There are ‘two residual function’ CF mouse models, Cftrtm/Hgu and Cftrtm/Bay that show 90 and 40% survival respectively, but also have 10 and 2% of wild type (WT) Cftr mRNA present that would contribute to their higher survival rates (O'Neal et al., 1993; Wilke et al., 2011). Here, CFTR is linked to cystic fibrosis.