beta(2)-adrenergic receptor Arg16/Arg16 genotype is associated with reduced lung function, but not with asthma, in the Hutterites

Potential Metabolic Biomarkers in Adult Asthmatics

Asthma is the most common chronic airway inflammation, with multiple phenotypes caused by complicated interactions of genetic, epigenetic, and environmental factors. To date, various determinants have been suggested for asthma pathogenesis by a new technology termed omics, including genomics, transcriptomics, proteomics, and metabolomics. In particular, the systematic analysis of all metabolites in a biological system, such as carbohydrates, amino acids, and lipids, has helped identify a novel pathway related to complex diseases. These metabolites are involved in the regulation of hypermethylation, response to hypoxia, and immune reactions in the pathogenesis of asthma. Among them, lipid metabolism has been suggested to be related to lung dysfunction in mild-to-moderate asthma. Sphingolipid metabolites are an important mediator contributing to airway inflammation in obese asthma and aspirin-exacerbated respiratory disease. Although how these molecular variants impact the disease has not been completely determined, identification of new causative factors may possibly lead to more-personalized and precise pathway-specific approaches for better diagnosis and treatment of asthma. In this review, perspectives of metabolites related to asthma and clinical implications have been highlighted according to various phenotypes.

Beta 2 Adrenergic Receptor Genetic Polymorphisms in Bronchial Asthma: Relationship to Disease Risk, Severity, and Treatment Response

BACKGROUND

The β₂-adrenergic receptor gene is one of the most extensively studied genes with respect to asthma prevalence and severity. The Arg16Gly and Gln27Glu polymorphisms in the β₂-adrenergic receptor gene cause changes in the amino acids sequence of the receptor which may cause alteration in response to bronchodilators and the risk of asthma.

OBJECTIVE

The purpose of the study was to determine the association between β₂-adrenergic receptor gene polymorphisms and asthma risk, severity and response to therapy.

SUBJECTS AND METHODS

58 asthmatic patients and 38 healthy subjects were included. The β₂-adrenergic receptor polymorphisms genotyping was done using Real-Time polymerase chain reaction.

RESULTS

The allelic frequencies for the Arg16Gly polymorphism were 15.5%, 48.3%, and 36.2% for the homozygous A wild, heterozygous, and homozygous G mutant alleles in asthmatics (P < 0.01) and 5.3%, 47.4%, and 47.4% in healthy subjects (P < 0.01). For the Gln27Glu polymorphism, the allelic frequencies for the homozygous C wild, heterozygous and homozygous G mutant alleles were 51.7%, 41.4%, and 6.9% in asthmatics (P < 0.01) and 44.7%, 39.5%, and 15.8% in healthy subjects (P < 0.01). The heterozygous Arg16Gly and Gln27Glu were found in most of severe asthma cases (7/13, 53.8% each). While homozygous wild and mutant seemed to be protective and associated with mild disease in both alleles. Finally, 75% of Arg16Gly heterozygous group were good responders (P < 0.01), 81% of homozygous G mutant were bad responders. For Gln27Glu polymorphism, 60% of C wild group were good responders and 75% of G mutant group were bad responders.

CONCLUSIONS

The findings suggest that the Arg16Gly and Gln27Glu polymorphisms in the β2-AR gene are associated with asthma severity and response to therapy and might be used in personalized treatment for these patients in the future. This work is registered in ClinicalTrial.gov with ID: NCT03118869.

Polymorphisms in Beta-2 Adrenergic Receptor Gene and Association with Tuberculosis

PURPOSE

Genetic susceptibility for tuberculosis in human has been previously demonstrated. Polymorphisms in genes involved in immune responses may alter the susceptibility of individuals to tuberculosis. Polymorphisms of beta-2 adrenergic receptor (ADRB2) gene can be possibly an important risk factor in tuberculosis. In this study, the association between rs1042713 (Arg16Gly +46A>G) and rs1042714 (Gln27Glu +79C>G) polymorphisms in ADRB2 gene and tuberculosis was evaluated.

METHODS

Genotype distributions of the rs1042713 (Arg16Gly +46A>G) and rs1042714 (Gln27Glu +79C>G) polymorphisms in ADRB2 gene in 106 patients with pulmonary tuberculosis and 88 healthy subjects were studied by PCR-RFLP method in an Iranian population.

RESULTS

The frequency of rs1042713*G and rs1042714*G alleles in ADRB2 gene in tuberculosis patients was significantly different from healthy controls [odds ratio (OR) 0.176, 95% confidence interval (CI) 0.065-0.48, P value <0.001 and OR 0.45, 95% CI 0.247-0.825, P value = 0.009, respectively]. There were no significant differences in haplotype analysis between the patients and control subjects.

CONCLUSION

The association was reported between rs1042713 and rs1042714 polymorphisms in ADRB2 gene and tuberculosis for the first time. rs1042713*G and rs1042714*G polymorphisms in ADRB2 gene makes people more susceptible to develop the disease.

Asthma Phenotypes in Japanese Adults - Their Associations with the CCL5 ADRB2 Genotypes

BACKGROUND

Cluster analyses were previously performed to identify asthma phenotypes underlying asthma syndrome. Although a large number of patients with asthma develop the disease later in life, these previous cluster analyses focused mainly patients with younger-onset asthma.

METHODS

Cluster analysis examined the existence of distinct phenotypes of late-onset asthma in Japanese patients with adult asthma. We then associated genotypes at the CCL5, TSLP, IL4, and ADRB2 genes with the clusters of asthma identified.

RESULTS

Using the 8 variables of age, sex, age at onset of the disease, smoking status, total serum IgE, %FEV1, FEV1/FVC, and specific IgE responsiveness to common inhaled allergens, two-step cluster analysis of 880 Japanese adult asthma patients identified 6 phenotypes: cluster A (n = 155): older age at onset, no airflow obstruction; cluster B (n = 170): childhood onset, normal-to-mild airflow obstruction; cluster C (n = 119): childhood onset, the longest disease duration, and moderate-to-severe airflow obstruction; cluster D (n = 108): older age at onset, severe airflow obstruction; cluster E (n = 130): middle-age at onset, no airflow obstruction; and cluster F (n = 198): older age at onset, mild-to-moderate airflow obstruction. The CCL5-28C>G genotype was significantly associated with clusters A, B and D (OR 1.65, p = 0.0021; 1.67, 0.018; and 1.74, 0.011, respectively). The ADRB2 Arg16Gly genotype was also associated with clusters B and D (OR 0.47, p = 0.0004; and 0.63, 0.034, respectively).

CONCLUSIONS

The current cluster analysis identified meaningful adult asthma phenotypes linked to the functional CCL5 and ADRB2 genotypes. Genetic and phenotypic data have the potential to elucidate the pheno- typic heterogeneity and pathophysiology of asthma.

Loss of salmeterol bronchoprotection against exercise in relation to ADRB2 Arg16Gly polymorphism and exhaled nitric oxide

RATIONALE

β2-Agonists are the treatment of choice for exercise-induced bronchoconstriction (EIB) and act through specific receptors (ADRB2). Arg16Gly polymorphisms have been shown to affect responses to regular use of β2-agonists.

OBJECTIVES

To evaluate the influence of the Arg16Gly receptor polymorphism on salmeterol bronchoprotection in EIB and assess predictors of bronchoprotection.

METHODS

A prospective, genotype-blinded, randomized trial was performed in 26 subjects (12 Arg16Arg and 14 Gly16Gly) with EIB who were not on controller therapy. Subjects were administered salmeterol, 50 μg twice a day for 2 weeks, and underwent an exercise challenge 9 hours after the first and last drug dose. In addition to genotype, FEV1, response to salmeterol, degree of EIB, and exhaled nitric oxide (FE(NO)) at baseline were examined for their association with loss of bronchoprotection (LOB).

