Quantitative real-time PCR (qRT-PCR) analysis of samples from smokers with or without COPD confirmed that relative to normal smokers without COPD, the expression of TBX3, TBX5, HDAC6, SIRT1, SIRT5, is suppressed in severe cases of COPD (Figure 2). This evidence concerns the gene TBX5 and chronic obstructive pulmonary disease.