Longitudinal Twin Study - Cohort Study of Blood Pressure

BACKGROUND: Identifying individuals at a young age who are at risk for future development of hypertension in adult life is a public health issue of great importance. The imperfect nature of blood pressure tracking throughout childhood and adolescence, and the fact that the genes which determine blood pressure in childhood may not be the same ones which operate in adulthood make it clear that improved predicting models are needed. The twin-parent study design allowed testing more subtle genetic and environmental hypotheses than was possible with nuclear families or twins alone. The longitudinal component permitted an analysis of developmental changes in the genetic expression of the hemodynamic determinants of blood pressure. The inclusion of unlike sex twins permitted an analysis of the consistency of genetic and environmental effects across the sexes. DESIGN NARRATIVE: The longitudinal comparison of the cardiovascular responses of adolescent twins and their parents was initialed in 1983. Three cohorts of twin families were enrolled, each cohort beginning 18 months apart. Both monozygotic and dizygotic twins were included. Variables measured included demographics, family history, personality, blood pressure, anthropometry, stage of puberty, dynamic exercise, isometric exercise, psychological stress, echocardiography, genotyping, and lipid profiles. Each cohort revisited every 18 months. A fourth cohort of 330 preadolescent twin pairs stratified by sex and zygosity was recruited from an established population-based twin registry. The hemodynamic determinants of blood pressure were assessed by non-invasive measurements of cardiac function including echocardiography and response to isometric and dynamic exercise. Zygosity was determined by questionnaire and confirmed by dermatoglyphic analysis and blood group tests. Anthropometric and hemodynamic measurements in the parents were compared to those in the children. The study included up to five sets of longitudinal measurements, thereby permitting an evaluation of whether the same or different genes operated at different ages encompassing pre-puberty, puberty, and post-puberty.