Identification of adrenergic receptor polymorphisms

Markers for predicting the efficacy of beta-blockers in vasovagal syncope management in children: A mini-review

Vasovagal syncope (VVS) is a common subtype of neurally mediated syncope. It is prevalent in children and adolescents, and critically affects the quality of life of patients. In recent years, the management of pediatric patients with VVS has received extensive attention, and β-blocker serves as an important choice of the drug therapy for children with VVS. However, the empirical use of β-blocker treatment has limited therapeutic efficacy in patients with VVS. Therefore, predicting the efficacy of β-blocker therapy based on biomarkers related to the pathophysiological mechanism is essential, and great progress has been made by applying these biomarkers in formulating individualized treatment plans for children with VVS. This review summarizes recent advances in predicting the effect of β-blockers in the management of VVS in children.

Adrenergic Polymorphisms and Survival in African Americans With Heart Failure: Results From A-HeFT

BACKGROUND

Polymorphisms in adrenergic signaling affect the molecular function of adrenergic receptors and related proteins. The β1 adrenergic receptor (ADRB1) Arg389Gly, G-protein receptor kinase type 5 (GRK5) Gln41Leu, G-protein β-3 subunit (GNB3) 825 C/T, and α2c deletion affect adrenergic tone, impact heart failure outcomes and differ in prevalence by ethnicity. Their combined effect within black cohorts remains unknown.

METHODS AND RESULTS

We analyzed subjects from the African American Heart Failure Trial (A-HeFT) by assessing event-free survival, quality of life, and gene coinheritance. Significant coinheritance effects on survival included GRK5 Leu41 among subjects co-inheriting GNB3 825 C alleles (n = 166, 90.4% vs 69.0%, P < 0.001). By contrast, the impact of ADRB1 Arg389Arg genotype was magnified among subjects with GNB3 825 TT genotype (n = 181, 66.3% vs 85.7%, P = .002). The lack of the α2c deletion (ie, insertion) led to a greater impact of the ARG389Arg genotype (n = 289, 76.4% vs 86.1%, P = .007).

CONCLUSIONS

Polymorphisms in adrenergic signaling affects outcomes in black subjects with heart failure. Coinheritance patterns in genetic variation may help determine heart failure survival.

Pharmacogenetics and healthcare outcomes in patients with chronic heart failure

PURPOSE

To test for associations between genetic polymorphisms of adrenergic receptors (AR) and other candidate genes and healthcare utilization in heart failure patients, taking into account other important factors, such as medication adherence.

METHODS

One year-hospital utilization data were collected from 140 participants with heart failure, aged 50 years or older. Medication adherence was measured. Hospitalization and emergency department (ED) visits due to heart failure were used as healthcare outcomes. The genotypes of polymorphisms in six genes were determined: α(2C)-AR (ADRA2C), β₁-AR (ADRB1), β₂-AR (ADRB2), endothelial nitric oxide synthase (eNOS), angiotensin converting enzyme (ACE), and CYP4A11. Haplotypes for ADRB1 and ADRB2 were estimated. The genotype effects on healthcare outcomes were examined using log-linear regression models.

RESULTS

Compared to ADRB1 Arg389 carriers, homozygous Gly389Gly carriers experienced fewer ED visits [incidence rate ratio (IRR) 0.07, 95 % confidence interval (CI) 0.01-0.54, P = 0.022]. Compared to ADRB2 homozygous Gly16Gly carriers, Arg16Gly carriers had fewer ED visits (IRR 0.23, 95 % CI 0.09-0.59, P = 0.006). Polymorphisms in ADRB1 as well as those in ADRB2 were in linkage disequilibrium, with three defining haplotypes, respectively. For ADRB2, the risk of hospitalizations and ED visits were relatively lower in Arg16/Gln27 carriers but relatively higher in homozygous Gly16/Gln27 carriers (P < 0.05). Compared to eNOS 894TT homozygous variants, 894GG and 894GT carriers had notably fewer ED visits (IRR 0.05, 95 % CI 0.01-0.25, P = 0.0013 and IRR 0.10, 95 % CI 0.02-0.42, P = 0.006, respectively). The other polymorphisms showed no association with healthcare outcomes.

CONCLUSIONS

After controlling for demographics, functional status, and treatment adherence, polymorphisms in ADRB1, ADRB2 and eNOS are associated with healthcare outcomes in heart failure patients.

