A variant promoter of this gene, rs35705950, is reported to be a risk factor for pulmonary fibrosis; furthermore, in pulmonary fibrosis, Muc5b has been shown to be expressed not only in the conducting airways but also in epithelial cells lining honeycomb cysts, and its expression level in the mouse bronchoalveolar epithelium is associated with impaired mucociliary clearance and the extent and persistence of bleomycin-induced pulmonary fibrosis [44, 45]. This evidence concerns the gene MUC5B and pulmonary fibrosis.