Interestingly, the SPDEF binding site located in the ~3 kb upstream region of MUC5B contained rs35705950, a SNP that was previously reported as associated with idiopathic pulmonary fibrosis, in which the lung hypersecretes MUC5B (Fig 8B; Seibold et al, 2011). Here, MUC5B is linked to idiopathic pulmonary fibrosis.