-blocker use did not interact with beta2-AR gene variation on the risks of MI and ischemic stroke.

CONCLUSIONS

These results, which require replication, suggest genetic variants in the beta1-AR gene may determine whether to use beta-blockers in hypertension for the primary prevention of cardiovascular disease.

GLU-27 variant of β2-adrenergic receptor polymorphisms is an independent risk factor for coronary atherosclerotic disease

OBJECTIVE

Arg16Gly and Gln27Glu polymorphism of beta(2)-adrenergic receptors (beta 2AR) have been associated with several risk factors for coronary atherosclerotic disease (CAD). Nevertheless, conflicting data have been reported concerning their influence on CAD and cardiovascular clinical events.

AIM

To investigate whether (a) beta 2AR polymorphisms are associated with CAD; and (b) the potential impact, if any, of these polymorphisms on cardiovascular clinical events in patients presenting with angina-like pain or silent ischemia.

METHODS AND RESULTS

We screened 786 consecutive patients referred to cardiac catheterization because of angina-like pain or silent ischemia for Arg16Gly, Gln27Glu, Thr164Ile beta 2AR polymorphisms. Patients were divided in 2 groups according to the presence or absence of CAD at the angiography. Hundred subjects from blood donor center served as controls. Clinical endpoints were evaluated at baseline and up to 6 years follow-up. Glu-27 homozygous genotype and Glu-27 allele (Glu-27, allele frequency: 47% CAD versus 39% NO CAD, p<0.05) were more frequent in patients with CAD. At multivariate analysis, patients carrying Glu-27 allele showed a significantly higher risk of developing CAD (OR: 1.78, 95% CI: 1.21-2.63, p=0.004). At clinical follow-up, a higher incidence of coronary revascularization was noted in Glu-27 homozygotes as compared with Gln-27 homozygote patients.

CONCLUSIONS

In patients at high risk for CAD and/or angina-like pain, Glu-27 allele of beta2 adrenergic receptor polymorphism is an independent risk factor for CAD and appears to be associated with higher incidence of myocardial revascularization.

A review of the genetics of essential hypertension

PURPOSE OF REVIEW

Essential hypertension affects more than 20% of the adult population, and has a multifactorial origin arising from an interaction between susceptibility genes and environmental factors. Several strategies have been used to identify hypertension susceptibility genes. This review highlights recent efforts in genetic dissection of essential hypertension.

RECENT FINDINGS

Recently, further chromosomal regions harboring blood pressure loci have emerged in genome-wide linkage studies. Findings from a new systematic two-dimensional genome scan are presented, as well as sex-specific loci linked to hypertension in inbred rodent models. Many case-control association studies have been carried out, but results so far have been equivocal. This review discusses some interesting studies combining linkage and association strategies using gene-gene interactions, and studies the use of haplotypes instead of SNPs. Two novel hypertension susceptibility genes are presented, and a short summary on new insights into genes of the renin-angiotensin and adrenergic systems is given.

SUMMARY

To date, linkage and association studies have not been convincing. Genome-wide association studies may prove to be an effective approach to the problems posed by complex traits. Combined with candidate gene approaches, it is hoped this strategy will yield convincing evidence for genes associated with essential hypertension.

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.

A simple method for the identification of three major haplotypes of the β2AR

We have developed a simple and efficient SSCP (single strand conformational polymorphism) method for haplotype determination of beta2AR using four polymorphisms. The six different SSCP patterns were grouped into three major haplotypes named I, II and III. We studied a population of 199 individuals displaying all the haplotypes: 34.9% (group I), 36.1% (group II) and 29.5% (group III). This population was subdivided into three groups: normal weight, overweight and obese individuals. There were no significant differences between the haplotypes of normal and overweight individuals. The haplotype frequencies in the group of normal weight subjects were 39% (I), 33% (II) and 28% (III). The overweight individuals presented frequencies of 38% (I), 33% (II) and 29% (III). The obese group showed marked differences for haplotypes I and II: 27.1% (I), 43.2% (II) and 29.7% (III) when compared to the normal weight group. For haplotype I the p value of normal to obese groups was 0.0403 with an odds ratio of 0.5761. Our two step SSCP method for beta2AR haplotyping is simple, accurate and cost effective for studying large populations and may be a useful tool for easy and accurate identification of haplotype I which appears to have a protective role against developing obesity.

