CFTR genotype-related body water and electrolyte balance during a marathon

The aim of this investigation was to determine the influence of CFTR genotype on body water and electrolyte balance during a marathon. Fifty-one experienced runners completed a marathon race. Before and after the race, body mass and a sample of venous blood were obtained. During the race, sweat samples were collected using sweat patches, and fluid and electrolyte intake were obtained using self-reported questionnaires. Thirty-eight participants (74.5% of the total) were 7T/7T homozygotes, 11 (21.6%) were 7T/9T heterozygotes, and one participant presented the rare genotype 5T/7T. Another participant with 9T/9T presented the mutation p.L206W. Participants with 7T/7T showed higher sweat sodium concentrations (42.2 +/- 21.6mmol/L) than 7T/9T (29.0 +/- 24.7mmol/L; P=0.04). The runner with the 5T/7T genotype (10.2mmol/L) and the participant with the p.L206W mutation (20.5mmol/L) exhibited low-range sweat sodium concentrations. However, post-race serum sodium concentration was similar in 7T/7T and 7T/9T (142.1 +/- 1.3 and 142.4 +/- 1.6mmol/L, respectively; P=0.27) and did not show abnormalities in participants with the 5T/7T genotype (140.0mmol/L) and the p.L206W mutation (143.0mmol/L). Runners with the CFTR-7T/7T genotype exhibited increased sweat sodium concentrations during a marathon. However, this phenotype was not related with increased likelihood of suffering body water and electrolyte imbalances during real competitions.