In our recent epigenome-wide associated study analysis, we found that ACO patients had hypermethylated phosphodiesterase 9A (PDE9A; +30,088 CpG site)/zinc finger and SCAN domain containing 31 (ZNF323; ZSCAN31;·−296 CpG site), and hypomethylated septin 8 (SEPT8; −47 CpG site) genes as compared with either pure COPD patients or healthy non-smokers. Here, PDE9A is linked to chronic obstructive pulmonary disease.