SFTPA2 and idiopathic pulmonary fibrosis: The MAF of the MUC5B promoter polymorphism was approximately 30% in our IPF cohort which is similar to previous reports.12, 38 Since this frequency is similar in patients with IPF with and without other candidate gene mutations, this polymorphism is not associated with increased risk for disease in association with the exonic mutations in ABCA3, SFTPA2, SFTPC or TERT.