Serum TGF-β levels have been found to be higher in COPD patients than in controls, whereas the highest levels were found in patients with Global Initiative for Chronic Obstructive Lung Disease (GOLD) stage 4 according to spirometry, suggesting a stage-dependent association between systemic TGF-β levels and lung function [5]. This evidence concerns the gene TGFB1 and chronic obstructive pulmonary disease.