The National Emphysema Treatment Trial (NETT) cases have FEV1≤45% predicted and emphysema on chest CT scan [20], [21]. Thus, NETT cases have COPD severity of GOLD Stage 3 or greater. All NETT Genetics Ancillary Study subjects are former smokers; only white subjects are included in this analysis. The Normative Aging Study (NAS) is a cohort study of initially healthy men followed by the Boston VA [22]. To define a control group for comparison to NETT cases, we selected Caucasian subjects meeting the following criteria: FEV1>80% predicted, FEV1/FVC>90% predicted, at least 10 pack-years of smoking, and an adequate DNA sample [23]. Genomewide SNP genotyping has been performed in the NETT-NAS study (366 cases, 414 controls) using the Illumina 610-Quad BeadChip [11].