MEASUREMENTS AND MAIN RESULTS

The maximum exercise-induced FEV1 fall was 27.9 ± 1.4% during the run-in period, 8.1 ± 1.2% (70.3 ± 4.1% bronchoprotection) after the first salmeterol dose, and 22.8 ± 3.2% (18.9 ± 11.5% bronchoprotection) after 2 weeks of salmeterol (P = 0.0001). The Arg16Gly polymorphisms were not associated with the LOB in response to salmeterol. FeNO values at baseline were significantly related to the LOB (r = 0.47; P = 0.01). Mean change was a 74 ± 13% LOB in subjects with FE(NO) levels greater than 50 ppb and a 7 ± 16% gain in bronchoprotection in those with FE(NO) levels less than 25 ppb (P = 0.01).

CONCLUSIONS

The LOB that occurs with chronic long-acting β2-agonists use is not affected by ADRB2 Arg16Gly polymorphisms. High FE(NO) was associated with marked LOB. Use of long-acting β2-agonists before achieving a reduction in FeNO may need to be avoided. Clinical trial registered with www.clinicaltrials.gov (NCT 00595361).

Updates on the COPD gene list

A genetic contribution to develop chronic obstructive pulmonary disease (COPD) is well established. However, the specific genes responsible for enhanced risk or host differences in susceptibility to smoke exposure remain poorly understood. The goal of this review is to provide a comprehensive literature overview on the genetics of COPD, highlight the most promising findings during the last few years, and ultimately provide an updated COPD gene list. Candidate gene studies on COPD and related phenotypes indexed in PubMed before January 5, 2012 are tabulated. An exhaustive list of publications for any given gene was looked for. This well-documented COPD candidate-gene list is expected to serve many purposes for future replication studies and meta-analyses as well as for reanalyzing collected genomic data in the field. In addition, this review summarizes recent genetic loci identified by genome-wide association studies on COPD, lung function, and related complications. Assembling resources, integrative genomic approaches, and large sample sizes of well-phenotyped subjects is part of the path forward to elucidate the genetic basis of this debilitating disease.

The role of vitamin D in asthma

Vitamin D metabolites are important immune-modulatory hormones and are able to suppress Th2-mediated allergic airway disease. Some genetic factors that may contribute to asthma are regulated by vitamin D, such as vitamin D receptor (VDR), human leukocyte antigen genes (HLA), human Toll-like receptors (TLR), matrix metalloproteinases (MMPs), a disintegrin and metalloprotein-33 (ADAM-33), and poly(ADP-ribosyl) polymerase- 1 (PARP-1). Vitamin D has also been implicated in asthma through its effects on the obesity, bacillus Calmettee Guérin (BCG) vaccination and high vitamin D level, vitamin D supplement, checkpoint protein kinase 1 (Chk1), plasminogen activator inhibitor-1 (PAI-1) and gamma delta T cells (gdT). Vitamin D plays a role in asthma and exerts its action through either genomic and/or non-genomic ways.

Relationship between polymorphisms in the 5' leader cistron, positions 16 and 27 of the adrenergic β2 receptor gene and asthma in a Han population from southwest China

BACKGROUND AND OBJECTIVE

Adrenergic β2 receptors (ADRB2) play an important role in regulating pulmonary function. Many previous studies have investigated possible associations between polymorphisms in the ADRB2 gene and asthma, but have yielded conflicting results. Furthermore, little is known regarding the possible role of the Arg19Cys polymorphism in susceptibility to asthma among Chinese.

METHODS

This case-control association study involved 238 patients with asthma and 265 healthy subjects from a Han population in southwest China. For all subjects, the 5' leader cistron Arg19Cys, Arg16Gly and Gln27Glu polymorphisms in the ADRB2 gene were characterized by direct sequencing. Genotype, allele and haplotype frequencies were determined. In addition, to evaluate the association between the ADRB2 polymorphisms and lung function, bronchodilator response to inhaled β2 agonists (400 µg of albuterol) was assessed in the asthmatic patients.

RESULTS

There were no significant differences in genotype or allele frequencies for the three ADRB2 polymorphisms between the two cohorts. The Arg19/Arg16/Gln27 haplotype was more frequent among asthmatic patients than control subjects (odds ratio 2.24, 95% confidence interval (CI): 1.05-4.73, P=0.04). Moreover, the Arg19/Cys19 genotype was associated with a lower FEV₁% (mean difference -4.5, 95% CI: -12.5 to 3.6, P=0.02) and FEV₁/FVC (mean difference 8.9, 95% CI: 8.5-9.4, P=0.01). The bronchodilator response to albuterol was also marginally lower in individuals who were homozygous for the Arg19 genotype (mean difference 4.2, 95% CI: 3.7-4.8, P=0.03).

CONCLUSIONS

The Arg19/Cys19 genotype was an independent risk factor for lower FEV₁% and FEV₁/FVC. Asthmatic patients with the Arg19/Arg19 genotype showed decreased responsiveness to albuterol. Furthermore, the Arg19/Arg16/Gln27 haplotype may contribute to increased susceptibility to asthma in the Chinese population.

The importance of environment on respiratory genotype/phenotype relationships in the Inuit

BACKGROUND

Genetic and environmental influences and their interactions are central to asthma pathogenesis. This study aimed to investigate the effects of different macro-environments on asthma genotype-phenotype associations in two geographically separated populations with common ancestry.

METHODS

To accomplish this, two unselected populations of Inuit were recruited, one living in Greenland (n = 618) and the other in Denmark (n = 739). Subjects were genotyped for CD14 C-159T, SCGB1A1 A38G, ADRB2 Arg16Gly and Gln27Glu. The resulting genetic data were analysed for relationships with asthma-related parameters including lung function, ever asthma, atopy, rhinitis and dermatitis.

RESULTS

The results showed contrasting magnitude and direction of genetic associations between the two geographically separate Inuit populations. In Greenland, the ADRB2 16Arg allele was associated with male-specific lower lung function, but in Denmark the same allele was associated with male-specific higher lung function. This allele was also associated with higher incidence of ever asthma in Denmark but not in Greenland. The SCGB1A1 38A allele was associated with lower rhinitis prevalence in Greenland but not in Denmark.

CONCLUSIONS

These associations suggest that environment interacts with candidate asthma genes to modulate asthma pathogenesis in the Inuit.

Polymorphism of the ADRB2 gene and response to inhaled beta- agonists in children with asthma: a meta-analysis

BACKGROUND

About 9% of children have asthma, corresponding to almost 6.8 million children in the USA and 1.1 million in the UK. Asthma exacerbations are the leading cause of pediatric emergency room visits and impose a large burden on the individual, family, and society. There is mounting evidence that therapeutic failure of inhaled beta-agonists is associated with polymorphisms of the beta(2)-adrenergic receptor gene (ADRB2); specifically, mutations leading to amino acid changes at positions 16 and 27, which alter down-regulation of the beta(2)-adrenergic receptor (beta(2)AR), induce resistance to the smooth-muscle relaxing effect of beta(2)-adrenergic agonists.

METHODS

We conducted a meta-analysis to examine the association between ADRB2 polymorphisms and the response to inhaled beta(2)-adrenergic agonists in children with asthma. We included all published studies until November 2008, in which asthmatic children underwent testing for acute bronchodilator response, defined as > or = 15% improvement in forced expiratory volume in 1 second (FEV(1)) and single nucleotide polymorphism (SNP) genotyping for positions 16 and/or 27 of the beta(2)AR. Individual and summary odds ratios were calculated using a random effects model.

