mRNA expression of SPDEF, MUC5AC, MUC1, MUC20, MUC4, MUC13, MUC2, MUC16 and SCNN1A was higher, whereas expression of SCNN1G was lower in COPD and current smokers compared to ex and never‐smokers (Figure 2E, Table S3 in the Supporting Information). This evidence concerns the gene MUC4 and chronic obstructive pulmonary disease.