ADRB2 p.Thr164Ile association with hospitalization depends upon asthma severity
Authors: Lynn D. Condreay, Mathias N. Chiano, Li Li, Elizabeth Harris, Dana J. Fraser, Deborah A. Meyers, Eugene R. Bleecker, Courtney Crim, David Stempel, Steven W. Yancey, Soumitra Ghosh
Journal: Journal of Allergy and Clinical Immunology (2019)

The identification of robust genetic variants predictive of asthma exacerbation could impact patient management. Results testing genetic effects of p.Gly16Arg of the β2-adrenoceptor gene (ADRB2), the “target gene” for short-acting β-agonists and long-acting β-agonists (LABAs) on response to short-acting β-agonists and LABAs, have been inconsistent.1Israel E. Drazen J.M. Liggett S.B. Boushey H.A. Cherniack R.M. Chinchilli B.M. et al.The effect of polymorphisms of the beta(2)-adrenergic receptor on the response to regular use of albuterol in asthma.Am J Respir Crit Care Med. 2000; 162: 75-80Crossref PubMed Scopus (505) Google Scholar, 2Israel E. Chinchilli V.M. Ford J.G. Boushey H.A. Cherniack R. Craig T.J. et al.Use of regularly scheduled albuterol treatment in asthma: genotype-stratified, randomized, placebo-controlled cross-over trial.Lancet. 2004; 364: 1505-1512Abstract Full Text Full Text PDF PubMed Scopus (549) Google Scholar, 3Wechsler M.E. Lehman E. Lazarus S.C. Lemanske Jr., R.F. Boushey H.A. Deykin A. et al.Beta-adrenergic receptor polymorphisms and response to salmeterol.Am J Respir Crit Care Med. 2006; 173: 519-526Crossref PubMed Scopus (284) Google Scholar, 4Bleecker E.R. Yancey S.W. Baitinger L.A. Edwards L.D. Klotsman M. Anderson W.H. et al.Salmeterol response is not affected by beta2-adrenergic receptor genotype in subjects with persistent asthma.J Allergy Clin Immunol. 2006; 118: 809-816Abstract Full Text Full Text PDF PubMed Scopus (141) Google Scholar, 5Bleecker E.R. Nelson H.S. Kraft M. Corren J. Meyers D.A. Yancey S.W. et al.Beta2-receptor polymorphisms in patients receiving salmeterol with or without fluticasone propionate.Am J Respir Crit Care Med. 2010; 181: 676-687Crossref PubMed Scopus (101) Google Scholar More recently, Ortega et al6Ortega V.E. Hawkins G.A. Moore W.C. Hastie A.T. Ampleford E.J. Busse W.W. et al.Effect of rare variants in ADRB2 on risk of severe exacerbations and symptom control during long-acting β agonist treatment in a multiethnic asthma population: a genetic study.Lancet Respir Med. 2014; 2: 204-213Abstract Full Text Full Text PDF PubMed Scopus (87) Google Scholar reported that the low-frequency ADRB2 variant p.Thr164Ile (rs1800888, C>T) increased exacerbation risk (including hospitalization) in non-Hispanic white patients receiving LABAs (odds ratio [OR], 4.48; 95% CI, 1.40-9.96; P = .01). Two recent studies in adult (N = 11,679) and pediatric (N = 6,208) patients with asthma7Stempel D.A. Raphiou I.H. Kral K.M. Yeakey A.M. Emmett A.H. Prazma C.M. et al.Serious asthma events with fluticasone plus salmeterol versus fluticasone alone.N Engl J Med. 2016; 374: 1822-1830Crossref PubMed Scopus (117) Google Scholar, 8Stempel D.A. Szefler S.J. Pedersen S. Zeiger R.S. Yeakey A.M. Lee L.A. et al.N Engl J Med. 2016; 375: 840-849Crossref PubMed Scopus (87) Google Scholar reported that subjects receiving a LABA-containing regimen were at no higher risk for severe asthma outcomes than were subjects who received inhaled corticosteroid treatment alone, suggesting that LABA-containing treatment alone does not predict serious asthma events. To better understand potential genetic effects for the ADRB2 p.Thr164Ile variant on asthma exacerbation risk, this post hoc analysis tested the association between this variant and hospitalization for asthma exacerbation and the related end point of exacerbation rate in 2037 subjects with moderate-to-severe asthma across 6 clinical trials (see this article's Online Repository at www.jacionline.org) and in 6912 patients with asthma from the UK Biobank.9Allen N.E. Sudlow C. Peakman T. Collins R. UK Biobank.Sci Transl Med. 2014; 6: 224ed4Crossref PubMed Scopus (222) Google Scholar Because Ortega et al6Ortega V.E. Hawkins G.A. Moore W.C. Hastie A.T. Ampleford E.J. Busse W.W. et al.Effect of rare variants in ADRB2 on risk of severe exacerbations and symptom control during long-acting β agonist treatment in a multiethnic asthma population: a genetic study.Lancet Respir Med. 2014; 2: 204-213Abstract Full Text Full Text PDF PubMed Scopus (87) Google Scholar reported that the minor allele of p.Thr164Ile