Controls were divided into smoker and non-smoker groups, but similar MMP-12 protein levels were found in both groups (3.2 ± 1.1 and 3.5 ± 1.5 ng/ml, respectively; p = 0.45), with significantly lower values compared to patients with COPD (p < 0.0001 for both subgroups). This evidence concerns the gene MMP12 and chronic obstructive pulmonary disease.