Correlation of sweat chloride concentration with genotypes in cystic fibrosis patients in Saguenay Lac-Saint-Jean, Quebec, Canada

Objectives: Saguenay Lac-Saint-Jean, a geographically isolated region of northeastern Quebec has a high incidence of cystic fibrosis (CF) and three mutations only account for 94% of the CF chromosomes. The objective of the present study was to determine whether different mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene had different effects upon the sweat chloride concentration. Design and Methods: The sweat chloride concentration of 114 patients was measured by quantitative pilocarpine iontophoresis. Results: CF patients carrying the A455E mutation, usually associated with pancreatic sufficiency, had lower sweat chloride concentrations than those carrying mutations associated with pancreatic insufficiency (Delta F508 and 621 + 1G-->T). Conclusions: Our results confirm that mutations resulting in a reduction of the chloride current at the apical membrane of epithelial cells induce lower sweat chloride values. However, there are differences in the chloride current between genotypes, even if they are composed of mutations apparently having the same functional effect.