While Zhang et al. did not include COPD patients in their analyses, Cai et al. [18] and Smith et al. [41] analyzed several datasets of gene expression of COPD and control small and large airway epithelium samples, concluding that ever-smoking was the main factor associated with high ACE2 levels; however, the effect of COPD was not consistent across datasets. This evidence concerns the gene ACE2 and chronic obstructive pulmonary disease.