Genetics of stress response and stress-related disorders

The major findings regarding the genetics of stress response and stress-related disorders are: (i) variations in genes involved in the sympathetic system or in the hypothalamic-pituitary-adrenocortical axis are associated with altered stress responses; (ii) genes related to the renin-angiotensin-aldosterone system or inflammation/immune response show associations with cardiovascular disorders; (iii) genes involved in monoaminergic neurotransmitter systems are associated with bipolar disorder and unipolar depression. The vast majority of these association studies followed a conventional hypothesis-driven approach, restricting the gene selection to established candidates. This very conservative approach retarded our understanding of the complex interplay between genetic factors, stress response, and stress-related disorders. Chip-based whole-genome technologies will open up access to new unbiased and statistically efficient approaches that will help to identify new candidate genes, which should be thoroughly validated in clinical and preclinical confirmatory studies. This, together with the use of new text- and information-mining tools, will bring us closer to integrating all the findings into sophisticated models delineating the pathways from genes to stress response and stress-related disorders.

The Emerging Pharmacogenomics of the β‐Adrenergic Receptors

Beta-adrenergic signaling mechanisms are of central importance to cardiovascular health and disease. Modulation of these pathways represents an important pharmacologic approach to the treatment of heart failure and hypertension. Advances in molecular genetics have identified genetic polymorphisms in the human beta-adrenergic receptor genes; some of this variation predicts changes in protein sequence/structure, and potentially changes in function, of the b-adrenergic receptors. This article reviews the current state of knowledge and understanding of the genetic variation present in the three human beta-adrenergic receptor genes. Already, variation in these genes has been associated with observed differences in several cardiovascular phenotypes. This work has led to the demonstration of functional differences in activity between receptors with certain known polymorphisms and "wild-type" receptors. An understanding of these polymorphisms is key to the development of studies of how differences in drug response/effects may be mediated by these polymorphisms. Such studies are anticipated to provide a foundation for the development of novel pharmacologic approaches where selection of and dosing of cardiovascular therapy is tailored to individuals on the basis of each patient's specific genetic makeup.

Genetics of arterial hypertension and hypotension

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

Polymorphisme génétique des récepteurs bêta-adrénergiques et mortalité dans l’ischémie myocardique

The genetic polymorphism of beta-2 adrenergic receptors (B2AR) could play a major role in the prognostic of patients with a coronary heart disease. Two recent epidemiological studies could support this hypothesis. In 597 patients treated by a beta-blocker and followed for 3 years after a myocardial infarction or an acute coronary syndrome, the death rate was 5.4 times higher in homozygous Arg 16 and Gln 27 B2AR genotypes than in heterozygous or homozygous Gly 16 and Glu 27 B2AR genotypes. The beta-1 adrenergic receptor (B1AR) genetic polymorphism did not modify mortality. In a second study, in a prospective cohort of 5249 patients aged > or =65 years, the incidence of sudden cardiac death was 1.56 times higher in patients with homozygous Gln 27 B2AR than in heterozygous or homozygous Glu 27 B2AR genotype. This result was confirmed by a case-control study (155 cases of sudden cardiac death versus 144 control subjects). These data suggest that B2AR genetic polymorphism should be systematically studied in clinical trials in myocardial ischemia, with or without congestive heart failure.

Dietary sodium restriction and beta2-adrenergic receptor polymorphism modulate cardiovascular function in humans

