Interest in investigating TGFβ1 as a potential modifier of CF pulmonary disease stemmed from both its biologic plausibility, and its identification as a modifier of asthma and chronic obstructive pulmonary disease (COPD) (Pulleyn et al., 2001; Celedon et al., 2004; Silverman et al., 2004; Wu et al., 2004). This evidence concerns the gene TGFB1 and lung disorder.