determining whether heterogeneity in COPD definitions, including varying degrees of severity and case ascertainment, differential effects of genetic variants in disease versus lung function in the general population, or Type 1 or Type 2 error could account for these discrepancies. The number of loci achieving genome-wide significance described here for COPD is few compared to other complex diseases102,103, and the markers described here account for a very small fraction of the estimated heritability18. For unknown reasons, the number of discovered loci confirmed by GWAS for any given sample size can vary widely104,105.