Dietary Na+ intake influences beta2-adrenergic receptor (beta2AR) responsiveness. While receiving a normal Na+ diet (150 mmol day(-1)), subjects homozygous for glycine at amino acid 16 (Gly16) have greater forearm beta2AR-mediated vasodilatation than subjects homozygous for arginine (Arg16), an effect that is mediated by endothelial NO. We tested the hypothesis that dietary Na+ restriction eliminates genotype differences in forearm and systemic beta2AR-mediated dilatation in these groups. We measured heart rate, mean arterial pressure and cardiac output (CO, acetylene breathing) responses to administration of intravenous terbutaline (TRB) before and after 5 days of low dietary Na+ intake (10 mmol day(-1)) in healthy Gly16 (n = 17; age, 31 +/- 7 year) and Arg16 homozygotes (n = 15; age, 29 +/- 8 year). After the low-Na+ diet, a catheter was placed in the brachial artery to measure forearm blood flow (FBF, plethysmography) responses to administration of isoprenaline (isoproterenol) before and after NO inhibition with NG-mono-methyl-L-arginine (L-NMMA). In the Gly16 group, the low-Na+ diet decreased baseline CO from 6.4 +/- 1.4 to 5.5 +/- 1.2 l min(-1) (P = 0.003, paired t test), tended to decrease stroke volume from 97.0 +/- 20.6 to 86.9 +/- 21.7 ml (P = 0.06) and increased peripheral resistance from 1106 +/- 246 to 1246 +/- 222 dynes s cm(-5) (P = 0.02); significant effects of the low-Na+ diet were not observed in Arg16 subjects. In a repeated measures ANOVA, the responses of all cardiovascular measures to systemic administration of TRB were not influenced by genotype or diet. Additionally, the FBF response to incremental doses of isoprenaline did not differ between genotype groups before or after administration of L-NMMA. We conclude that dietary Na+ restriction blunted the increased forearm NO-mediated beta2AR responsiveness in Gly16 homozygotes observed in a previous study after normal dietary Na+ intake, while baseline CO decreased and peripheral resistance increased in this group. This study provides evidence that dietary Na+ modulates effects of the Arg16Gly polymorphism on cardiovascular function.

The Arg16Gly polymorphism of the beta2-adrenergic receptor and the natriuretic response to rapid saline infusion in humans

The beta2-adrenergic receptors (beta2ARs) play a role in renal Na+ regulation. Subjects homozygous for glycine at amino acid 16 (Gly16) of the beta2AR have been shown to have enhanced beta2-mediated vascular relaxation when compared to subjects homozygous for arginine (Arg16). However, Gly16 subjects have been shown to have higher blood pressure than Arg16 subjects. Given the dominant role of the kidneys in long-term blood pressure regulation, we sought to determine whether there were differences in renal Na+ handling between Gly16 (n = 17) and Arg16 (n = 14) subjects (Gly16: age, 30 +/- 2 years; body mass index (BMI), 25 +/- 11 kg m(-2); Arg16: age, 30 +/- 2 years; BMI, 25 +/- 1 kg m(-2)). We measured urinary Na+ content before and for 3 h following rapid intravenous saline infusion (30 ml kg(-1) in approximately 16 min). Prior to the infusion, there were no differences in 24-h Na+ excretion between Gly16 and Arg16 subjects (Gly16, 183 +/- 21 mmol; Arg16, 184 +/- 20 mmol); however, systolic blood pressure (SBP) was significantly higher in Gly16 than Arg16 subjects with no differences observed in diastolic blood pressure (DBP) or mean arterial pressure (MAP) (SBP: Gly16, 117 +/- 3 mmHg; Arg16, 109 +/- 2 mmHg; DBP: Gly16, 78 +/- 2 mmHg; Arg16, 77 +/- 2 mmHg; MAP: Gly16, 90 +/- 2 mmHg; Arg16, 89 +/- 2 mmHg). With rapid saline infusion, MAP increased in both genotype groups (Gly16, 6.7%; Arg16, 3.4%; P > 0.05). In the 3 h following Na+ infusion, Na+ excretion was less in Gly16 when compared to Arg16 subjects, with a trend towards significance when expressed as total Na+ excreted (Gly16, 66 +/- 7 mmol; Arg16, 85 +/- 9 mmol; P = 0.07), and a significant difference when expressed as a fraction of the administered load (Gly16, 0.18 +/- 0.02; Arg16, 0.28 +/- 0.03; P < 0.01). These results suggest that the Arg16Gly polymorphism of the beta2AR is associated with differences in natriuretic response to rapid saline infusion, which may influence long-term regulation of blood pressure.

Beta2-adrenergic receptor genetic variants and risk of sudden cardiac death

BACKGROUND

Sympathetic activation influences the risk of ventricular arrhythmias and sudden cardiac death (SCD), mediated in part by the beta2-adrenergic receptor (B2AR). We investigated whether variation in the B2AR gene is associated with SCD risk.