Single-nucleotide polymorphisms in the β-adrenergic receptor genes are associated with lung allograft utilization

BACKGROUND

Pulmonary edema and associated impaired oxygenation are a major reason for rejection of donor lung allografts offered for transplantation. Clearance of pulmonary edema can be upregulated by stimulation of β-adrenergic receptors (βARs). Single-nucleotide polymorphisms (SNPs) in βAR genes have functional effects in vitro and in vivo. We hypothesized that SNPs in βAR genes would be associated with rates of utilization of donor lung allografts offered for transplantation.

METHODS

Nine hundred fifty-one organ donors were genotyped for 4 amino-acid-coding SNPs in the βAR genes. Lung allograft utilization was compared among donors stratified by genotypes.

RESULTS

Utilization of donor lung allografts was 55% vs 35% (p = 0.02) among donors with GG vs AA/AG genotypes of the Ser49Gly SNP, 39% vs 32% (p = 0.04) with GG vs AA/AG genotype of Gly16Arg SNP and 37% vs 32% (p = 0.1) with CC vs GC/GG genotype of the Arg389Gly SNP. In the combined analysis, donors carrying 0 or 1 associated genotype had a utilization rate of 33%, whereas donors carrying 2 or 3 associated genotypes had utilization rates of 44% and 58%, respectively (p = 0.008). There was a stepwise decrease in chest radiograph infiltrates and an increase in partial pressure of oxygen/fraction of inspired oxygen (PaO(2)/FIO(2)) with an increasing number of these associated genotypes.

CONCLUSION

Genetic variants in the βAR genes among organ donors are associated with higher rates of lung allograft utilization. The increased utilization may be related to increased clearance of pulmonary edema and improved oxygenation in donors with favorable genotypes and suggests that βAR agonists may have a role in donor management.

Adrenergic receptor polymorphisms in patients with stress (tako-tsubo) cardiomyopathy

BACKGROUND

Stress (tako-tsubo) cardiomyopathy (SC) is a newly reported condition afflicting older women, characterized by acute left ventricular (LV) systolic dysfunction, triggered by emotionally and physically stressful events, and occurring without significant coronary obstruction. Sympathetic nervous system hyperactivity has been implicated in the pathophysiology of SC. Single nucleotide polymorphisms involving the adrenergic receptors (AR) might result in susceptibility to SC.

METHODS

Forty-one female SC patients were identified aged 34-89 years (mean 65) and were compared with 43 control females of similar age with respect to AR genotype frequencies for B1 receptor (amino acid positions 389 and 49) and alpha 2c receptor (deletion 322-325).

RESULTS

For SC patients, initial LV ejection fraction was 32 ± 10% vs. 62 ± 11% in control patients, p < 0.05. Genotype frequencies for SC patients vs. controls were B1 389 Arg/Arg (0.49 vs. 0.51), B1 389 Arg/Gly (0.49 vs. 0.49), B1 389 Gly/Gly (0.02 vs. 0), B1 49 Ser/Ser (0.88 vs. 0.81), B1 49 Ser/Gly (0.12 vs. 0.16), B1 49 Gly/Gly (0 vs. 0.02), alpha 2c Wt/Wt (0.93 vs. 0.86), and alpha 2c Wt/Del 322-325 (0.07 vs. 0.14); p = ns for all comparisons.

CONCLUSIONS

Genotype polymorphism frequencies for B1 receptor (amino acid positions 389 and 49) and alpha 2c receptor (deletion 322-325) are not significantly different in SC patients compared to female controls. These data suggest that these AR polymorphisms do not mediate the sympathetic nervous system hyperactivity in SC patients.

Genetics of beta2-adrenergic receptors and the cardiopulmonary response to exercise

Exercise elicits a number of physiologic responses to increase oxygen delivery to working muscles. The beta2-adrenergic receptors (ADRB2) play a role in the cardiopulmonary response to exercise. This review is focused on how the gene that encodes the ADRB2 influences the cardiopulmonary response to exercise. In addition, we discuss possible interactions between ADRB2 and other genes important in exercise performance.

