Statistically significant associations have been recently noted between several SNP in the region of MUC5AC and MUC5B and the respiratory diseases familial interstitial pneumonia and idiopathic pulmonary fibrosis.8 These authors claim that a single SNP about 3 kb upstream from the start of transcription of MUC5B is causal, because it is associated with increased expression and the rarer allele is four times more frequent in patients than controls. Here, MUC5B is linked to idiopathic pulmonary fibrosis.