was associated with hospitalization for asthma exacerbation exclusively in LABA-treated patients with severe asthma, all subjects in this study received LABA-containing regimens. Subjects from the clinical trials were divided into subgroups in whom exacerbation risk differed by clinical characterization (Table I): Subgroup I (patients with moderate-to-severe asthma from ADA109055 [NCT00452699], ADA109057 [NCT00452348], and HZA106837 [NCT01086384]), II (patients with severe asthma from MEA201722 [IDEAL; NCT02293265]), and III (patients with severe asthma having an eosinophilic phenotype based on blood eosinophil counts from MEA112997 [Dose Ranging Efficacy and Safety with Mepolizumab in Severe Asthma, DREAM; NCT01000506] and MEA115588 [Mepolizumab as Adjunctive Therapy in Patients with Severe Asthma, MENSA; NCT01691521]). Subjects from the UK Biobank included “all-comer” asthmatic subjects, hence included subjects with less severe asthma.Table IDemographic and disease characteristics across all trials' subjects included in these analysesCharacteristicSubgroup I:Least severe asthmaSubgroup II:Severe asthmaSubgroup III:Severe eosinophilic asthma with history of multiple exacerbationsMultisample comparison for subgroups I (study subsets ADA and HZA), II, and IIIUK Biobank asthma sampleStudy subset ADA ADA109055 ADA109057Study subset HZA HZA106837Study MEA201722Combined study subsetStudy subset MEA112997Study subset MEA115588P value*P value ≤ 5 × 10−4 was used to declare that a characteristic in at least 1 study was distinct from other studies.Clinical practice sample†Clinical practice sample = patients with asthma in clinical practice taking LABA-containing treatment to control their asthma. Characteristics in the UK Biobank that were similar, but not identical, to those in the clinical trial subgroups. No. of exacerbations at baseline = no. of exacerbations reported in the medical history for the year before the study. Asthma exacerbation hospitalization at baseline = asthma exacerbation hospitalization reported in the medical history for the year before the study; 591 of 6912 (8.5%) patients with asthma on LABA-containing treatment in the UK Biobank had an exacerbation resulting in hospitalization (mean, 2.2 ± 3.53).N1216105187884513376912Age (y), mean ± SD41.92 ± 14.3943.21 ± 16.6750.22 ± 15.5949.56 ± 12.0848.56 ± 11.1150.88 ± 13.179.57 × 10−2258.85 ± 7.56Sex: female, n (%)65 (54)395 (65)327 (63)473 (60)282 (63)191 (57)7.06 × 10−24044 (59)Body mass index (kg/m2), mean ± SDNA27.53 ± 6.0929.73 ± 7.2928.02 ± 5.7228.14 ± 5.8227.86 ± 5.599.96 × 10−928.80 ± 5.75Weight (kg), mean ± SDNA76.09 ± 18.4083.85 ± 22.5878.52 ± 17.4978.91 ± 17.3177.99 ± 17.758.62 × 10−1180.04 ± 17.35Eosinophil level at baseline (GI/L), mean ± SDNA0.31 ± 0.290.28 ± 0.270.40 ± 0.390.39 ± 0.390.41 ± 0.405.47 × 10−110.29 ± 0.057Eosinophil baseline category (GI/L), n (%) 0-≤0.15NA190 (31)185 (36)191 (24)115 (25)76 (23)1 (<1) 0.15-≤0.3NA187 (31)160 (31)212 (27)124 (27)88 (26)2.59 × 10−124520 (65) 0.3-≤0.5NA128 (21)91 (18)168 (21)95 (21)73 (22)2321 (34) >0.5NA92 (15)69 (13)212 (27)117 (26)95 (28)39 (<1)FEV1 % of predicted at baseline, mean ± SD71.55 ± 12.3371.74 ± 10.6369.27 ± 21.5058.58 ± 16.0258.71 ± 15.6258.42 ± 16.561.29 × 10−5683.01 ± 21.29FVC (mL) at baseline, mean ± SDNANA3154.88 ± 1043.942988.98 ± 914.783027.36 ± 920.782937.63 ± 905.522.52 × 10−33345 ± 944.41Exacerbation number at baseline, mean ± SDNANA1.37 ± 1.653.68 ± 3.073.72 ± 3.413.62 ± 2.571.02 × 10−50Not applicableExacerbation number during treatment, mean ± SD0.34 ± 0.650.19 ± 0.50Not relevant0.98 ± 1.401.20 ± 1.590.67 ± 1.043.24 × 10−40NAAsthma exacerbations hospitalization at baseline (yes), n (%)NANA50 (9.7)182 (23)114 (25)68 (20)3.87 × 10−10Not applicableAsthma exacerbation hospitalization during treatment (yes), n (%)NANANA49 (6)39 (9)10 (3)NANAFEV1 reversibility‡Percent reversibility = 100 × (postbronchodilator FEV1 – prebronchodilator FEV1)/(prebronchodilator FEV1). Absolute reversibility = postbronchodilator FEV1 – prebronchodilator FEV1. (%), mean ± SD21.52 ± 9.8024.41 ± 12.7312.36 ± 16.0726.44 ± 22.1125.48 ± 21.1527.72 ± 23.301.74 × 10−44NADuration of asthma (y), mean ± SDNA14.07 ± 12.8725.37 ± 17.0119.22 ± 14.0518.04 ± 13.3620.79 ± 14.179.18 × 10−36NADuration of asthma categorical (y), n (%) 0-≤12 (12)48 (8)7 (1)15 (2)6 (1)9 (3)NA 1-≤512 (10)128 (21)51 (10)120 (15)89 (20)31 (9)NA 5-≤1013 (11)150 (25)65 (13)138 (18)86 (19)52 (15)1.70 × 10−32NA 10-≤1522 (18)87 (14)61 (12)115 (15)58 (13)57 (17)NA >1572 (60)197 (32)332 (64)400 (51)212 (47)188 (56)NArs1800888, n (%) C_C117 (97)592 (97)506 (98)771 (98)443 (98)328 (97)6685 (97) C_T4 (3)18 (3)12 (2)15 (2)7 (2)8 (2)8.61 × 10−01225 (3) T_T0 (0)0 (0)0 (0)2 (<1)1 (<1)1 (<1)2 (<1)FVC, Forced vital capacity; NA, not available.