Clinical consequences of ADRbeta2 polymorphisms

The most prescribed medication for controlling bronchoconstriction associated with asthma and chronic obstructive pulmonary disease are beta-agonists. The gene ADRbeta2 encodes the beta-2-adrenergic receptor and contains several common genetic variations that affect gene expression and receptor function in vitro. The ADRbeta2 variations Gly(16)Arg and Gln(27)Glu and, more recently, haplotypic variations, have been the focus of numerous pharmacogenetic studies looking at responses to short-acting (SABA) and long-acting beta-agonists (LABA) in subjects with asthma. Thus far, a consensus on the effects of ADRbeta2 genetic variations has not been reached, although there does appear to be a reproducible adverse effect in subjects homozygous for Arg(16) that are regularly treated with SABAs. The complexity of the genotype by response effects observed makes clinical application of ADRbeta2 genetic variations limited, and may require the use of detailed haplotypic variation to fully understand the role ADRbeta2 plays in regulating beta-agonist response.

Alveolar epithelial beta2-adrenergic receptors

beta(2)-adrenergic receptors are present throughout the lung, including the alveolar airspace, where they play an important role for regulation of the active Na(+) transport needed for clearance of excess fluid out of alveolar airspace. beta(2)-adrenergic receptor signaling is required for up-regulation of alveolar epithelial active ion transport in the setting of excess alveolar edema. The positive, protective effects of beta(2)-adrenergic receptor signaling on alveolar active Na(+) transport in normal and injured lungs provide substantial support for the use of beta-adrenergic agonists to accelerate alveolar fluid clearance in patients with cardiogenic and noncardiogenic pulmonary edema. In this review, we summarize the role of beta(2)-adrenergic receptors in the alveolar epithelium with emphasis on their role in the regulation of alveolar active Na(+) transport in normal and injured lungs.

A polymorphism within a conserved beta(1)-adrenergic receptor motif alters cardiac function and beta-blocker response in human heart failure

Heterogeneity of heart failure (HF) phenotypes indicates contributions from underlying common polymorphisms. We considered polymorphisms in the beta(1)-adrenergic receptor (beta(1)AR), a beta-blocker target, as candidate pharmacogenomic loci. Transfected cells, genotyped human nonfailing and failing ventricles, and a clinical trial were used to ascertain phenotype and mechanism. In nonfailing and failing isolated ventricles, beta(1)-Arg-389 had respective 2.8 +/- 0.3- and 4.3 +/- 2.1-fold greater agonist-promoted contractility vs. beta(1)-Gly-389, defining enhanced physiologic coupling under relevant conditions of endogenous expression and HF. The beta-blocker bucindolol was an inverse agonist in failing Arg, but not Gly, ventricles, without partial agonist activity at either receptor; carvedilol was a genotype-independent neutral antagonist. In transfected cells, bucindolol antagonized agonist-stimulated cAMP, with a greater absolute decrease observed for Arg-389 (435 +/- 80 vs. 115 +/- 23 fmol per well). Potential pathophysiologic correlates were assessed in a placebo-controlled trial of bucindolol in 1,040 HF patients. No outcome was associated with genotype in the placebo group, indicating little impact on the natural course of HF. However, the Arg-389 homozygotes treated with bucindolol had an age-, sex-, and race-adjusted 38% reduction in mortality (P = 0.03) and 34% reduction in mortality or hospitalization (P = 0.004) vs. placebo. In contrast, Gly-389 carriers had no clinical response to bucindolol compared with placebo. Those with Arg-389 and high baseline norepinephrine levels trended toward improved survival, but no advantage with this allele and exaggerated sympatholysis was identified. We conclude that beta(1)AR-389 variation alters signaling in multiple models and affects the beta-blocker therapeutic response in HF and, thus, might be used to individualize treatment of the syndrome.

Molecular mechanisms of beta2-adrenergic receptor function and regulation

It is now clear that the beta2-adrenergic receptor continuously oscillates between various conformations in the basal state, and that agonists act to stabilize one or more conformations. It is conceivable that synthetic agonists might be engineered to preferentially confine the receptor to certain conformations deemed clinically important while having a less stabilizing effect on unwanted conformations. In addition, studies of genetically engineered mice have revealed previously unrecognized cross-talk between the beta2-receptor and phospholipase C, such that removal of the primary dilating pathway results in downregulation of constrictive pathways and overactivity of the dilating pathway increases the contractile response. These results indicate a dynamic interaction between beta2-receptor activity and Gq-coupled receptors that constrict the airway. Potentially, then, during chronic beta-agonist therapy, expression of phospholipase C is increased, the functions of Gq-coupled constrictive receptors are enhanced, and there may be an increased tendency for clinical decompensation due to asthma and chronic obstructive pulmonary disease triggers. Antagonists to these receptors might be able to act synergistically with chronic beta-agonists to block the effect of phospholipase C. Alternatively, perhaps novel phospholipase C antagonists would provide the most efficacious approach to blocking the physiologic sequelae of cross-talk between the beta2-receptor and phospholipase C.

