CFTR and cystic fibrosis: The major difference in the genotype – phenotype correlations of 'leaky' splice mutations between human individuals and the CF/1-CftrTgH(neoim)Hgu and CF/3-CftrTgH(neoim)Hgu mouse models resides in the fact that the manifestation of disease in humans is attenuated with increasing amounts of correctly spliced CFTR mRNA whereas the inbreeding of the mice selected for tissue specific modulation of lowered wild-type Cftr mRNA levels.