METHODS AND RESULTS

In this study, 4441 white and 808 black Cardiovascular Health Study (CHS) participants were followed up prospectively for SCD and genotyped for B2AR Gly16Arg and Gln27Glu polymorphisms. The study was replicated in 155 case and 144 control white subjects in a population-based case-control study of SCD, the Cardiac Arrest Blood Study (CABS). In CHS, Gly16 and Gln27 allele frequencies were 62.4% and 57.1% among white and 50.1% and 81.4% among black participants. Over a median follow-up of 11.1 years, 156 and 39 SCD events occurred in white and black participants, respectively. The Gln27Glu variant was associated with SCD risk (P=0.008 for general model). SCD risk was higher in Gln27 homozygous participants than in Glu27 carriers (ethnicity-adjusted hazard ratio [HR], 1.56; 95% confidence interval [CI], 1.17 to 2.09; P=0.003). The increased risk did not differ significantly between white (HR, 1.62; 95% CI, 1.18 to 2.23) and black (HR, 1.23; 95% CI, 0.61 to 2.48) participants, although the confidence interval was wide in blacks. In the CABS replication study, Gln27 homozygous participants similarly had higher SCD risk than Glu27 carriers (odds ratio, 1.64; 95% CI, 1.02 to 2.63; P=0.040). Gly16Arg was not associated with SCD risk in either study.

CONCLUSIONS

Gln27 homozygous individuals have an increased risk of SCD in 2 study populations. Our findings suggest that B2AR plays a role in SCD in humans. Study of genetic variation within the B2AR gene may help identify those at increased SCD risk.

Pharmacogenetics of the human beta-adrenergic receptors

The beta-adrenergic receptors (ADRBs) are cell surface receptors that play central roles in the sympathetic nervous system. Pharmacological targeting of two of these receptors, ADRB1 and ADRB2, represents a widely used therapeutic approach for common and important diseases including asthma, hypertension and heart failure. Genetic variation in both ADRB1 and ADRB2 has been linked to both in vitro and clinical disease phenotypes. More recently, interest has shifted to studies that explore potential interaction between variation in ADRBs and medications directed at these important receptors. This paper reviews the current state of knowledge and understanding of ADRB genetic variation and explores the likely direction of future studies in this area.

Haplotypes of the beta-2 adrenergic receptor associate with high diastolic blood pressure in the Caerphilly prospective study

OBJECTIVES

Current evidence demonstrates that both genetic and environmental factors influence blood pressure. The sympathetic nervous system is a key player in blood pressure control and functional genetic variants of the beta-2 adrenergic receptor (B2AR) have been identified and implicated in the pathogenesis of hypertension. The present study aimed to determine the effects of common haplotypes of the B2AR gene upon blood pressure in the Caerphilly Prospective Study.

DESIGN

Two thousand five hundred and twelve men (aged 45-59 years) participated in the study. We selected individuals in the upper (n = 347) and lower (n = 279) quintiles of the diastolic blood pressure distribution fixed at two time points [phase 2 (1984-88) or phase 3 (1989-93)] as cases and controls.

METHODS

We analysed two functional polymorphisms (Arg16Gly and Gln27Glu) of B2AR and their haplotypes.

RESULTS

We found a higher risk of hypertension in individuals homozygous for the Gln27 compared to those individuals homozygous for Glu27 [odds ratio (OR) = 1.94; 95% confidence interval (CI) = 1.34-2.81; P = 0.001]. Three haplotypes (Gly16Gln27, Gly16Glu27 and Arg16Gln27) were present in both quintile groups. Logistic regression analysis showed that haplotypes with a Gln27 allele (Gly16Gln27 and Arg16Gln27) conferred a significantly higher risk for hypertension than the Gly16Glu27 haplotype (OR = 1.55; 95% CI = 1.11-2.17, OR = 1.37; 95% CI = 1.04-1.81; P = 0.009 and P = 0.027, respectively). However, there was no evidence to support a statistically significant difference in odds ratios for the Gly16Gln27 and Arg16Gln27 haplotypes (P = 0.477), suggesting that it is the Gln27 allele alone, rather than any haplotype, which best explains the association.

CONCLUSIONS

In a prospectively studied Caucasian male cohort, high diastolic blood pressure was associated with B2AR haplotypes containing the pro-downregulatory Gln27 variant.