Functional adrenergic receptor polymorphisms and idiopathic orthostatic intolerance

OBJECTIVES

Idiopathic orthostatic intolerance (IOI) is a common disorder that is characterized by chronic orthostatic symptoms and substantial increases in heart rate and plasma norepinephrine concentrations that are disproportionately high while standing. Several features of the syndrome, including the tachycardia, tremulousness, and exaggerated norepinephrine have been considered potentially due to hypoactive or hyperactive states of adrenergic receptors of the sympathetic nervous system. The aim of this study was therefore to ascertain whether genotypes at eight polymorphic loci within five relevant adrenergic receptor genes (alpha2A, alpha2B, alpha2C, beta1 and beta2) influence the risk for IOI.

METHODS

We studied 80 young men in military service (20 patients with IOI and 60 age-matched controls). All participants underwent a tilt table test including monitoring of blood pressure, heart rate and plasma catecholamines, in the supine position and during 30 min of standing. Genotyping at the eight loci (alpha2ALys251, alpha2BDel301-303, alpha2CDel322-325, beta1Gly49, beta1Arg389, beta2Arg16, beta2Glu27, beta2Ile164) was performed in all participants. Chi-square tests of independence were used to test for associations between IOI and genotype. In addition, an association of the polymorphisms with haemodynamic variables (heart rate, supine and upright blood pressure) was ascertained using one-way variance analysis.

RESULTS

For the beta1Gly49 polymorphism we found a decrease in the risk of IOI among persons who were homozygous (odds ratio, 0.88; 95% confidence interval, 0.81-0.97). In addition, we found an association between beta1Gly49 and decreased heart rate in the upright position, regardless of IOI diagnosis. There were no associations with the other studied polymorphisms and IOI.

CONCLUSIONS

Our current results suggest that the beta1Gly49 polymorphism is protective for IOI. This is likely one of several common genetic loci that may represent modifiers of IOI phenotypes.

Beta2-adrenoceptor Thr164Ile polymorphism is associated with markedly decreased vasodilator and increased vasoconstrictor sensitivity in vivo

BACKGROUND

The uncommon Thr164Ile polymorphism of the beta2-adrenoceptor is associated with profoundly altered responses to agonist in vitro; however its effects on vascular responses in vivo are not known. Altered adrenergic vascular sensitivity may contribute to the decreased survival observed in patients with congestive heart failure carrying the Ile164 allele.

METHODS AND RESULTS

We used the linear variable differential transformer dorsal hand vein technique to compare vasodilation in response to the beta-adrenergic receptor agonist, isoproterenol, and vasoconstriction in response to the alpha-adrenergic receptor agonist, phenylephrine, in healthy homozygous (Thr164/Thr164) (n = 21) and heterozygous Thr164/Ile164 (n = 5) women. The dose of isoproterenol required to achieve 50% venodilation (geometric mean; 95% CI) was significantly higher in women with the Ile164 allele (82.5 ng/min; 17.3-394 ng/min) than those without (15.8 ng/min; 11-25 ng/min; P = 0.004). The maximum response to isoproterenol was not different (102 +/- 1% and 102 +/- 3%, respectively, P = 0.9). The dose of phenylephrine needed to induce 50% venoconstriction was significantly lower in women with the Ile164 allele (151 ng/min; 42-543 ng/min) than those without (540 ng/min; 350-835 ng/min; P = 0.02).

CONCLUSIONS

The Thr164Ile polymorphism of the beta2-adrenergic receptor is associated with a five-fold reduction in sensitivity to beta2 receptor agonist-mediated vasodilation; vasoconstrictor sensitivity is increased. The overall effect of the Thr164Ile polymorphism is to shift the balance of adrenergic vascular tone toward vasoconstriction. This suggests a mechanistic explanation for the clinical observation of decreased survival in patients with congestive heart failure heterozygous for the Thr164Ile polymorphism.

