CFTR and cystic fibrosis: We have observed that the CF basic defect is determined via KRT8 whereby the phylogenetically older KRT8 haplotype 2211 is dominant for the manifestation of CFTR mediated residual chloride secretion and also recognized consistently as the benign modifier allele that is associated with a milder clinical phenotype among concordant CF sibpairs (Table 2, Figure 2).