Arg16Gly polymorphism of the beta2-adrenergic receptor is associated with differences in cardiovascular function at rest and during exercise in humans

In humans, subjects homozygous for arginine (ArgArg) at codon 16 of the beta2-adrenergic receptor (beta2AR) have been shown to have greater agonist-mediated desensitization than subjects homozygous for glycine (GlyGly). We sought to determine if this substitution differentially influenced cardiovascular function during short duration (9 min) low and high intensity exercise (40 and 75% of peak work). Healthy Caucasian ArgArg (n = 16), GlyGly (n = 31) and ArgGly (n = 17) subjects matched for age, sex and peak oxygen uptake were studied. There were no differences in adrenaline (ADR) at rest or with heavy exercise, but the ArgArg group had lower ADR with light exercise (P = 0.04). Resting heart rate (HR) was higher in ArgArg (P < 0.01), while cardiac output (Q), stroke volume (SV), and mean arterial pressure (MAP) were lower than the other groups (HR = 86+/-2, 78+/-2, 80+/-1 beats min(-1); Q = 5.7+/-0.81, 6.1+/-0.18, 6.7+/-0.22 l min(-1); SV = 68+/-3, 82+/-3, 89+/-4 ml beat(-1); MAP = 92+/-1, 103+/-2, 98+/-1 mmHg-- for ArgArg, ArgGly and GlyGly, respectively, means +/-s.e.m., P < 0.01), however, no differences were observed in systemic vascular resistance (SVR). With low intensity exercise and high intensity exercise the ArgArg group continued to have a lower , SV and MAP compared to the other groups (P < 0.05), with no differences observed in SVR. During recovery, the ArgArg subjects continued to have a lower MAP but there were no differences in HR, , or SVR. These data suggest that subjects homozygous for Arg at codon 16 of the beta2AR have reduced and MAP at rest that persist during exercise with no evidence for differential changes over the course of exercise despite large changes in catecholamines. This may suggest possible genotype-related differences in baseline receptor function or density which causes phenotypic differences at rest that are sustained during short-term exercise.

Genetic determinants of blood pressure regulation

Hypertension is a multifactorial disorder that probably results from the inheritance of a number of susceptibility genes and involves multiple environmental determinants. Existing evidence suggests that the genetic contribution to blood pressure variation is about 30-50%. Although a number of candidate genes have been studied in different ethnic populations, results from genetic analysis are still inconsistent and specific causes of hypertension remain unclear. Furthermore, the abundance of data in the literature makes it difficult to piece together the puzzle of hypertension and to define candidate genes involved in the dynamic of blood pressure regulation. In this review, we attempt to highlight the genetic basis of hypertension pathogenesis, focusing on the most important existing genetic variations of candidate genes and their potential role in the development of this disease. Our objective is to review current knowledge and discuss limitations to clinical applications of genotypic information in the diagnosis, evaluation and treatment of hypertension. Finally, some principles of pharmacogenomics are presented here along with future perspectives of hypertension.

164Ile allele in the beta2-Adrenergic receptor gene is associated with risk of elevated blood pressure in women. The Copenhagen City Heart Study

OBJECTIVE

Since beta2-adrenergic receptors are important regulators of blood pressure, genetic variation in this receptor could explain risk of elevated blood pressure in selected individuals. We tested the hypothesis that Gly16Arg, Gln27Glu, and Thr164Ile in the beta2-adrenergic receptor gene associated with elevated blood pressure.

METHODS

We genotyped 9185 individuals from the adult Danish general population.

RESULTS

Allele frequencies of 16Arg, 27Glu, and 164Ile were 0.38, 0.44, and 0.01, respectively. Among women never treated with antihypertensive medication those heterozygous for Thr164Ile versus non-carriers had increased diastolic blood pressure (P=0.02). Women heterozygous for Thr164Ile versus non-carriers had an odds ratio for elevated blood pressure of 1.93 (95% CI: 1.30-2.86). Finally, women double heterozygous for Thr164Ile and Gln27Glu or Gly16Arg versus non-carriers at all 3 loci had an odds ratio for elevated blood pressure of 2.49 (1.28-4.85) or 3.19 (1.46-6.97). In men, blood pressure was not influenced by this genetic variation.

CONCLUSION

In women Thr164Ile heterozygosity is associated with increased diastolic blood pressure, and represent a risk factor for elevated blood pressure in women in the general population. This was most pronounced in those women also heterozygous for Gln27Glu or Gly16Arg.