RESULTS

We identified three case-control or family-based studies involving 960 asthmatic children (692 children with negative beta(2)-bronchodilator response, defined as < 15% improvement in FEV(1) and 268 children with positive bronchodilator response). We found a significant association between favorable therapeutic response to inhaled beta(2)-adrenergic agonists in asthmatic children and the Arg/Arg phenotype at position 16 of the beta(2)AR [OR = 1.77; 95% CI (1.01; 3.1); p = 0.029], compared with the Arg/Gly or Gly/Gly phenotypes. The beneficial effect of Arg at position 16 of the beta(2)AR was most pronounced in African-American asthmatic children [OR = 3.54; 95% CI (1.37, 9.13)]. There was no association between clinical response to beta(2)-agonists and polymorphism at amino acid position 27 of the beta(2)AR (OR = 1.04; 95% CI [0.76,1.42]).

CONCLUSIONS

Failure of bronchodilator response to inhaled beta-agonists in asthmatic children is associated with the Gly allele (Arg/Gly and Gly/Gly genotypes) at position 16 of the beta(2)-adrenergic receptor. Genetic typing for beta(2)AR polymorphism may help identify children with drug-resistant asthma.

Associations of beta2-adrenergic receptor genotypes and haplotypes with wheezing illness in Taiwanese schoolchildren

BACKGROUND

Increasing attention was focused on the beta2-adrenergic receptor gene (ADRB2), whose genetic variability has been implicated as a risk factor for asthma-related phenotypes. However, only a few studies reported the associations by utilizing haplotypic approaches. We therefore examined the relationship of childhood wheezing illness with polymorphisms at codons 16 and 27, and evaluated the influence of polymorphisms individually and in combination as haplotypes.

METHODS

We conducted a genetic case-control study comprising 215 wheezing children and 183 nonwheezing controls, all of whom were selected from 2524 fourth- to ninth-grade schoolchildren in southern Taiwan.

RESULTS

All participants were homozygous at the ADRB2 Thr164 locus. After controlling for possible confounders, ADRB2 Glu27 allele was significantly associated with wheezing illness in all genetic models, but the risks on Arg16Gly genotypes were inconclusive. Estimated frequencies for the three main hyplotypes were Arg16/Gln27 57.2%, Gly16/Gln27 35.3%, Gly16/Glu27 7.4% in wheezing children, and Arg16/Gln27 56.3%, Gly16/Gln27 32.2%, Gly16/Glu27 10.4% in controls. The protective effect of Gly16/Glu27 haplotype remained relative to all other ADRB2 haplotypes [adjusted relative risk (aRR) = 0.58; 95% confidence interval (CI) 0.35-0.97]. As compared with children without Gly16/Glu27 haplotype, those with Gly16/Glu27 haplotype had a significantly lower risk for wheezing illness (aRR = 0.56; 95% CI 0.33-0.99). The copy numbers of Gly16/Glu27 haplotype also showed a clear dose-response relationship on the decreased risks. No significant association was found with the prevalence of wheezing illness for other haplotypes.

CONCLUSION

We concluded that ADRB2 Glu27 allele and Gly16/Glu27 haplotype were significantly protective factors for wheezing illness in Taiwanese schoolchildren.

Polymorphisms of the beta2 adrenoreceptor gene in chronic obstructive pulmonary disease

BACKGROUND

The beta2-adrenergic receptors are cell surface receptors playing a central role in the pharmacological targeting asthma and chronic obstructive pulmonary disease [COPD]. Recent studies suggest that patients who are homozygous for one of the two important polymorphisms of the beta2-adrenergic receptor [ADRB2] gene at codon 16 (arginine to glycine) and 27 (glutamine to glutamate) may have a reduced response to ss2-agonists. Since smoking patients who are Gly16 homozygotes have an increased risk of airway obstruction we hypothesized that beta2-adrenoreceptor gene polymorphisms may be also a cofounder for COPD development and disease severity.

METHODS

We investigated 190 COPD patients and 172 healthy volunteers in a case-control study. DNA was isolated from whole blood and beta2-AR gene polymorphisms Arg/Gly16 and Gln/Glu27 were determined using allele-specific polymerase chain reaction [PCR].

RESULTS

In COPD patients with Gly/Gly16 was found more frequently than in healthy smokers [29.47% COPD versus 18.18% controls, p = 0.026]. All other gene polymorphisms of the ADRB2 gene at codon 16 were equally distributed between groups. ss2-adrenoreceptor gene polymorphisms were neither a cofounder for COPD exacerbations [>or= 3 hospitalizations within the last 3 years] nor for disease severity [FEV1 <or= 30% predicted].

CONCLUSION

Our study suggests that the Gly16 allele of the beta2-AR gene predisposes to COPD development but not for exacerbation rates and disease severity. In contrast, Gln/Glu27 polymorphism was irrelevant in our COPD cohort.

A new focus on assessing and treating asthma control in the African-American community: a call to action

Asthma continues to be a highly prevalent disease characterized by significant morbidity, unnecessary mortality, and substantial cost to the health care system. After decades of increasing prevalence, the number of current asthmatics in recent years has plateaued at approximately 22 million people in the United States. An additional 10 million Americans have a past history of asthma that is not active. The burden of asthma is higher among African Americans than in any other racial or ethnic group in America. The African-American community continues to experience a disproportional increase in asthma prevalence, morbidity, and mortality. The educational initiatives stemming from the newly revised National Heart Lung and Blood Institute (NHLBI) guidelines provide the opportunity to address the increased burden of asthma in the African American community. These new guidelines, released in August 2007, focus on asthma control as the primary goal of therapy, routine monitoring of asthma control, and use of asthma control assessments to direct treatment. The present review discusses the following: I. The impact of health disparities on outcomes of African Americans with asthma, II. The barriers that prevent asthmatic patients from achieving optimal control, III. The unique factors that challenge practitioners and patients in achieving optimal asthma control in the African American Community, IV. The impact of good asthma control and the need for patients and clinicians to assess asthma control in with a standardized assessment tool, and V. Strategic initiatives and the role of the End The Attacks NOW program in improving outcomes for African American patients with asthma.

Genetics of asthma: potential implications for reducing asthma disparities

Although genetic factors may partly explain the differences in asthma prevalence, morbidity, and mortality among ethnic groups in the United States, few studies of the genetics of asthma have included members of ethnic minority groups. Only one genome-wide linkage analysis of asthma and/or asthma-related phenotypes (conducted by the Collaborative Study on the Genetics of Asthma) has included any members of ethnic minority populations. The interpretation of the findings of genetic association studies of asthma in ethnic minority groups is complicated by reduced statistical power due to small sample sizes; the failure to correct for multiple comparisons; a lack of homogeneity of the populations studied with regard to area of residence, ancestral background, and/or country of origin; a lack of measurement of relevant environmental exposures; and (for case-control studies of genetic association) a lack of detection and control of potential population stratification. Genetic studies may improve our understanding of asthma and lead to new methods to prevent, diagnose, and treat this disease. Limited study of asthma genetics in ethnic minority populations is unacceptable, as it may prevent these groups from benefiting from future developments in asthma management and thus widen existing disparities in asthma care. Future genetic association studies of asthma among ethnic minorities in the United States should include large samples of populations that have been adequately defined with regard to area of residence, self-designated ancestry, and country of origin. These studies should also include an adequate assessment of potentially relevant environmental exposures and (for case-control association studies) population stratification.