∗ P value ≤ 5 × 10−4 was used to declare that a characteristic in at least 1 study was distinct from other studies.† Clinical practice sample = patients with asthma in clinical practice taking LABA-containing treatment to control their asthma. Characteristics in the UK Biobank that were similar, but not identical, to those in the clinical trial subgroups. No. of exacerbations at baseline = no. of exacerbations reported in the medical history for the year before the study. Asthma exacerbation hospitalization at baseline = asthma exacerbation hospitalization reported in the medical history for the year before the study; 591 of 6912 (8.5%) patients with asthma on LABA-containing treatment in the UK Biobank had an exacerbation resulting in hospitalization (mean, 2.2 ± 3.53).‡ Percent reversibility = 100 × (postbronchodilator FEV1 – prebronchodilator FEV1)/(prebronchodilator FEV1). Absolute reversibility = postbronchodilator FEV1 – prebronchodilator FEV1. Open table in a new tab FVC, Forced vital capacity; NA, not available. Basic demographic information was similar for subjects in subgroups I, II, and III. However, there were marked differences in clinical characterization of asthma for the 3 subgroups (Table I), justifying the need to analyze subject-level data in relatively homogeneous subgroups to account for these differences and to meta-analyze summary statistics. Some of the differences reflect differences in inclusion criteria for enrollment into the source trials. For example, the number of asthma exacerbations reported in the 12 months before study initiation was lower for subjects included into subgroup II than into subgroup III. This reflects the requirement in the inclusion criteria of a history of 2 or more asthma exacerbations in the 12 months before study only for subjects in subgroup III. Details on asthma exacerbation criteria by study characteristics are in Table E1 in this article's Online Repository at www.jacionline.org. UK Biobank subjects were generally older and had the least severe asthma overall. Because of significant differences in trial designs, disease severity (measured by FEV1 percent predicted, oral corticosteroid use, frequency of asthma exacerbations, proportion of subjects with exacerbations requiring hospitalization), and patient characteristics included in this investigation, association between the ADRB2 p.Thr164Ile variant and asthma exacerbations was evaluated, first in relatively homogeneous subgroups, and then meta-analyzed across the subgroups (see detailed methods in this article's Methods section in the Online Repository at www.jacionline.org). End points tested included rate of asthma exacerbations (Fig 1, A) and hospitalization risk for asthma exacerbations (Fig 1, B). Too few subjects in subgroup I, with more moderate disease, experienced asthma exacerbation-related hospitalizations to warrant testing for genetic association. There was no statistically significant effect of the ADRB2 p.Thr164Ile variant on asthma exacerbation rate, in any subgroup or across all subgroups (Fig 1, A). For subgroups II and III, with the latter composed of subjects with higher numbers of eosinophils and more severe disease, a larger proportion of subjects experienced more exacerbations resulting in hospitalizations; 9.7% (50 of 518) for subgroup II and 23% (182 of 788) for subgroup III. Carriage of the T allele was significantly associated with asthma exacerbation-related hospitalizations in subgroup II (OR, 2.46; 95% CI, 1.18-5.12; P = .02) but not in subgroup III (OR, 1.15; 95% CI, 0.39-3.38; P = .80). However, the effect was statistically significant when meta-analyzed across both groups (OR, 1.94; 95% CI, 1.06-3.55; P = .03) (see Fig 1, B). In the UK Biobank samples, which included a broad range of subjects with asthma in clinical practice, 8.6% (591 of 6912) of patients who reported taking LABA maintenance treatments experienced asthma exacerbations that resulted in hospitalization. In this sample, the ADRB2 p.Thr164Ile variant was not associated with risk for hospitalization for asthma exacerbation (OR, 1.12; 95% CI, 0.72-1.78; P = .59). Combining information across subgroups II and III and UK Biobank samples was not statistically significant (OR, 1.37; 95% CI, 0.96-1.97; P = .09; see Fig 1, B). There was no evidence of significant heterogeneity in p.Thr164Ile variant effect estimates between the analysis subgroups (P = .57). The ADRB2 p.Thr164Ile variant was not associated with hospitalizations for asthma exacerbations when tested in all patients with asthma regardless of LABA use (OR, 1.16; 95% CI, 0.88-1.53; P = .31). This study investigated the impact of the ADRB2 2 p.Thr164Ile variant on exacerbation risk in a large sample of patients with asthma with genetic and exacerbation data (n = 8949). Given the large numbers of patients with asthma, ranging from mild to severe disease (n = 8949), this analysis had more than 80% power to detect a genetic effect (minor allele frequency, MAF = 0.018) with an OR of more than 1.8. With differences in clinical manifestations, such as asthma exacerbation rate, disease severity and airflow limitation, duration of disease, and blood eosinophil levels, the genetic analysis subpopulations that comprise this analysis likely represent different subtypes of asthma. No robust, and therefore no compelling, association was found between the ADRB2 p.Thr164Ile variant and either rate of exacerbation or hospitalization for asthma exacerbations across all patient subgroups. Although the p.Thr164Ile variant provided moderate association evidence (P < .05) in analysis of patients with severe asthma (subgroup II), no similar association effects were observed in patients either with less severe asthma (subgroup I) or in more eosinophilic patients (subgroup III). Similarly, no genetic association with asthma exacerbations was found in patients from the UK Biobank. While meta-analyzing hospitalizations for asthma exacerbation across the 2 more severe asthma subgroups, II and III, remained moderately significant (P = .03), overall meta-analysis with the UK Biobank samples was only suggestive of a genetic effect but not statistically significant (P = .09). Therefore, without additional independent study samples matching the asthma subpopulation described in subgroup II, it is not possible to test whether the effect identified represents a false positive or whether the effect is unique to a subtype of asthma. In conclusion, in the LABA-treated severe asthma subpopulation most consistent with the disease population described in Ortega et al,6Ortega V.E. Hawkins G.A. Moore W.C. Hastie A.T. Ampleford E.J. Busse W.W. et al.Effect of rare variants in ADRB2 on risk of severe exacerbations and symptom control during long-acting β agonist treatment in a multiethnic asthma population: a genetic study.Lancet Respir Med. 2014; 2: 204-213Abstract Full Text Full Text PDF PubMed Scopus (87) Google Scholar the ADRB2 p.Thr164Ile variant was associated with hospitalization for asthma-related exacerbations but no evidence of a similar genetic effect was found in patients with milder asthma. It was not possible to determine whether risk differed by LABA treatment in this study. We thank Michael Mosteller, Jonas Daugherty, Ibrahim Raphiou, Pamela St Jean, Joshua Hoffman, and Philip Appleby for consultations in planning and review and statistical analysis assistance. This research has been conducted using data from multiple GlaxoSmithKline-sponsored trials and the UK Biobank Resource under Application Number 26041. We thank all patients who take part in our trials and participants in the UK Biobank study. Subgroup I, the first analyses subgroup (n = 731), included 121 subjects from ADA109055 (NCT00452699) and ADA109057 (NCT00452348) and 610 subjects from HZA106837 (NCT01086384). Subjects in this subgroup had the least severe asthma with less impairment of airflow (baseline FEV1, percent of predicted) and fewer exacerbations during the study (Table I). Subjects enrolled in ADA109055 and ADA109057 were required to have a diagnosis of persistent asthma for at least 6 months (as defined by the American Thoracic Society) with documented use of a low to medium dose of an inhaled corticosteroid (ICS) or combination with a controller medication for at least 4 weeks before screening, with a prebronchodilator FEV1 at screening of 50% to 85% predicted normal value. Subjects were excluded from the studies if they experienced a worsening of asthma symptoms requiring an emergency room visit, hospitalization, or oral corticosteroid (OCS)/parenteral corticosteroid within 4 weeks of screening or were deemed to have had an episode of life-threatening worsening of asthma within 12 months before screening. The 121 subjects from ADA109055 and ADA109057 received fluticasone propionate/salmeterol. Subjects enrolled in HZA106837 were required to have a diagnosis of asthma (as defined by National Heart, Lung, and Blood Institute) for at least 1 year before the study and to be using ICS or ICS/LABA for at least 12 weeks before the study with a stable dose for at least 4 weeks before the study. All subjects enrolled in HZA106837 had FEV1 of 50% to 90% predicted normal value at screening and were required to have a history of 1 or more asthma exacerbation in the 12 months before the study that required treatment with oral/systemic corticosteroid, emergency room visit, or hospitalization. Subjects were excluded if a history of life-threatening asthma was documented within the preceding 5 years. The 610 non-Hispanic white subjects from study HZA106837 received the ICS/LABA combination of fluticasone furoate/vilanterol. Data for analyses were collected during the clinical trial conduct period. DNA samples from ADA109055 and ADA109057 were genotyped using the Illumina HumanOmni 1-Quad array, conducted by Expression Analysis (Durham, NC), and samples from HZA106837 were genotyped using the Affymetrix Axiom Biobank Genotyping Array with custom content v2, conducted by BioStorage Technologies/Bioprocessing Solutions Alliance (Piscataway, NJ). For this subgroup, analysis was performed in HZA106837 and in the pooled ADA109055/ADA109057 subjects separately, and then meta-analyzed using the summary statistics. The second analysis subgroup, subgroup II, included 518 subjects from study MEA201722 (IDEAL; NCT02293265), which recruited those with severe asthma, as defined by the European Respiratory Society/American Thoracic Society Guidelines for Severe Asthma. This was an epidemiology study and, as such, did not have an active treatment component. Clinical and treatment data included for this analysis was based on 12-month medical history information collected at baseline, before patient enrollment. All subjects were required to be treated with high-dose ICS plus an additional controller. LABA-treatment information was, therefore, not uniformly controlled for subjects included in this subgroup because active treatment was not part of the study design. DNA samples from this study were genotyped using the Affymetrix Axiom Biobank Genotyping Array with custom content v2, conducted by BioStorage Technologies/Bioprocessing Solutions Alliance. Subgroup III, the third analyses subgroup (n = 788), included 451 subjects from study MEA112997 (DREAM; NCT01000506) and 337 subjects from study MEA115588 (MENSA; NCT01691521). All subjects were required to have documented controller medication of LABA, leukotriene receptor antagonist, or theophylline in the 12 months before the study and to have persistent airflow obstruction (prebronchodilator FEV1 <80% predicted for adults; FEV1 <90% or FEV1/forced vital capacity <0.8 for subjects aged 12-17 years, using the Third National Health and Nutrition Examination Survey predictive equations) at screening or peak flow diurnal variability of more than 20% on 3 or more days during a run-in period. All subjects enrolled in MEA112997 and MEA115588 were older than 12 years and met the inclusion criteria of having severe asthma (defined in the European Respiratory Society/American Thoracic Society guidelines), having a confirmed history of 2 or more exacerbations requiring OCS or systemic corticosteroid in the year before the study despite high-dose ICS and additional controller medication, and having an eosinophilic phenotype based on blood eosinophil counts, which help to predict response to mepolizumab treatment. For both MEA112997 and MEA115588, information on LABA use as well as on asthma exacerbations was derived from medical records for the year before enrollment and during the study treatment period. The sample during the study treatment period included a set of 224 subjects, MEA112997 (n = 113) and MEA115588 (n = 111), who were enrolled but randomized to placebo and who had complete information on LABA use and exacerbation history. DNA samples from MEA112997 were genotyped using the OmniExpress Exome Bead Chip by Expression Analysis (Morrisville, NC). MEA115588 was genotyped using the Affymetrix