Interactive effects of common beta2-adrenoceptor haplotypes and age on susceptibility to hypertension and receptor function

Few studies have examined to what extent genetic variants of the beta2-adrenoceptor (ADRB2) are involved in the development of hypertension with age, although beta2-adrenergic receptor responsiveness declines in older subjects. To investigate this, 10 common single-nucleotide polymorphisms (SNPs) in the promoter and coding regions of the ADRB2 gene were genotyped in an unrelated population consisting of 2 ethnic groups: European American (EA; n=610) and African American (AA; n=420). ADRB2 haplotypes were estimated by expectation maximization (EM) algorithm-based methods. In the general population for EAs and AAs, the variants of the ADRB2 gene, including the individual SNPs and their haplotypes, were not associated with hypertension. However, there was a significant interaction between age and one of the common haplotypes (haplotype 1) in EAs (P=0.01). Haplotype 1 was associated with protection against hypertension in young (< or =50 years of age) but not in old (>50 years of age) EAs (odds ratio, 0.5; 95% confidence interval, 0.27 to 0.91; P=0.02). This age-specific effect was further supported by the observations that young subjects carrying > or =1 copy of haplotype 1 had significantly lower diastolic blood pressure and nearly 2-fold higher ADRB2 binding density than the noncarriers (P<0.05). With aging, their ADRB2 numbers decreased to the level of the noncarriers, along with increased body mass index (7%; P<0.05) and decreased heart rate (7%; P<0.001). Our study suggests that age is an important modifier for the effects of ADRB2 polymorphisms on ADRB2 function and the development of hypertension.

Genetics of human hypertension

Hypertension is a complex genetic disorder caused by interplay between several "risk" genes and environmental factors (genetic heritability approximately 30%). Most genetic studies of hypertension use a candidate gene approach and two conclusions have been made: there is no association or linkage with the genes studied, or the hypertension phenotype is heterogeneous and subgroups with hypertension related to certain polymorphisms cannot be identified because of background noise. Studies using intermediate phenotypes suggest the latter is most likely. Another problem is the reliability of gene structure assessment: usually only one or two gene polymorphisms are assessed. The use of intermediate phenotypes and dense mapping of candidate genes would provide a better approach for identifying genotype-phenotype correlations, which might enable the use of genotypes to identify more-specific therapeutic and preventative measures for hypertensives.

Hypertension genes are genetic markers for insulin sensitivity and resistance

Insulin resistance is a determinant of blood pressure variation and risk factor for hypertension. Because insulin resistance and blood pressure cosegregate in Mexican American families, we thus investigated the association between variations in 9 previously reported hypertension genes (ACE, AGT, AGTRI, ADDI, NPPA, ADDRB2, SCNN1A, GNB3, and NOS3) and insulin resistance. Families were ascertained via a coronary artery disease proband in the Mexican American Coronary Artery Disease Project. Individuals from 100 Mexican American families (n=656) were genotyped for 14 polymorphisms in the 9 genes and all adult offspring and offspring spouses were phenotyped for insulin sensitivity by hyperinsulinemic euglycemic clamp (n=449). AGT M235T and NOS3 A(-922)G and E298D polymorphisms were significantly associated with insulin sensitivity (P=0.018, 0.036, 0.039) but were not significant after adjusting for body mass index. ADD1 G460W was associated with insulin sensitivity only after adjusting for body mass index. The NPPA T2238C and SCNN1A A663T were associated with decreased fasting insulin levels after adjusting for body mass index (P=0.015 and 0.028). In conclusion, AGT, NOS3, NPPA, ADRB2, ADD1, and SCNN1A may well be genetic markers for insulin resistance, and adiposity was a potential modifier for only some gene/trait combinations. Our data support the hypothesis that genes in the blood pressure pathway may play a role in insulin resistance in Mexican Americans.

