Controls had normal spirometry with a history of cigarette smoking. For the analysis of ‘severe’ COPD, cases were limited to those with GOLD 3 and 4 disease (severe and very severe, post-bronchodilator FEV1 < 50% predicted). Baseline characteristics of each of the genome-wide cohorts are shown in Table 1. Logistic regression was performed within each cohort and racial / ethnic group adjusting for age, pack-years of smoking, and ancestry-based principal components using plink (v1•07)37, as previously described7,12. Fixed-effects meta-analysis was performed using METAL (version 2010-08-01)38. Heterogeneity was reported as both I239 using the meta package in R (v2•3•0) (www.r-project.org) and P-values for Cochrane's Q. Markers were included for analysis if they passed genotyping or imputation quality control (as appropriate) in all genome-wide cohorts. Regional association plots were created using LocusZoom40, using the 1000 Genomes EUR reference data for linkage disequilibrium (LD) calculations.
