In humans, the CLCA1/CLCA4 gene locus acts as a modifier of rectal anion conductance of CF patients and allelic variants of both CLCA1 and CLCA4 are associated with the severity of intestinal phenotype or the capability to express residual chloride secretion in the colon epithelium, respectively [1,3,4]. This evidence concerns the gene CLCA4 and cystic fibrosis.