All of the following comments about cystic fibrosis (CF) are true except:

CF an autosomal recessive disorder. Approximately 50% will survive to the age of 25. In 1989, the CF gene was found to be located on the long arm of chromosome 7, The CF protein is called the cystic fibrosis transmembrane regulatory protein (CFTR). The most common mutation is the three-base deletion removing a phenylalanine residue at position 508 of CFTR, called the F508 mutation. The basic defect is due to a defect in chloride permeability, which can result in the accumulation of mucus and can lead to stasis and obstruction. Both the upper and lower airways can be involved, and they can lead to frequent bronchial infections predominated early by Staphylococcus aureus and Hemophilus influenzae and in late disease by Pseudomonas aeruginosa. The diagnosis is usually made by the sweat test performed by quantitative pilocarpine iontophoresis. CF diagnosis is confirmed by an elevated sweat chloride concentration greater than 60 mEq/L.