G protein-coupled receptor pharmacogenetics

Common G protein-coupled receptor (GPCR) gene variants that encode receptor proteins with a distinct sequence may alter drug efficacy without always resulting in a disease phenotype. GPCR genetic loci harbor numerous variants, such as DNA insertions or deletions and single-nucleotide polymorphisms that alter GPCR expression and function, thereby contributing to interindividual differences in disease susceptibility/progression and drug responses. In this chapter, these pharmacogenetic phenomena are reviewed with respect to a limited sampling of GPCR systems, including the beta(2)-adrenergic receptors, the cysteinyl leukotriene receptors, and the calcium-sensing receptor. In each example, the nature of the disruption to receptor function that results from each variant is discussed with respect to the regulation of gene expression, expression on cell surface (affected by receptor trafficking, dimerization, desensitization/downregulation), or perturbation of receptor function (by altering ligand binding, G protein coupling, and receptor constitutive activity). Despite the breadth of pharmacogenetic knowledge available, assessment for genetic variants is only occasionally applied to drug development projects involving pharmacogenomics or to optimizing the clinical use of GPCR drugs. The continued effort by the basic science of pharmacogenetics may draw the attention of drug discovery projects and clinicians alike to the utility of personalized pharmacogenomics as a means to optimize novel GPCR drug targets.

Phenotypes of chronic obstructive pulmonary disease

The current clinical classification of smoking-related lung disease fails to take into account the heterogeneity of chronic obstructive pulmonary disease (COPD). With an increased understanding of pathophysiologic variation, COPD now clearly represents a spectrum of overlapping diseases with important extrapulmonary consequences. A "phenotype" describes the outward physical manifestations of a particular disease, and compromises anything that is part of the observable structure, function or behavior of an individual. Such phenotypic distinctions in COPD include: frequent exacerbator, pulmonary cachectic, rapid decliner, airways hyperresponsiveness, impaired exercise tolerance, and emphysema versus airways disease. These variable manifestations, each with unique prognostic, clinical and physiologic ramifications, represent distinct phenotypes within COPD. While all of these phenotypes have smoking as a common risk factor, the other risk factors that determine these phenotypes remain poorly understood. An individual smoker has variable expression of each phenotype and there is mounting evidence that COPD phenotypes have different clinical outcomes. These phenotypes can be broadly classified into one of three groups: clinical, physiologic and radiographic. This review presents the evidence for the spectrum of COPD phenotypes with a focused discussion on the pathophysiologic, epidemiologic and clinical significance of each subtype.

Pharmacogenetics of the beta 2-adrenergic receptor gene

Asthma is a complex genetic disease with multiple genetic and environmental determinants contributing to the observed variability in response to common antiasthma therapies. One focus of asthma pharmacogenetic research has been the beta2-adrenergic receptor gene (ADR beta 2) and its effect on individual responses to beta agonist therapy. Knowledge about the effects of ADR beta 2 variation on therapeutic responses is evolving and should not alter current Asthma Guideline approaches, which consist of the use of short-acting beta agonists (SABAs) for as-needed symptom-based therapy and the use of a regular long-acting beta agonist (LABA) in combination with inhaled corticosteroid therapy for those asthmatics whose symptoms are not controlled by inhaled corticosteroid alone. These approaches are based upon studies showing a consistent pharmacogenetic response to regular use of SABAs and less consistent findings in studies evaluating LABAs. The emerging pharmacogenetic studies are provocative and should lead to functional studies. Meanwhile, the conflicting data concerning LABAs may be caused by such factors as small sample sizes of study populations and differences in experimental design.

ADRB2 Arg16Gly polymorphism, lung function, and mortality: results from the Atherosclerosis Risk in Communities study

BACKGROUND

Growing evidence suggests that the Arg16Arg genotype of the beta-2 adrenergic receptor gene may be associated with adverse effects of beta-agonist therapy. We sought to examine the association of beta-agonist use and the Arg16Gly polymorphism with lung function and mortality among participants in the Atherosclerosis Risk in Communities study.

METHODOLOGY AND PRINCIPAL FINDINGS

We genotyped study participants and analyzed the association of the Arg16Gly polymorphism and beta-agonist use with lung function at baseline and clinical examination three years later and with all-cause mortality during 10 years of follow-up. Lung function was characterized by percent-predicted forced expiratory volume in 1 second. Associations were examined separately for blacks and whites. Black beta-agonist users with the Arg/Arg genotype had better lung function at baseline and at the second clinical visit than those with Arg/Gly and Gly/Gly genotypes. Adjusted mean percent-predicted FEV(1) was 21% higher in Arg/Arg subjects compared to Gly/Gly at baseline (p = 0.01) and 20% higher than Gly/Gly at visit 2 (p = 0.01). Arg/Gly subjects had adjusted percent-predicted FEV(1) 17% lower than Arg/Arg at baseline but were similar to Arg/Arg subjects at visit 2. Although black beta-agonist users with the Arg/Arg genotype appeared to have better crude survival rates, the association between genotype and all-cause mortality was inconclusive. We found no difference in lung function or mortality by genotype among blacks who did not use beta-agonists or among whites, regardless of beta-agonist use.

CONCLUSIONS

Black beta-agonist users with the ADRB2 Arg16Arg genotype had better lung function, and, possibly, better overall survival compared to black beta-agonist users with the Gly16Gly genotype. Our findings highlight the need for additional studies of sufficient size and statistical power to allow examination of outcomes among beta-agonist users of different races and genotypes.

G-protein-coupled receptors and asthma endophenotypes: the cysteinyl leukotriene system in perspective

Genetic variation in specific G-protein coupled receptors (GPCRs) is associated with a spectrum of respiratory disease predispositions and drug response phenotypes. Although certain GPCR gene variants can be disease-causing through the expression of inactive, overactive, or constitutively active receptor proteins, many more GPCR gene variants confer risk for potentially deleterious endophenotypes. Endophenotypes are traits, such as bronchiole hyperactivity, atopy, and aspirin intolerant asthma, which have a strong genetic component and are risk factors for a variety of more complex outcomes that may include disease states. GPCR genes implicated in asthma endophenotypes include variants of the cysteinyl leukotriene receptors (CYSLTR1 and CYSLTR2), and prostaglandin D2 receptors (PTGDR and CRTH2), thromboxane A2 receptor (TBXA2R), beta2-adrenergic receptor (ADRB2), chemokine receptor 5 (CCR5), and the G protein-coupled receptor associated with asthma (GPRA). This review of the contribution of variability in these genes places the contribution of the cysteinyl leukotriene system to respiratory endophenotypes in perspective. The genetic variant(s) of receptors that are associated with endophenotypes are discussed in the context of the extent to which they contribute to a disease phenotype or altered drug efficacy.

Beta2-agonists for asthma: the pediatric perspective

Inhaled beta-agonists are commonly prescribed for the treatment of wheezing disorders in infants and children. Despite this, there are concerns that these medications have potentially detrimental effects on lung health and symptoms. We will review the ontogeny of beta-agonist receptor and smooth muscle development from fetal life through infancy and childhood as well as the evidence supporting the clinical utility of beta-agonists in wheezing infants and asthmatic children. Finally, the potential detrimental effects of long- and short-acting beta-agonists in infants and children are discussed.