Axiom Genotyping Array with GlaxoSmithKline custom content v2 by BioStorage Technologies/Bioprocessing Solutions Alliance. Bidirectional Sanger sequencing was also performed by BioStorage Technologies to confirm the ADRB2 p.Thr164Ile genotype in both MEA112997 and MEA115588. To assess effects of asthma exacerbation in a broader sample, 6912 patients with asthma were evaluated from the UK Biobank, a large UK collection of approximately 500,000 subjects, aged 40 to 69 years at enrollment, recruited between 2006 and 2010 with extensive clinical measures and linkage to electronic health records including hospitalizations. Information on hospitalizations for asthma exacerbations was derived from linked hospital episode statistic records. The UK Biobank is not a representative sampling of the general UK population, with a healthy selection bias, but integrating hospital episode statistic data and other data sources has proven to be reliably generalizable of disease-exposure relationships in the United Kingdom (PMCID PMC5860371). To enroll in the UK Biobank, subjects were not required to have asthma. However, all subjects in the UK Biobank collection who were included in this investigation were diagnosed with asthma and FEV1 was assessed at baseline (although lung function is not a dichotomous variable defining asthma severity). Therefore, this patient collection likely forms a subject collection with milder asthma than that of the patients with moderate to severe asthma in the clinical trial subgroups. Genotyping for the UK Biobank samples was performed as previously described (bioRxiv 166298; doi: https://doi.org/10.1101/166298). LABA use was derived from self-reported medical history information collected at enrollment. Demographic and clinical variables were summarized by mean and SD for continuous variables and proportions for categorical variables. Testing for equality of sample means or proportions across the analyses subgroups was performed using ANOVA methods, and, where appropriate, categorical variables were converted to ordinal variables. Variables with large numbers of categories or missing data, for example, country, were not tested. Because of the large number of variables and contrasts of interests examined (∼100), differences between subgroups or contrasts were considered as statistically significant at the P less than or equal to 5 × 10−4 level. Statistical analyses and data set preparations were conducted using SAS (SAS/STAT PROC GENMOD), Version 9.2 of the SAS System for Windows (2008, SAS Institute Inc, Cary, NC) and the R analysis software (http://www.R-project.org). Departure from Hardy-Weinberg equilibrium was tested using Fisher exact test, and calculation of genetic principal components (PCs) using genome-wide variants was carried out using SNP & Variation Suite v8.3.4 (Golden Helix, Inc, Bozeman, Mont, www.goldenhelix.com). Baseline characteristics were evaluated and, if significantly correlated with the outcome, were included in the model when testing for genetic association with the ADRB2 variant. Because all patients included for analyses in subgroup I were derived from trials that specifically enrolled patients with less severe disease, asthma exacerbation events requiring hospitalization in these studies were very limited (eg, 12/1625 intent-to-treat subjects receiving fluticasone propionate/salmeterol in the ADA studies or fluticasone furoate/vilanterol in the HZA106837 study, combined); association between the ADRB2 variant and hospitalizations for asthma exacerbations was not tested in this subgroup. Logistic regression was used to test for genetic association with hospitalization for asthma exacerbations in the subjects with more severe asthma in subgroups II and III, with the following baseline covariates maintained in the model: genetic PCs 1 to 5, FEV1, percent of predicted FEV1, heart rate, country of enrollment as well as a dummy variable representing the source trial. Regression analysis assuming a negative binomial model was used to test for genetic association and the number of asthma exacerbations (time on treatment was included as an offset variable in subgroup I). No offset variable was considered for subgroups II and III (data derived for a fixed 12-month period before study initiation). Genetic PCs 1 to 5, as well as relevant clinical and demographic variables measured at baseline, were maintained as covariates in the model including age, FEV1 