MUC5B and cystic fibrosis: In addition, the expression level of MUC5B changes with the development of conditions, including chronic obstructive pulmonary disease, cystic fibrosis, and idiopathic pulmonary fibrosis.[16–18] A genome-wide association study showed that SNP rs868903 of the MUC5B promoter was strongly associated with pulmonary fibrosis.[19] However, it remains unclear whether MUC5B is associated with the risk of onset of CWP.