Association of haplotypes of beta2-adrenoceptor polymorphisms with lung function and airway responsiveness in a pediatric cohort

We evaluated the influence of haplotypes of beta(2)-adrenergic receptor (ADRB2) polymorphisms on lung function and airway responsiveness (AR) in a pediatric cohort recruited before birth and followed up to 11 years of age. The subjects (180) were the participants in a prospective study of lung function and AR. They have been assessed five times (at 1 month, 6 months, 12 months, 6 and 11 years of age) for lung function and AR. The two ADRB2 single nucleotide polymorphisms (SNPs): Arg16Gly and Gln27Glu were genotyped by PCR-RLFP and their haplotypes inferred using the program PHASE. An association between the haplotype arg16gln27 and the prevalence of positive AR was found at age 6 years (P = 0.009). The gly16gln27 haplotype was associated with higher FEV1 (P = 0.015) at age 6 and both higher FEV1 and FVC (P = 0.018 and P = 0.001, respectively) at age 11. In contrast, arg16gln27 was associated with both lower FEV1 and FVC (P = 0.028 and P = 0.011, respectively) at age 11. Children with the gly16gln27 haplotype were less likely to have asthma-ever or doctor-diagnosed asthma at age 11 (OR: 0.38; P = 0.019 and OR: 0.31; P = 0.041, respectively). In conclusion, haplotypes of beta(2)-adrenoceptor polymorphisms are associated with lung function, AR, and asthma susceptibility in childhood.

The role of novel genes in modifying airway responses in asthma

Major progress has been made during the past few years in developing a better understanding of the genetic basis of asthma, which has led to the identification of several chromosomal regions and loci showing linkage to and association with asthma and asthma-related phenotypes. Recent positional cloning approaches have also been informative in identifying several strong candidate genes for asthma. As another approach, association studies between candidate gene polymorphisms and asthma-related phenotypes have been conducted in many areas and replicated in different ethnic groups. These approaches need to be followed by validation processes to confirm their functional relevance in the pathophysiology of asthma. In this review, we describe several novel genes, including ADAM33, ADRB2, and eotaxin, that modify airway responsiveness in asthmatic patients.

Beta2-adrenergic receptor polymorphisms are associated with asthma and COPD in adults

The beta(2)-adrenergic receptor (beta(2)AR) is a transmembrane protein expressed by airway smooth muscle cells. In vitro studies have shown that polymorphisms at amino acid positions 16 and 27 alter receptor function. The aim of this study was to examine the associations between the beta ( 2 ) AR polymorphisms and risks of asthma, chronic obstructive pulmonary disease (COPD) and respiratory symptoms in a sample of adults. Participants were part of a cross-sectional population-based study of risk factors for respiratory disease. A total of 1,090 Caucasian participants completed a detailed respiratory questionnaire, spirometry, methacholine challenge and measurement of gas transfer. Genotyping for beta ( 2 ) AR polymorphisms at positions 16 and 27 was performed using the tetra-primer amplification refractory mutation system-polymerase chain reaction (ARMS-PCR) method. Haplotype frequencies for the two polymorphisms were estimated using the E-M algorithm. We found the Arg16 homozygotes had an increased risk of COPD (OR 5.13; 95% CI 1.40,18.8), asthma (2.44; 1.12,5.31) and symptoms of wheeze (1.84; 1.02,3.35). The Gln27 homozygotes had an increased risk of asthma (2.08; 1.05,4.13) and bronchial hyperreactivity (BHR) (1.92; 1.07,3.46). The Arg16/Gln27 haplotype was associated with asthma (1.63; 1.12,2.38) and COPD (2.91; 1.42,5.94). The Arg16/Gln27 beta(2)AR haplotype is important in COPD, asthma and BHR, and may be associated with more severe respiratory symptoms in middle-aged and older adults.

Sequence, haplotype, and association analysis of ADRbeta2 in a multiethnic asthma case-control study

RATIONALE

The comprehensive evaluation of gene variation, haplotype structure, and linkage disequilibrium is important in understanding the function of beta2-adrenergic receptor gene (ADRbeta2) on disease susceptibility, pulmonary function, and therapeutic responses in different ethnic groups with asthma.

OBJECTIVES

To identify ADRbeta2 polymorphisms and haplotype structure in white and African American subjects and to test for genotype and haplotype association with asthma phenotypes.

METHODS

A 5.3-kb region of ADRbeta2 was resequenced in 669 individuals from 429 whites and 240 African Americans. A total of 12 polymorphisms, representing an optimal haplotype tagging set, were genotyped in whites (338 patients and 326 control subjects) and African Americans (222 patients and 299 control subjects).

RESULTS

A total of 49 polymorphisms were identified, 21 of which are novel; 31 polymorphisms (frequency > 0.03) were used to identify 24 haplotypes (frequency > 0.01) and assess linkage disequilibrium. Association with ratio (FEV1/FVC)2 for single-nucleotide polymorphism +79 (p < 0.05) was observed in African Americans. Significant haplotype association for (FEV1/FVC)2 was also observed in African Americans.

CONCLUSIONS

There are additional genetic variants besides +46 (Gly16Arg) that are important in determining asthma phenotypes. These data suggest that the length of a poly-C repeat (+1269) in the 3' untranslated region of ADRbeta2 may influence lung function, and may be important in delineating variation in beta-agonist responses, especially in African Americans.

beta2-Adrenergic receptor polymorphisms and asthma in the North Indian population

INTRODUCTION

The beta(2)-adrenergic receptor (ADRB2) polymorphisms are known to be functionally relevant and disease modifying in subjects with asthma. However, the association of these polymorphisms with asthma remains to be established. Our objective is to investigate the association of the ADRB2 polymorphisms and haplotypes with asthma in North Indian subjects.

METHODS

A subset of 101 unrelated cases and 55 unrelated unaffected individuals were used for a case-control disease-association test.

RESULTS

Ten variable single nucleotide polymorphism (SNP) sites within a span of 2.193 kb were identified in the ADRB2 gene by the sequencing and genotyping of 351 bronchial asthma patients and healthy individuals. The distributions of genotype and allele frequencies for individual SNPs in the ADRB2 gene and ADRB2 haplotype frequencies were estimated in unrelated asthmatics and healthy individuals. No significant association was observed between ADRB2 genotypes and alleles with disease status after Bonferroni correction for multiple testing (reference p value = 0.0083). However, haplotype GGCTTTGCAA was found to be significantly associated with asthma (p = 0.021) in the studied population.

CONCLUSION

Our results suggest that there is likely to be a functional significance of the ADRB2 gene with asthma.

The C523A beta2 adrenergic receptor polymorphism associates with markers of asthma severity in African Americans

Our goal was to explore associations between ss2 adrenergic receptor polymorphisms and markers of asthma severity in African American and Caucasian patients with asthma. Polymorphisms at loci -1023, -654, -47, 46, 79, 491, and 523 were genotyped and haplotypes were imputed in 143 African Americans and 336 Caucasians. C523A genotype associated with percentage of African Americans (but not of Caucasians) having an asthma exacerbation: AA, AC, and CC genotypes were 17, 29, and 40%, respectively (p = 0.018). Symptom scores, pulmonary function, and rescue inhaler use paralleled exacerbation prevalence. We conclude the 523 A allele modifies asthma severity in African Americans.

Molecular-based haplotype analysis of the beta 2-adrenergic receptor gene (ADRB2) in Japanese asthmatic and non-asthmatic subjects

BACKGROUND

The beta2-adrenergic receptor gene (ADRB2) is a target molecule of beta2-agonists. Single nucleotide polymorphisms (SNPs) in the ADRB2 are related to the effectiveness of beta2-agonists. However, there are some discrepancies in the results of pharmacogenetic studies of ADRB2 among different ethnic groups. The aims of this study were to determine the ADRB2 haplotypes and diplotypes in Japanese asthmatic and non-asthmatic subjects and to examine their relation to asthma and to compare these results with previous studies done in other ethnic groups.

