Genetic regulation of plasma and red blood cell magnesium concentrations in man. I. Univariate and bivariate path analyses.

This paper concerns an analysis of family resemblance for magnesium concentrations, based on data from nuclear families and twins. Neither red blood cell magnesium nor plasma magnesium varies with age in children (under 20 years of age). Whereas adult plasma magnesium varies linearly with age, the red cell magnesium clearly showed a nonlinear trend: quadratic for males and a fifth-degree polynomial for females. Transformed magnesium concentrations generated six correlations in nuclear families and twins for each of the two traits. Separate univariate analyses, using a simple linear model with four parameters, strongly suggested that genetic factors are primarily responsible for the observed family resemblance. Both traits were then analyzed simultaneously using a simple bivariate model. We found that one common genetic factor alone could not explain all the 24 correlations generated for the bivariate analysis. The most parsimonious model involved only three parameters: genetic heritability for red blood cell magnesium (.922 +/- .014), genetic heritability for plasma magnesium (.721 +/- .040), and the genetic correlation between the two traits (.233 +/- .040).