The group of COPD patients and NLF controls were primarily compared in order to identify geneticvariants and interactions of genetic and environmental factors implicated in the pathogenesis of COPD, while VBD controls were introduced for additional testing of gene-gene interaction since no carrier of the double risk genotype, eNOS TT and ACE DD, was detected by using NLF controls. Here, ACE is linked to chronic obstructive pulmonary disease.