Similarly to asthma-suffering individuals, also COPD patients displayed increased MMP-9 serum levels, which moreover correlated negatively with the Tiffeneau–Pinelli index (FEV1/FVC ratio) (Brajer et al. 2008; Erlewyn-Lajeunesse et al. 2008). This evidence concerns the gene MMP9 and chronic obstructive pulmonary disease.