METHODS

Complete sequences for 3 kb promoter and 1.2 kb structural regions of ADRB2 were analyzed in 48 Japanese asthmatics and 100 controls, and haplotypes and diplotypes of SNPs were analyzed.

RESULTS

Fifteen SNPs including a novel one in -839 were observed. Allele frequencies for all SNPs were similar between asthmatics and controls. We also identified 42 haplotypes and 54 diplotypes of ADRB2 in a Japanese population. The frequencies were similar between the two groups. They were classified into 17 and 23 types, respectively, according to Drysdale's haplotype-organization system, and a significant ethnic difference was observed between the Japanese and Caucasian populations.

CONCLUSIONS

The frequencies of SNPs and ADBR2 haplotypes in Japanese are different from those in Caucasians and African Americans. These divergences might imply the need for independent pharmacogenetic studies for ADBR2 in each ethnic group.

Influence of beta2-adrenergic receptor genotype on airway function during exercise in healthy adults

BACKGROUND

In humans, beta(2)-adrenergic receptors (beta(2)ARs) influence airway tone. There are known functional polymorphisms of the beta(2)AR, such as substitution of glycine for arginine at codon 16. We sought to determine if this variation in genotype differentially influences airway function during exercise.

METHODS

Healthy subjects without asthma who were either homozygous for Arg16 (n = 16; mean age, 29 +/- 2 years [+/- SD]; mean maximum oxygen uptake [Vo(2)], 32 +/- 2 mL/kg/min) or the Gly16 allele (n = 26; mean age, 30 +/- 1 years; mean maximum Vo(2), 33 +/- 1 mL/kg/min) participated in the study. Baseline testing included spirometry and maximal symptom-limited exercise. On a separate day, an arterial cannula was placed to measure catecholamine levels. Subjects then performed exercise at two work levels (40% and 75% of peak work) for 9 min each and performed spirometry at 3-min intervals for assessment of airway function.

RESULTS

There were no statistically significant differences between groups in maximum Vo(2) or baseline spirometry (p > 0.05). With both light and heavy exercise, the groups had similar increases in the forced expiratory flow at 50% of vital capacity (FEF(50)). FEF(50) increased by 14 +/- 4% and 15 +/- 3% in arginine and glycine groups, respectively, by end exercise (p > 0.05). During recovery (5 min and 10 min after), the Gly16 homozygotes demonstrated persistent bronchodilation (10 min after FEF(50) = + 7 +/- 2% over pre-exercise) while the Arg16 subjects had a rapid return to baseline (10 min after FEF(50) = - 3 +/- 3%, p = 0.007 between groups). No differences were observed in the catecholamine responses between genotypes, although the increase in epinephrine in the arginine group tended to be higher (p = 0.07).

CONCLUSIONS

These data suggest that the Arg16Gly polymorphism of the beta(2)AR does not influence airway function during short-duration low- and high-intensity exercise. However, during recovery, the Arg16 genotype is associated with a reduced bronchodilation, possibly due to increased catecholamine desensitization.

Genetics and the Dutch Hypothesis

BACKGROUND

Increasingly, molecular genetic techniques are being used to improve our understanding of a number of common late onset complex disorders, such as hypertension, Alzheimer's disease and noninsulin dependent diabetes mellitus. Molecular genetic approaches have the potential to yield new information about disease pathogenesis that may be of great importance for the development of future treatments.

AIMS

This review discusses the evidence for a genetic contribution to the development of chronic obstructive pulmonary disease (COPD) and specifically focuses on the hypothesis that asthma and COPD share some pathogenic mechanisms as originally proposed in 1960 in a theory that has since become known as the Dutch Hypothesis. In particular we will review the evidence from molecular genetics, both in support of and against the theory.

Asthma in Hispanics

Hispanic individuals trace their ancestry to countries that were previously under Spanish rule, including Mexico, large parts of Central and South America, and some Caribbean islands. Most--but not all--Hispanics have variable proportions of European, Amerindian, and African ancestry. Hispanics are diverse with regard to many factors, including racial ancestry, country of origin, area of residence, socioeconomic status, education, and access to health care. Recent findings suggest that there is marked variation in the prevalence, morbidity, and mortality of asthma in Hispanics in the United States and in Hispanic America. The reasons for differences in asthma and asthma morbidity among and within Hispanic subgroups are poorly understood but are likely due to the interaction between yet-unidentified genetic variants and other factors, including environmental tobacco smoke exposure, obesity, allergen exposure, and availability of health care. Barriers to optimal management of asthma in Hispanics in the United States and in Hispanic America include inadequate access to health care, suboptimal use of antiinflammatory medications, and lack of reference values for spirometric measures of lung function in many subgroups (e.g., Puerto Ricans). Future studies of asthma in Hispanics should include large samples of subgroups that are well characterized with regard to self-reported ethnicity, country of origin, place of birth, area of residence, and indicators of socioeconomic status. Because Hispanics are disproportionately represented among the poor in the United States, implementation of adequate access to health care and social reforms (e.g., improving housing conditions) would likely have a major impact on reducing asthma morbidity in this population.

What is new with the beta2-agonists: issues in the management of asthma

OBJECTIVE

To review the more recent literature addressing the issue of whether beta2-agonists can worsen asthma and/or increase the risk of severe exacerbations and death from asthma.

DATA SOURCES

PubMed was searched (2001-December 2004), along with the Food and Drug Administration and Cochrane Library Web sites. In addition, the bibliographies of recent reviews of the subject were assessed.

STUDY SELECTION AND DATA EXTRACTION

Randomized clinical trials, retrospective and prospective cohort studies, and meta-analyses published in the past 3 years were reviewed. Studies assessing the potential for beta2-agonists to worsen outcomes in asthma as well as long-term studies assessing asthma outcomes that included an arm with regular administration of short- or long-acting inhaled beta2-agonists (LABAs) were selected. Worsening asthma was defined as a decline in lung function, an increase in bronchial hyperresponsiveness, exacerbations, or death. Studies older than 3 years selected from the bibliographies of the primary articles that addressed background perspective were also included where appropriate.

DATA SYNTHESIS

The studies fell into 3 primary categories with some overlap: those assessing toxicity of the S-enantiomer of albuterol, those evaluating the risk of specific genotypes regarding worsening asthma, and those assessing asthma outcomes with LABA therapy.

CONCLUSIONS

The current data on the use of beta2-agonists continue to support the national and international guidelines for the treatment of asthma. That is, short-acting inhaled beta2-agonists should only be used as needed for symptoms and prevention of exercise-induced bronchospasm, and LABAs should only be used regularly as adjunctive therapy with inhaled corticosteroids in patients whose asthma is not controlled with low to medium doses of the inhaled corticosteroid.

Beta2-adrenergic receptor gene polymorphisms and pregnancy outcome

AIMS

The association between alleles at two loci of the polymorphic beta2-adrenergic receptor (beta2AR) gene and pregnancy outcome was determined.

METHODS

In a case-control study, buccal swabs obtained from 159 mother-infant pairs after a preterm or term birth were analyzed by gene amplification and endonuclease digestion for polymorphisms at codons 16 and 27 of the beta2AR gene.