Association of beta-adrenergic receptor polymorphisms and progression to heart failure in patients with idiopathic dilated cardiomyopathy

PURPOSE

Increased sympathetic nervous system activation via the beta-adrenergic pathway influences the evolution of idiopathic dilated cardiomyopathy. We assessed the effects of beta-adrenergic receptor variants on heart failure in idiopathic dilated cardiomyopathy.

METHODS

We prospectively analyzed 171 consecutive patients (mean [+/- SD] age, 49 +/- 14 years; 129 men) with idiopathic dilated cardiomyopathy who were receiving conventional treatment. All were characterized by polymerase chain reaction-restriction fragment length polymorphism analysis for Ser49Gly and Arg389Gly in the beta1-adrenergic receptor; the 5' leader cistron (LC) Arg19Cys, Arg16Gly, Gln27Glu, and Thr164Ile in the beta2-adrenergic receptor; and Arg64Trp in the beta3-adrenergic receptor. The endpoint was heart failure, defined as a worsening of clinical condition leading to hospitalization for heart failure, cardiac transplantation, or death from heart failure.

RESULTS

During a median follow-up of 33 months, 24 patients had heart failure. In a Cox univariate analysis, the beta1Gly49 and beta2 5'LC-Cys19, Arg16, and Gln27 alleles were associated with a lower risk of heart failure. In a multivariate analysis that considered age, functional class, left ventricular ejection fraction, and beta-blocker use, three beta2-adrenergic receptor alleles were associated with lower risk: 5'LC-Cys19 (hazard ratio [HR]: 0.15; 95% confidence interval [CI]: 0.05 to 0.42), Arg16 (HR: 0.12; 95% CI: 0.04 to 0.35), and Gln27 (HR: 0.15; 95% CI: 0.05 to 0.42).

CONCLUSION

The Gly49 allele in the beta1-adrenergic receptor and the 5' LC-Cys19, Arg16, and Gln27 alleles in the beta2-adrenergic receptor were associated with a lower risk of heart failure in idiopathic dilated cardiomyopathy, suggesting that the beta1- and beta2-adrenergic receptor genes are modifier genes.

Polymorphisms of adrenergic receptors: variations on a theme

Recent studies have revealed that most of the adrenergic receptor genes are polymorphic, leading to changes in the amino sequence of the encoded receptor. The variations occur in multiple functional regions of the receptors, and appear as haplotypes with other coding and noncoding polymorphisms in their genes. The consequences of such genetic variability have been explored in recombinant cell-based systems and in human studies. Adrenergic receptor polymorphisms have been shown to alter receptor binding, G-protein coupling, regulation, and expression compared with their allelic counterparts. Here, the genetic and molecular characterization of these polymorphisms is reviewed, as well as their potential impact on pharmacogenetics, disease risk, and disease modification.

Adrenergic receptor knockout mice: distinct functions of 9 receptor subtypes

The biological effects of epinephrine and norepinephrine are mediated via 9 different adrenergic receptor subtypes, which all belong to the superfamily of G protein-coupled receptors. Although pharmacological ligands for adrenergic receptors have an important place in medical therapy, the full therapeutic potential of the 9 adrenergic receptor subtypes has not been explored yet. To dissect the physiological relevance of adrenergic receptor subtype diversity, gene-targeted mouse models carrying deletions in these receptor genes ("knockout mice") have been generated. This review gives an overview of the phenotypes observed in mice deficient in adrenergic receptors and discusses the therapeutic relevance of subtype-specific drug therapy.

Activity of the uptake-1 norepinephrine transporter as measured by I-123 MIBG in heart failure patients with a loss-of-function polymorphism of the presynaptic alpha2C-adrenergic receptor

BACKGROUND

Patients with a deletion of 4 consecutive amino acids in the gene encoding for the alpha(2C)-adrenergic receptor (alpha(2C)Del322-325) have an increased prevalence of clinical heart failure, worse clinical status, and a lower left ventricular ejection fraction compared with patients without this deletion. We postulated that patients with the alpha(2C)Del322-325 polymorphism would have a compensatory increase in norepinephrine uptake-1 transporter activity as measured by iodine 123 metaiodobenzylguanidine (MIBG).

