CFTR and cystic fibrosis: In cystic fibrosis (CF), mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene result in defective mucociliary clearance and, as a consequence, lead to the production of thick and sticky bronchial mucus, which facilitates the entrapment of airborne viruses, bacteria and fungal spores and provides a suitable environment for the growth of these microorganisms.