RESULTS

Homozygosity for allele A at codon 16 (Arg-16) occurred in 26 (20.5%) of 127 mothers with a term birth and in none of the mothers who had a spontaneous preterm birth (p=0.002). Conversely, 24 of 32 (75.0%) mothers with a spontaneous preterm birth, as compared to 58 of 127 (45.7%) mothers with term births, were Arg-16/ allele G (Gly-16) heterozygotes (p=0.003). There was no relation between pregnancy outcome and infant genotype at codon 16 or maternal or infant genotypes at codon 27. The alleles at codon 16 and 27 were in linkage disequilibrium and the combinations of Arg-16-Gln-27 homozygosity (p=0.04) and Arg-16/Gly-16-Gln homozygous (p=0.01) were associated with a decreased and increased rate of spontaneous preterm birth, respectively.

CONCLUSION

At codon 16 of the beta2-AR gene, maternal Arg-16 homozygosity protects against, and Gly-16 predisposes to spontaneous preterm birth.

Pharmacogenetic differences in response to albuterol between Puerto Ricans and Mexicans with asthma

BACKGROUND

In the United States, Puerto Ricans and Mexicans have the highest and lowest asthma prevalence, morbidity, and mortality, respectively. Ethnic-specific differences in the response to drug treatment may contribute to differences in disease outcomes. Genetic variants at the beta(2)-adrenergic receptor (beta(2)AR) may modify asthma severity and albuterol responsiveness. We tested the association of beta(2)AR genotypes with asthma severity and bronchodilator response to albuterol in Puerto Ricans and Mexicans with asthma.

METHODS

We used both family-based and cross-sectional tests of association with 8 beta(2)AR single nucleotide polymorphisms in 684 Puerto Rican and Mexican families. Regression analyses were used to determine the interaction between genotype, asthma severity, and bronchodilator drug responsiveness.

RESULTS

Among Puerto Ricans with asthma, the arginine (Arg) 16 allele was associated with greater bronchodilator response using both family-based and cross-sectional tests (p = 0.00001-0.01). We found a strong interaction of baseline FEV(1) with the Arg16Glycine (Gly) polymorphism in predicting bronchodilator response. Among Puerto Ricans with asthma with baseline FEV(1) < 80% of predicted, but not in those with FEV(1) > 80%, there was a very strong association between the Arg16 genotype and greater bronchodilator responsiveness. No association was observed between Arg16Gly genotypes and drug responsiveness among Mexicans with asthma.

CONCLUSIONS

Ethnic-specific pharmacogenetic differences exist between Arg16Gly genotypes, asthma severity, and bronchodilator response in Puerto Ricans and Mexicans with asthma. These findings underscore the need for additional research on racial/ethnic differences in asthma morbidity and drug responsiveness.

beta2 adrenoceptor Arg16Gly polymorphism, airway responsiveness, lung function and asthma in infants and children

BACKGROUND

We have previously reported a relationship between increased airway responsiveness (AR) in infancy and reduced childhood lung function.

OBJECTIVE

The current study aimed to determine whether the Arg16Gly polymorphism of the beta2 adrenoceptor (beta2AR) gene was important to this relationship.

METHODS

A cohort that initially numbered 253 individuals underwent assessments of AR and lung function aged 1 month, 6 and 11 years; genotyping for polymorphisms of the beta(2)AR was performed.

RESULTS

At 1 month of age, the genotype homozygous Arg16 (n=24) was associated with a mean increase in log dose-response slope (AR) of 0.27 [95% confidence interval (CI) 0.07, 0.49] compared with the genotype homozygous Gly16 (n=58), P=0.01. At 11 years of age, the genotype homozygous Arg16 (n=35) was associated with a mean reduction in the percentage of forced expiratory volume in 1 s of 5.3% [95% CI 0.3, 10.2] compared with the genotype homozygous Gly16 (n=65), P=0.03. There was no association between the Arg16Gly polymorphism and atopy or diagnosed asthma. However, nine of 69 individuals with the genotype homozygous Gly16 were admitted to hospital with asthma compared with five out of 111 individuals with the remaining genotypes (P<0.05).

CONCLUSION

The Arg16Gly polymorphism may be important to the association between increased AR in infancy and reduced lung function in childhood and may also be a determinant of asthma severity in children but not asthma per se.

Beta 2-adrenergic receptor polymorphisms and haplotypes are associated with airways hyperresponsiveness among nonsmoking men

STUDY OBJECTIVE

To investigate the relationship of common single nucleotide polymorphisms (SNPs) of the beta(2)-adrenergic receptor (AR) gene at codons 16 and 27, and the intermediate phenotype of airways hyperresponsiveness.

DESIGN

A case-control study in 543 white men (152 case patients and 391 control subjects), who were nested in an ongoing longitudinal cohort.

SETTING

Subjects were selected from the Normative Aging Study, an ongoing longitudinal cohort of healthy aging.

PARTICIPANTS

Case patients were defined as those having a positive response to methacholine challenge testing. Control subjects were selected among those who did not have a diagnosis of asthma and who had no response to methacholine.

RESULTS

There was a trend for an association of the Arg16 SNP genotype with airways hyperresponsiveness (odds ratio, 1.25; 95% confidence interval, 0.96 to 1.64 [in an additive model]). In stratified analyses, the effect of the Arg16 variant was seen mainly among nonsmokers. Smokers had increased risks for airway hyperresponsiveness regardless of genotype at either SNP. Using a program to estimate haplotype frequencies, three common haplotypes were identified. Adjusting for age, baseline FEV(1), serum IgE level, and smoking status, the Gly16/Gln27 haplotype was negatively associated with airways hyperresponsiveness in the full complement of case patients and control subjects (score statistic, - 2.43; p = 0.02). The effect of the beta(2)-AR haplotypes was much stronger among lifelong nonsmokers, among whom the Gly16/Gln27 haplotype remained negatively associated with airways hyperresponsiveness (score statistic, - 3.114; p = 0.002), whereas the Arg16/Gln27 haplotype was positively associated with airways hyperresponsiveness (score statistic, 3.142; p = 0.002). No effects were seen among ever-smokers.

CONCLUSIONS

In this cohort of middle-aged to older white men, beta(2)-AR polymorphisms were associated with airways hyperresponsiveness, particularly among lifelong nonsmokers. Our results illustrate an instance in which greater power is obtained by performing haplotype analyses as opposed to single SNP analysis.

Symptoms, lung function, and beta2-adrenoceptor polymorphisms in a birth cohort followed for 10 years

As little is known about the natural history of bronchial responsiveness and the development of wheezing symptoms in early childhood, a cohort of children at risk of allergy, whose lung function and bronchial responsiveness had been measured in the neonatal period, was followed prospectively for 10 (SD, 0.8) years in order to determine the role of neonatal measurements on wheezing history and later lung function. A potential role for beta-2 adrenoceptor (beta2AR) polymorphisms in these relationships was also sought as a secondary objective. Of the original 73 children, wheezing history was available in 65 (89%), and 49 (67%) attended the laboratory for physiological measurements and genotyping of beta2AR. Wheezing was categorized as occurring 1) only before the fourth birthday, 2) after the fourth birthday, or 3) never. No relation was seen between neonatal and later lung function. However, neonatal bronchial responsiveness predicted subsequent FEV1 (P = 0.03). Increased neonatal bronchial responsiveness was associated with transient wheeze <4 years but not with later wheeze. Neonatal V'maxFRC was reduced in those possessing Gln27 or Arg16 alleles, but there was no effect of beta2AR polymorphisms on FEV1 at 10 years. Wheeze after 4 years of age was typical of classical asthma, as it was strongly related to atopy and bronchial responsiveness at age 10. In conclusion, we confirmed the association of neonatal bronchial responsiveness with both early wheezing and later lung function. We also showed an influence of polymorphisms at both aa16 and aa27 on neonatal lung function. Wheezing beyond 4 years, typical of classical asthma, was unrelated to early measurements of lung function or bronchial responsiveness.

