Although more than 1,400 mutations are known in CFTR (http://www.genet.sickkids.on.ca/cftr), approximately 90% of CF patients carry the allele with deletion of the codon for phenylalanine at position 508 [6], which is located in the first nucleotide-binding domain (NBD1) (Figure 1). The gene discussed is CFTR; the disease is cystic fibrosis.