METHODS AND RESULTS

Thirty-nine patients with heart failure related to idiopathic dilated cardiomyopathy were studied. Demographic characteristics, left ventricular ejection fraction, maximum oxygen consumption, exercise duration, and plasma norepinephrine levels did not differ between patients with the alpha(2C) receptor polymorphism (n = 9) and those without it (n = 30). Patients with the alpha(2C)Del322-325 polymorphism had significantly greater heart-to-mediastinum ratios of I-123 MIBG at 4 hours after tracer injection (1.60 +/- 0.19 vs 1.41 +/- 0.19, P =.0117) and greater background-corrected heart counts per pixel at 4 hours compared with patients without the polymorphism.

CONCLUSIONS

Patients with genetic impairment of the alpha(2C)-adrenergic receptor have augmented activity of the norepinephrine uptake-1 transporter as measured by I-123 MIBG. Further studies are needed to clarify the mechanism by which uptake-1 transporter activity is increased in this setting.

β1-adrenergic receptor polymorphisms confer differential function and predisposition to heart failure

Catecholamines stimulate cardiac contractility through beta(1)-adrenergic receptors (beta(1)-ARs), which in humans are polymorphic at amino acid residue 389 (Arg/Gly). We used cardiac-targeted transgenesis in a mouse model to delineate mechanisms accounting for the association of Arg389 with human heart failure phenotypes. Hearts from young Arg389 mice had enhanced receptor function and contractility compared with Gly389 hearts. Older Arg389 mice displayed a phenotypic switch, with decreased beta-agonist signaling to adenylyl cyclase and decreased cardiac contractility compared with Gly 389 hearts. Arg389 hearts had abnormal expression of fetal and hypertrophy genes and calcium-cycling proteins, decreased adenylyl cyclase and G alpha(s) expression, and fibrosis with heart failure This phenotype was recapitulated in homozygous, end-stage, failing human hearts. In addition, hemodynamic responses to beta-receptor blockade were greater in Arg389 mice, and homozygosity for Arg389 was associated with improvement in ventricular function during carvedilol treatment in heart failure patients. Thus the human Arg389 variant predisposes to heart failure by instigating hyperactive signaling programs leading to depressed receptor coupling and ventricular dysfunction, and influences the therapeutic response to beta-receptor blockade.

Pharmacology and physiology of human adrenergic receptor polymorphisms

Adrenergic receptors are expressed on virtually every cell type in the body and are the receptors for epinephrine and norepinephrine within the sympathetic nervous system. They serve critical roles in maintaining homeostasis in normal physiologic settings as well as pathologic states. These receptors are also targets for therapeutically administered agonists and antagonists. Recent studies have shown that at least seven adrenergic receptor subtypes display variation in amino acid sequence in the human population due to common genetic polymorphisms. Variations in potential regulatory domains in noncoding sequence are also present. Here, we review the consequences of these polymorphisms in terms of signaling, human physiology and disease, and response to therapy.

Polymorphisms of the beta1-adrenergic receptor predict exercise capacity in heart failure

BACKGROUND

Exercise performance in patients with congestive heart failure is partially dependent on cardiac beta1-adrenergic receptor (beta1AR) function. There are 2 common polymorphisms of the beta1AR gene that alter the encoded amino acids at positions 49 (Ser or Gly) and 389 (Gly or Arg) and alter receptor function in vitro. Their relevance to modification of cardiac function in heart failure is not known.

METHODS

Exercise testing was performed in 263 patients with idiopathic or ischemic cardiomyopathy (left ventricular ejection fraction approximately 25%). Potential associations were sought between beta1AR genotypes and the primary outcome variables of peak oxygen consumption (VO2), heart rate response, and exercise time.

RESULTS

The major determinants of exercise capacity were the polymorphisms at position 389, where patients homozygous for Gly389 had significantly lower peak VO2 compared with those with Arg389 (14.5 +/- 0.6 vs 17.7 +/- 0.4 mL/kg/min, P =.006), despite similar clinical characteristics including left ventricular ejection fraction. Consistent with a gene dose-response, heterozygosity was associated with an intermediate response (16.9 +/- 0.6 mL/kg/min, P <.05). When position 49 genotypes were included, a graded relationship between the 5 2-locus haplotypes and VO2 was found. Two haplotypes displayed the most divergent peak VO2: homozygous Gly389/Ser49, and homozygous Arg389/Gly49 carriers (14.4 +/- 0.5 vs 18.2 +/- 0.8 mL/kg/min, P =.001). Genotype did not predict the heart rate response. The above results were independent of beta-blocker or other medication use, left ventricular ejection fraction, beta2AR genotype, or other demographic and clinical characteristics.