Association between beta2-adrenoceptor polymorphisms and asthma diagnosis among Mexican adults

BACKGROUND

Recent studies demonstrate that genetic variations in the human beta(2)-adrenergic receptor (beta(2)AR) structure at codons 16 and 27 alter receptor function in vitro and are associated with asthma severity and airway hyperresponsiveness but have not been linked to asthma diagnosis. The nature of the relation in a more homogeneous population is uncertain.

OBJECTIVE

We determined frequencies of these polymorphisms to explore the association between beta(2)AR haplotypes and asthma diagnosis and phenotype.

METHODS

This is a population-based, case-control study that involves a total sample of 907 unrelated Mexican Mestizos. Genotyping at beta(2)AR was identified by polymerase chain reaction-restriction fragment length polymorphism analysis. Multivariate logistic regression analysis was used to estimate the odds ratio (OR) of the association between beta(2)AR haplotype status and asthma diagnosis.

RESULTS

A significant inverse association was found between subjects with Glu27 allele (OR, 0.5; 95% CI, 0.4 to 0.7) and Gly16-Glu27 alleles (OR, 0.5; 95% CI, 0.3 to 0.8) and asthma. Sex differences in this association were explored, given the complex relation between sex and asthma. Among men, a positive association was present between the "Gly16 allele without Glu27" (OR, 2.9; 95% CI, 1.26 to 6.8) and asthma. In contrast, a lower risk of asthma was found among women Gly16-Glu27 alleles (OR, 0.3; 95% CI, 0.2 to 0.6). Nocturnal asthma was associated with the Gly16 allele (OR, 1.8; 95% CI, 1.3 to 2.6).

CONCLUSIONS

Variation in the beta(2)AR gene is associated in the pathogenesis of asthma and acts as a disease modifier in nocturnal asthma.

Genetics of susceptibility to human helminth infection

Recent studies have shown that host genetics is an important determinant of the intensity of infection and morbidity due to human helminths. Epidemiological studies of a number of parasite species have shown that the intensity of infection (worm burden) is a heritable phenotype. The proportion of variance in human worm burden explained by genetic effects varies from 0.21 to 0.44. Human genome scans have identified a locus responsible for controlling Schistosoma mansoni infection intensity on chromosome 5q31-q33, and loci controlling Ascaris lumbricoides intensity on chromosomes 1 and 13, although the genes involved have not yet been identified. There is also evidence for genetic control of pathology due to S. mansoni, and linkage has been reported to a region containing the gene for the interferon-gamma receptor 1 subunit. There is some evidence for genetic control of filarial infection, though little information on filarial disease. Association studies have provided evidence for major histocompatibility complex control of pathology in schistosomiasis and onchocerciasis. Recent candidate gene studies suggest a role of other immune response genes in controlling helminth infection and pathology, but require replication. Identification of the genetic loci involved may be important in the understanding of helminth epidemiology and the mechanisms of resistance and pathology.

Family-based association analysis of beta2-adrenergic receptor polymorphisms in the childhood asthma management program

BACKGROUND

Beta2-adrenergic receptor (B2AR) polymorphisms have been associated with a variety of asthma-related phenotypes, but association results have been inconsistent across different studies.

OBJECTIVE

We sought to apply family-based association methods to individual single nucleotide polymorphisms (SNPs) and haplotypes of SNPs in B2AR to define the relationship of these genetic variants to asthma-related phenotypes.

METHODS

DNA samples were obtained from 707 Childhood Asthma Management Program participants, representing 650 sibships, as well as their parents. Genotyping was performed at 8 B2AR SNPs. Qualitative asthma-related phenotypes were analyzed with single SNPs and haplotypes by using TRANSMIT; quantitative asthma-related phenotypes were analyzed with the Family-Based Association Test.

RESULTS

Several SNPs, including SNP -654 and SNP +46, demonstrated significant associations (P <.05) to postbronchodilator FEV1 as both a qualitative (<80% of predicted value) and quantitative phenotype. Quantitative phenotypic association analysis demonstrated significant evidence for association of SNP +523 with bronchodilator responsiveness expressed as a percentage of baseline FEV1 (P =.012) or a percentage of predicted FEV1 (P =.008). Similar evidence for association between the +523 SNP and qualitative bronchodilator responsiveness phenotypes was also found. Analysis of haplotypes supported an association of B2AR variants with spirometric values and bronchodilator responsiveness.

CONCLUSION

B2AR variants are associated with spirometric values and bronchodilator responsiveness, but different regions of the gene provide evidence for association with these phenotypes.

Association studies for asthma and atopic diseases: a comprehensive review of the literature

Hundreds of genetic association studies on asthma-related phenotypes have been conducted in different populations. To date, variants in 64 genes have been reported to be associated with asthma or related traits in at least one study. Of these, 33 associations were replicated in a second study, 9 associations were not replicated either in a second study or a second sample in the same study, and 22 associations were reported in just a single published study. These results suggest the potential for a great amount of heterogeneity underlying asthma. However, many of these studies are methodologically limited and their interpretation hampered by small sample sizes.

Beta-adrenoceptor polymorphisms

There can be no doubt that beta(1)-, beta(2)- and beta(3)-adrenoceptor genes have genetic polymorphisms. Two single nucleotide polymorphisms have been described for the beta(1)- (Ser49Gly; Gly389Arg), three for the beta(2)- (Arg16Gly; Gln27Glu; Thr164Ile) and one for the beta(3)-adrenoceptor subtype (Trp64Arg) that might be of functional importance. The possibility that changes in expression or properties of the beta-adrenoceptors due to single nucleotide polymorphisms might have phenotypic consequences influencing their cardiovascular or metabolic function or may contribute to the pathophysiology of several disorders like hypertension, congestive heart failure, asthma or obesity is an idea that has attracted much interest during the last 10 years. At present, it appears that these beta-adrenoceptor polymorphisms are very likely not disease-causing genes, but might be risk factors, might modify disease and/or might influence progression of disease. The aim of this review is to provide an overview of the functional consequences of such beta-adrenoceptor polymorphisms in vitro, ex vivo and in vivo.

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 in the beta2 adrenergic receptor and bronchodilator response, bronchial hyperresponsiveness, and rate of decline in lung function in smokers

BACKGROUND

Non-specific bronchial hyperresponsiveness (NSBH) is a known predictor of accelerated rate of decline in lung function in smokers. Polymorphisms of the beta(2) adrenergic receptor (ADRB2) have previously been associated with NSBH and bronchodilator response (BDR) in asthmatics. Based on these associations, we hypothesised that ADRB2 polymorphisms would be associated with NSBH and BDR as well as an accelerated rate of decline in lung function among smokers.

METHODS

The prevalence of two ADRB2 polymorphisms, Arg16-->Gly and Gln27-->Glu, was examined in 587 smokers chosen from the NHLBI Lung Health Study for having the fastest (n=282) and slowest (n=305) 5 year rate of decline in forced expiratory volume in 1 second (FEV(1); mean DeltaFEV(1) -4.14 and +1.08% predicted/year, respectively).

RESULTS

Contrary to our hypothesis, no ADRB2 allele or haplotype was associated with NSBH, BDR, or rate of decline in lung function. However, there was a significant negative association between heterozygosity at position 27 and a fast decline in lung function (adjusted odds ratio 0.56, 95% CI 0.40 to 0.78, p=0.0007).

CONCLUSIONS

Heterozygosity at position 27 may be protective against an accelerated rate of decline in lung function. The polymorphism at position 16 does not contribute to the rate of decline in lung function, measures of NSBH, or BDR in smokers.