Haplotype analysis of the beta2 adrenergic receptor gene and risk of myocardial infarction in humans

Polymorphisms in the beta2 adrenergic receptor (ADRB2), in particular G16R, Q27E, and T164I, have been implicated in the pathogenesis of cardiovascular and metabolic phenotypes. However, no prospective, genetic-epidemiological data are available on the risk of cardiovascular disease associated with these variants. Using DNA samples collected at baseline in a prospective cohort of 14,916 initially healthy American men, we evaluated the G16R, Q27E, and T164I polymorphisms among 523 individuals who subsequently developed myocardial infarction and among 2092 individuals who remained free of reported cardiovascular events during follow-up. The haplotype frequency distribution was significantly different among cases and controls (chi(2)(7d.f.) = 20.92, P = 0.0039). Haplotype-based logistic regression, adjusting for age, smoking, and randomized treatment group, indicated that G16-Q27-I164 (odds ratio 0.178, 95% C.I. 0.043-0.737, P = 0.017) and (non-G16-Q27)-T164 (odds ratio 1.235, 95% C.I. 1.031-1.480, P = 0.022) haplotypes were significantly associated with altered risk of myocardial infarction. These findings remained after further adjustment for BMI, history of hypertension, and presence or absence of diabetes. In conclusion, variation in haplotype frequencies for the beta2 adrenergic receptor gene was found to be associated with risk of myocardial infarction.

Haplotypes of the ??2-adrenergic receptor gene are associated with essential hypertension in a Singaporean Chinese population

OBJECTIVE

To investigate the relation between the gene encoding the beta2-adrenergic receptor (B2AR) and essential hypertension in a Singaporean Chinese cohort.

METHODS

Three single nucleotide polymorphisms (SNPs) were genotyped in 190 cases and 323 controls, and eight haplotypes were determined and tested for association using the likelihood test statistic.

RESULTS

We observed a significant difference in haplotype frequency distributions between the cases and the controls (P <0.00001). A logistic regression model fitted to the data supported this finding.

CONCLUSION

The results suggest that variants at the B2AR locus may play a role in the pathophysiology of hypertension in this population.

The Arg16/Gly β2-adrenergic receptor polymorphism is associated with altered cardiovascular responses to isometric exercise

A polymorphism in the gene encoding the β2-adrenergic receptor (arginine or glycine at amino acid position 16) is associated with altered vasodilator responses to β2-agonists, which may modulate the pressor response to endogenous catecholamines during stress. To test the hypothesis that the Arg16/Gly polymorphism is associated with differences in acute pressor responses to sympathoexcitation, we measured mean arterial pressure (MAP, Finapres) and heart rate (HR, ECG) during mental stress (MS), cold pressor test (CPT), and handgrip (HG) to fatigue in 31 healthy, nonobese, normotensive adults (mean age ± SE: 31 ± 1; 16 females). Subjects were homozygous for Gly16 ( n = 16) or Arg16 ( n = 15). Both groups had similar baseline MAP (Arg16, 86 ± 3 mmHg; Gly16, 89 ± 2 mmHg; P = 0.4) and HR (Arg16, 68 ± 2 beats/min; Gly16, 65 ± 3 beats/min; P = 0.3). For MS and CPT, MAP and HR did not differ between genotype groups. Handgrip also produced similar increases in MAP; however, the change in HR was greater in the Gly16 homozygotes ( PANOVA= 0.001, genotype-by-time interaction). During HG, peak HR at fatigue was 100 ± 4 beats/min for Gly16 (54% increase from rest) vs. 93 ± 3 beats/min for Arg16 (37% increase). We conclude that the cardiovascular responses to MS and CPT do not differ between Gly16 and Arg16 homozygotes. However, the greater HR response to exercise in the Gly16 homozygotes may serve to maintain the pressor response (increased cardiac output) in the face of augmented peripheral vasodilation (decreased total peripheral resistance) in this group.

Beta2-adrenergic receptor polymorphisms and risk of incident cardiovascular events in the elderly

BACKGROUND

Genetic polymorphisms at codons 16 and 27 of the beta2-adrenergic receptor have been associated with altered response to sympathetic stimulation. We examined these polymorphisms in relation to cardiovascular event risk in the Cardiovascular Health Study.

METHODS AND RESULTS

A total of 808 black and 4441 white participants (mean age, 73 years) were genotyped for the Arg16Gly and Gln27Glu polymorphisms of the beta2-adrenergic receptor. There were 702 incident coronary events, 438 ischemic strokes, and 1136 combined cardiovascular events during 7 to 10 years of follow-up. Allele frequencies differed by race but not by age or hypertension status. Glu27 carriers had a lower risk of coronary events than Gln27 homozygotes (hazard ratio, 0.82; 95% CI, 0.70 to 0.95), and there was a suggestion of decreased risk among Gly16 carriers compared with Arg16 homozygotes (hazard ratio, 0.88; 95% CI, 0.72 to 1.07). There was no association of beta2-adrenergic receptor genotype with ischemic stroke or combined cardiovascular events.

