Genetic and environmental causes of variation in renal tubular handling of sodium and potassium: A twin study

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Abstract
We have conducted a study of renal sodium and potassium reabsorption in 205 pairs of twins on freely chosen diets; 89 of the subjects were studied on more than one occasion. Renal tubular sodium and potassium handling, as measured by the fractional excretions FENa and FEK, show repeatable differences between individuals.Siblings (in this case monozygotic and dizygotic pairs of twins) are more alike in this respect than unrelated individuals. Comparison of monozygotic and dizygotic twin pairs indicates that genetic, rather than shared environmental, factors are probably responsible for this similarity, with heritability estimates of 0.5 for sodium and 0.6 for potassium. There are indications of sex differences in the sizes of the genetic and environmental effects for both variables and indications that the genetic effects may be qualitatively different for FEK. Such findings need further investigation.