A promoter variant rs7115457 is associated with diffuse pan bronchiolitis (Kamio et al., 2005), while another MUC5B promoter polymorphism, rs35705950, is the strongest risk factor, genetic or otherwise, accounting for 30–35% risk of developing Idiopathic pulmonary fibrosis (IPF), a disease that was previously considered idiopathic. The gene discussed is MUC5B; the disease is pulmonary fibrosis.