SOX9, another Wnt target gene, was also confirmed to be down-regulated in the small airway epithelium of healthy smokers and smokers with COPD compared to healthy nonsmokers (3.9-fold for smokers vs nonsmokers and 3.2-fold for smokers with COPD vs nonsmokers, both p<0.01). This evidence concerns the gene SOX9 and chronic obstructive pulmonary disease.