MUC5B and idiopathic pulmonary fibrosis: Although the gain-of-function MUC5B promoter variant is the dominant risk factor for this disease (11), accounting for at least 50% of the genetic risk of developing IPF (5), multiple biological mechanisms involving dysregulation of host defense, cell adhesion, telomere biology, mitotic spindle assembly, surfactant protein biology, and GTPase activity are implicated in the risk of developing IPF.