Intermediate-range sweat chloride concentration and Pseudomonas bronchitis. A cystic fibrosis variant with preservation of exocrine pancreatic function.

We studied the clinical and laboratory characteristics of seven patients with sweat 
chloride concentration consistently between 40 and 60 mEq/liter. Each has chronic 
Pseudomonas bronchitis, and all lack digestive symptoms. Laboratory findings indicate the 
preservation of exocrine pancreatic function. The patients include two of five 
children in one family and two of four in another. In 
a third family, one of five siblings has an intermediate sweat 
chloride concentration, but another has a typical fibrosis value (105 mEq/liter). 
One patient died of respiratory failure; results of an autopsy showed 
bronchiolectasis typical of cystic fibrosis, but minimal pancreatic changes. The data 
suggest a genetic basis for this variant of cystic fibrosis. These 
patients may be homozygous for a portion of a closely linked 
multigene cystic fibrosis locus or may have modifier genes that ameliorate 
the pancreatic and sweat lesions. 