METTL3 and chronic obstructive pulmonary disease: The expressions of IGF2BP3, FTO, METTL3 and YTHDC2, which have the significant associations with some key genes (such as BCL2A1, GPX2, AKR1B10, ALDH3A1, CABYR, CYP4F3, EGF, UCHL1, CYP1A1, CYP1B1 and MUCL1) enriched in the signalling pathway and biological processes that promote the development progression of COPD, are highly correlated with the occurrence of COPD.