CONCLUSION

beta1AR polymorphisms are a significant determinant of exercise capacity in patients with congestive heart failure. Early identification, by genetic testing for these polymorphisms, of heart failure patients at risk for development of depressed exercise capacity may be useful for initiation of specific therapy tailored to genotype.

Synergistic polymorphisms of beta1- and alpha2C-adrenergic receptors and the risk of congestive heart failure

BACKGROUND

Sustained cardiac adrenergic stimulation has been implicated in the development and progression of heart failure. Release of norepinephrine is controlled by negative feedback from presynaptic alpha2-adrenergic receptors, and the targets of the released norepinephrine on myocytes are beta1-adrenergic receptors. In transfected cells, a polymorphic alpha2C-adrenergic receptor (alpha2CDel322-325) has decreased function, and a variant of the beta1-adrenergic receptor (beta1Arg389) has increased function. We hypothesized that this combination of receptor variants, which results in increased synaptic norepinephrine release and enhanced receptor function at the myocyte, would predispose persons to heart failure.

METHODS

Genotyping at these loci was performed in 159 patients with heart failure and 189 controls. Logistic-regression methods were used to determine the potential effect of each genotype and the interaction between them on the risk of heart failure.

RESULTS

Among black subjects, the adjusted odds ratio for heart failure among persons who were homozygous for alpha2CDel322-325 as compared with those with the other alpha2C-adrenergic receptor genotypes was 5.65 (95 percent confidence interval, 2.67 to 11.95; P<0.001). There was no increase in risk with beta1Arg389 alone. However, there was a marked increase in the risk of heart failure among persons who were homozygous for both variants (adjusted odds ratio, 10.11; 95 percent confidence interval, 2.11 to 48.53; P=0.004). The patients with heart failure did not differ from the controls in the frequencies of nine short tandem-repeat alleles. Among white subjects, there were too few who were homozygous for both polymorphisms to allow an adequate assessment of risk.

CONCLUSIONS

The alpha2CDel322-325 and beta1Arg389 receptors act synergistically to increase the risk of heart failure in blacks. Genotyping at these two loci may be a useful approach for identification of persons at risk for heart failure or its progression, who may be candidates for early preventive measures.

Novel and nondetected human signaling protein polymorphisms

The frequency of single nucleotide polymorphisms (SNPs) in downstream signaling proteins was determined by combination heteroduplex HPLC and double-stranded sequencing of genomic DNA from 96-144 congestive heart failure (CHF) patients. Analysis of 56 coding exons in 9 signaling genes revealed 17 novel and 8 previously reported synonymous (no change in amino acid) SNPs, as well as one novel nonsynonymous SNP in the Rad small G protein. Because this initial analysis failed to detect numerous SNPs reported in the NCBI and Celera databases, double-strand sequencing of relevant exons from 74-91 CHF patients was used to confirm the absence of 10 previously reported nonsynonymous SNPs. Our results show that synonymous SNPs are frequent in signaling protein genes, whereas nonsynonymous SNPs are rare, suggesting a high degree of evolutionary conservation among these downstream signaling molecules. Comparisons of our results to the NCBI and Celera databases indicates that 56% of their SNP entries are not detected in our cohort. Importantly, while 31% of database SNPs were verified, 69% of SNPs detected in our cohort are not included in these databases. These findings indicate that caution may be warranted in relying exclusively on SNP databases as catalogs for polymorphic signaling protein genes.

False positive non-synonymous polymorphisms of G-protein coupled receptor genes

Polymorphisms of G-protein coupled receptor (GPCR) genes are associated with disease risk and modification, and the response to receptor-directed therapy. Genomic sequencing ( approximately 1700 automated runs) from as many as 120 chromosomes from 60 multiethnic individuals was performed to confirm non-synonymous coding polymorphisms reported in the dbSNP database from 25 randomly selected GPCR genes. These polymorphisms were in regions of the receptors responsible for structural integrity, ligand binding, G-protein coupling and phosphoregulation. However, most of these putative polymorphisms could not be confirmed (false positive rate of 68%). Based on these results, we suggest that the variability of the superfamily is not well defined, and we caution against exclusive reliance on databases for selection of candidate GPCR polymorphisms for disease association and pharmacogenetic studies.