Are some people genetically predisposed to hyponatremia due to high sweat sodium losses?
A distinguishing characteristic of cystic fibrosis (CF) is salty sweat. CF is caused by a defect in a gene that encodes for a protein involved in the transport of chloride—and indirectly sodium—out of the sweat duct. (Davis, 2001; Quinton, 1999). This would explain the predominant characteristic of CF—high levels of sodium and chloride in sweat. CF is most prevalent in those of Northern and Central European heritage, where up to 1 in 20 carries a recessive gene for CF. Less than 1% of CF patients have sweat sodium or chloride levels less than 60 mmol/liter (Davis, 2001); for that reason, high sweat electrolyte concentrations are used as diagnostic criteria. Although there is some evidence that individuals with CF are susceptible to hyponatremia (Montain et al., 2001; Smith et al., 1995), additional research is needed to determine just how prevalent the CF gene is among those who develop hyponatremia. What fluid-replacement guidelines should athletes follow? It is well established that
