 Cystic Fibrosis CF is an autosomal recessive systemic disorder of exocrine glands and secretory epithelia. The disease results from mutations in the cystic fibrosis transmembrane conductance regulator CFTR gene which cause a variety of abnormalities. CFTR is absent or dysfunctional in cystic fibrosis. Most of the defects in CFTR result in abnormal chloride ion transport and abnormally viscous mucus. Nasal epithelial CFTR function will be assessed by the NPD procedure. 