Genetic analysis of systolic blood pressure in Melbourne families.

1. Circumstantial evidence suggests that immunological mechanisms might contribute to hypertension in man. If so, it would be expected that those genetic loci which influence the human immune response would also influence the risk of hypertension. 2. To test this hypothesis, the distribution of systolic blood pressure (SBP) was studied in seventy-eight families comprising 437 adults ascertained through fifty-eight probands with hypertension and twenty probands with low to normal levels of blood pressure. After allowing for the method of ascertainment of the families, and adjusting for the effects of age and sex, about 55% of the phenotypic variance of SBP could be attributed to genetic factors including 23% (42% of the additive genetic variance) attributable to the effects of immunogenetic loci (HLA and Gm). 3. This suggests that relatives with a greater number of HLA and Gm haplotypes in common had more similar SBP levels than similar relatives with fewer HLA and Gm haplotypes in common. This finding supports the hypothesis that immunological mechanisms contribute to hypertension in man.