AGE-SPECIFIC GENETIC-EFFECTS FOR BLOOD-PRESSURE

Correlations between relatives were determined for systolic and diasto lic blood pressure. The correlations decrease as age differences betwe en relatives increase in a Norwegian sample with 43 751 parent-offspri ng pairs, 19 140 pairs of siblings, and 169 pairs of twins. A simple b iometric model specifying only age-specific genetic additive effects a nd environmental effects fitted well to correlations between cotwins, pairs of siblings, and parent-offspring dyads in subsets of relatives grouped by age differences. None of the environmental effects appeared to be due to environmental factors that are shared by family members. Models that excluded a parameter for the age-specific genetic influen ce did not fit the data. The results may partly explain what seems to be a discrepancy between relatively low parent-offspring correlations from previous nuclear family studies and high correlations from twin s tudies, especially in identical twins.