For a study, it was determined that human skeletal muscle cells carry the cystic fibrosis transmembrane conductance regulator (CFTR). Variations in CFTR functioning among cystic fibrosis patients may be a key factor of cystic fibrosis patients’ maximal exercise capacity. There have been few conflicting investigations on the association between CFTR genotype and maximal exercise capacity. The study looked at the factors influencing maximal exercise capacity, as measured by peak oxygen uptake (V.o2peak), in children and adults with cystic fibrosis. In an international, multicenter, cross-sectional study, researchers collected data on CFTR genotype and cardiopulmonary exercise tests in cystic fibrosis patients aged 8 and up. Functional classifications I–V were assigned to CFTR mutations.

The final analysis included 726 patients (45% females; ages 8–61 years; predicted forced expiratory volume in 1s, 16 to 123%) from 17 cystic fibrosis centers across North America, Europe, Australia, and Asia. They all had valid maximal cardiopulmonary exercise tests and complete CFTR genotype data. In general, patients had exercise intolerance (V.o2peak, 77.3±19.1% predicted), although the findings were consistent among CFTR classes. In comparison to classes IV–V, they found no connection between CFTR genotype functional classes I–III and either V.o2peak (percent predicted) (adjusted =0.95; 95% CI, -4.18 to 2.29; P=0.57) or maximal work rate (Wattmax) (adjusted =-1.38; 95% CI, -5.04 to 2.27; P=0.46). V.o2peak (= -8.24%; 95% CI, -14.53 to -2.99; P=0.003) and Wattmax (adjusted =-7.59%; 95% CI, -14.21 to -0.95; P=0.025) were significantly lower in those with at least one copy of an F508del-CFTR mutation and one copy of a class V mutation than those with two copies of a class II mutation. In a linear regression analysis adjusted for pertinent variables, lung function and body mass index link to V.o2peak.

In patients with cystic fibrosis, the functional genotype class of the CFTR gene was not linked to maximum exercise capacity; however, for those with at least one copy of an F508del-CFTR mutation and a single class V mutation had a reduced maximal exercise capacity.