Among mucin gene cluster (MUC6, MUC2, MUC5AC, and MUC5B) on chromosome 11q15.5, MUC5B is the most predominant in the normal distal airway epithelium and is widely associated with sporadic IPF and familial interstitial pneumonia (9, 25–27). Here, MUC5AC is linked to idiopathic pulmonary fibrosis.