MUC5B and idiopathic pulmonary fibrosis: While smoking (3) and the inhalation of silica (4) are well-known environmental factors that cause idiopathic pulmonary fibrosis (IPF), several genetic variants for surfactant protein-C, surfactant protein-A2, telomerase reverse transcriptase, telomerase RNA component, and MUC5B have been identified as factors associated with IPF or familial interstitial pulmonary fibrosis (5–8).