CFTR Genotype and Maximal Exercise Capacity in Cystic Fibrosis: A Cross-sectional Study.

RATIONALE Cystic fibrosis transmembrane conductance regulator (CFTR) is expressed in human skeletal muscle cells. Variations of CFTR dysfunction among patients with CF may present an important determinant of aerobic exercise capacity in CF. Previous studies on the relationship between CFTR genotype and aerobic exercise capacity are scarce and contradictory. OBJECTIVES This study was designed to explore factors influencing aerobic exercise capacity, expressed as peak oxygen consumption (VO2peak) with a specific focus on CFTR genotype in children and adults with CF. METHODS In an international, multicenter cross-sectional study we collected data on CFTR genotype and cardiopulmonary exercise tests (CPET) in patients with CF eight years and older. CFTR mutations were classified into functional classes I-V. RESULTS The final analysis included 726 patients (45% females, age 8 to 61 years, FEV1 16 to 123 % predicted) from 17 CF centers in North America, Europe, Australia and Asia whom all had both valid maximal CPET and complete CFTR genotype data. Overall, patients exhibited exercise intolerance (VO2peak, 77.3±19.1 % predicted), but values were comparable among different CFTR classes. Using linear regression analysis adjusted for relevant confounders, lung function and body mass index, but not CFTR genotype were the main predictors of VO2peak. CONCLUSIONS We conclude that lung disease severity and reduced nutritional status rather than CFTR genotypes are the major determinants of aerobic exercise capacity in patients with CF