percent of predicted, FEV1/forced vital capacity, OCS use, heart rate, country, and study. For the ADRB2 p.Thr164Ile risk allele variant (T), tests were 2-sided, with P value of .05 considered statistically significant. Similarly, for the UK Biobank, logistic regression was used to test for genetic association with hospitalization for asthma exacerbation status versus no hospitalization. Age at recruitment, sex, chip, and body mass index were maintained as covariates in the regression model. Unlike in clinical trial subgroups with limited numbers of highly selected and characterized subjects with asthma, genetic PCs 1 to 10 were included in the regression models for the large UK Biobank cohort (n = 6912) to account for any residual genetic admixture in the data. Fixed-effect, inverse variance meta-analyses were used to combine results from the various subgroups. All subjects included in these analyses are white of European ancestry. The ADBR2 p.Thr164Ile variant was present in all genotyping panels and was directly typed. Genetic data quality control (QC) and genome-wide PCs were computed within each analysis subgroup. There are, however, several limitations to our present study. It was not possible to test whether the effect of the p.Thr164Ile variant was dependent on LABA treatment because there was no severe asthma patient collection available that was not treated with a LABA. Furthermore, the choice of trials and patients included for analyses in this study may be inherently biased. For example, several trials were evaluated for inclusion in this analysis many of which had low hospitalization rates for asthma (<2/100 non-Hispanic white subjects with asthma, in Centers for Disease Control and Prevention data), which makes it generally difficult to recruit enough subjects with hospitalizations for asthma exacerbations. Invariably, data had to be extracted from multiple trials, where the underlying severity of disease differed, which was dictated by specific inclusion and exclusion criteria applied to each of the clinical trials. In this context, ascertainment bias will inevitably be introduced and caution will need to be taken interpreting or generalizing results from these data. Although lack of compliance is less likely to be an issue in the clinical trial sample because subjects were required to maintain 80% to 120% adherence per the dose-counter, disease severity and lack of compliance may generally make a post hoc pharmacogenetic study, as in this case using medical history, less reliable. For example, subjects in subgroups II and III and the UK Biobank used retrospective health records to characterize exacerbation history, and in the UK Biobank, LABA use was derived from self-reported medication records, which may be biased. Medication information from primary care (general practitioner) records is not currently available for the UK Biobank.Table E1Asthma exacerbation criteria by studyStudyExacerbation criteriaADA109055 and ADA1090957Exacerbations were defined as the requirement of treatment with an oral or parenteral corticosteroid or an unscheduled urgent care (eg, unscheduled clinic visit, MD office visit, emergency room visit, and hospitalization) for acute asthma symptoms requiring intervention.HZA106837A severe asthma exacerbation is defined as deterioration of asthma requiring the use of systemic corticosteroids (tablets, suspension, or injection) for at least 3 d or an in-patient hospitalization or emergency department visit due to asthma that required systemic corticosteroids.MEA201722Exacerbations were defined as requiring treatment with systemic corticosteroids or an asthma-related emergency department visit or hospitalization.MEA122997Exacerbations were defined by a worsening of asthma requiring the use of oral/systemic corticosteroids and/or hospitalization and/or emergency department visit. For subjects on maintenance OCSs, an exacerbation was defined as the use of oral/systemic corticosteroids at least double the existing maintenance dose for at least 3 d. Protocol-defined exacerbations were based on objective assessments of asthma.MEA115588Exacerbations must require treatment with systemic corticosteroids (intramuscular, intravenous, or oral) despite the use of high-dose ICS. For subjects receiving maintenance corticosteroids, the corticosteroid treatment for the exacerbation must have been a 2-fold increase or greater in the dose. Open table in a new tab