Over the past decade, we discovered a gain-of-function [6] promoter variant in MUC5B (rs35705950, G; T) that is the dominant risk factor for IPF (OR = 5.45; 95% CI = 4.91–6.06; p = 9.60 × 10−295) [7], present in >50% of affected patients and accounting for at least 30% of the risk of disease [8,9]. This evidence concerns the gene MUC5B and idiopathic pulmonary fibrosis.