The contribution of genes, environment and of body mass to blood pressure variance in young adult males

Objective: (1) To determine by means of multivariate genetic modelling whet her the covariation of blood pressure (BP) and body mass index (BMI) is com patible with a direct effect of BMI on BP, or rather with pleiotropy or env ironmental association, and (2) to quantify the contribution of such an eff ect and of heritability and environmental factors to BP variance. Design and methods: Fifty monozygous and 41 dizygous male twin pairs (ages: 17-38 years) were studied. BMI was calculated as weight/height(2). Blood p ressure was the mean of three conventional measurements in the supine posit ion. Estimates for the path coefficients of the three hypothesised models w ere obtained using Maximum Likelihood Estimation and were used to calculate the predicted covariance matrices for these models. A chi(2) goodness-of-f it index of P > 0.05 indicated an adequate fit. Likelihood ratio chi(2) sta tistics and the Akaike Information Criterion (AIC) were used to choose the best model among the fitting models. The path coefficients of the best mode l were used to estimate the variance decomposition of BP. Results: All hypothesised models fitted the data. The AIC was lowest for th e model representing an influence of BMl on BP, for both systolic (AIC = -2 2.3) and dia-stolic (AIC = -22.2) BP. The estimated percentages of the tota l phenotypic variance of BP, which could be explained by the influence of B MI on BP, were 11.4% and 12.9% for systolic and diastolic pressure respecti vely. The remaining variances were associated with Variation in genetic and environmental factors. Conclusions: A direct influence of BMI on BP consti tutes the most likely explanation of the BP-BMI-covariation and it accounts for about 12% of the BP-variance in young healthy men.