CONCLUSIONS

The Glu27 allele of the beta2-adrenergic receptor was associated with a lower risk of incident coronary events in this elderly population.

Sympathetic control of the circulation in hypertension: lessons from autonomic disorders

PURPOSE OF THE REVIEW

Inappropriate sympathetic overactivity is consistently observed in patients with essential hypertension. The present review summarizes the recent advances that have been made in our understanding of the role of the sympathetic nervous system in hypertension.

RECENT FINDINGS

Studies in patients with autonomic disorders underscore the role of the sympathetic nervous system in the long-term maintenance of hypertension. Abnormalities in the afferent limb of the sympathetic nervous system, in the regulation of central neurons where sympathetic outflow originates, and in the modulation of efferent sympathetic function, can all produce autonomic disorders that are associated with hypertension. More subtle dysfunctions in any of these components have been described in essential hypertension and can contribute to its pathogenesis. These include impaired buffering capacity of arterial baroreflexes, increased central sympathetic outflow, and enhanced norepinephrine release (or decrease reuptake) from sympathetic nerve terminals. Whether genetic polymorphisms of adrenoreceptors are associated with essential hypertension is an area of active research.

SUMMARY

Increased sympathetic activity can contribute to sustained hypertension not only because of its hemodynamic effects (increased cardiac output and vascular resistance), but also by altering renal and water handling by the kidney, and by inducing cardiac and vascular remodeling. Antihypertensive agents that directly or indirectly target this sympathetic overactivity may be particularly useful in long-term treatment of essential hypertension.

Beta-adrenergic receptor polymorphisms: cardiovascular disease associations and pharmacogenetics

The beta-adrenergic receptors (betaAR) play important roles in cardiovascular function and disease, and both agonists and antagonists are widely used in various settings for treatment of cardiovascular disease. Both the beta1AR and beta2AR genes have several polymorphisms that are common in the population and result in encoding of different amino acids. More importantly, in vitro functional studies suggest that these polymorphisms have functional significance. In this review we summarize the literature on the relationship between the betaAR polymorphisms and cardiovascular disease as well as the literature on the impact of these polymorphisms on drug response. Additionally, the polymorphisms in both the beta1AR and beta2AR genes are in linkage disequilibrium; thus, the relevance of single polymorphism vs. haplotype analysis is discussed. Further study of the betaAR genetic polymorphisms is likely to enhance our understanding of cardiovascular disease and improve our use of beta-agonists and beta-antagonists in treatment of cardiovascular disease.

Essential hypertension and beta2-adrenergic receptor gene: linkage and association analysis

A region on human chromosome 5 (5q31.1-qter) contains several genes that encode important blood pressure regulators and thus is a good candidate for analysis of linkage and association with hypertension. We recruited 638 individuals from 212 Polish pedigrees with clustering of essential hypertension. These subjects were genotyped for 11 microsatellite markers that span this region to test for linkage to essential hypertension and systolic and diastolic blood pressures. The segment of this region of approximately 7 cM delineated by D5S1480 and D5S500 markers was linked to blood pressures in multipoint analysis. In 2-point analysis, D5S1480--the marker in close proximity to beta2-adrenergic receptor gene--reached the maximal linkage to essential hypertension and adjusted systolic and diastolic blood pressures, implicating this gene as a positional candidate for further association studies. Arg16Gly, Gln27Glu, and Thr164Ile--3 functional single nucleotide polymorphisms within the beta2-adrenergic receptor gene--were tested for association with essential hypertension. None of these polymorphisms showed a significant association with essential hypertension, separately or in the haplotype analysis. This study provided evidence of linkage of 5q31.1-5qter region to essential hypertension in the European population. Moreover, it implicated the chromosomal segment in close proximity to D5S1480 and D5S500. The detailed analysis of 3 single nucleotide polymorphisms does not support the role of the beta2-adrenergic receptor gene as a major causative gene for the detected linkage.