Cystic fibrosis is the most common life-shortening autosomal recessive disorder in the white population, affecting approximately 30,000 persons in the United States.¹ It is caused by mutations in a single gene on the long arm of chromosome 7 that encodes the cystic fibrosis transmembrane conductance regulator (CFTR) (Figure 1).² CFTR has multiple functions involving fluid balance across epithelial cells. It acts as a chloride channel activated by cyclic adenosine monophosphate (cAMP)³ and may stimulate other chloride channels⁴ and inhibit sodium absorption by epithelial sodium channels.⁵

Mutations in the CFTR gene result in defective chloride transport in the epithelial cells in . . .