The importance of genetic and environmental effects for pre-eclampsia and gestational hypertension: a family study

Objectives To determine the importance of genetic effects in the aetiology of pre-eclampsia and gestational hypertension and to investigate whether pre-eclampsia and gestational hypertension share genetic aetiology. Design Individual record linkage between the population-based Swedish Multi-Generation and the Medical Birth Registers. Setting Sweden. Population 1,188,207 births between 1987 and 1997 and their parents. Methods Similarities in relatives were measured by the number of pairs concordant and discordant for disease, the odds ratio (OR) and tetrachoric correlations. Estimates of genetic and environmental effect for gestational hypertension, pre-eclampsia and pregnancy-induced hypertension were calculated from structural equation model fitting. Main outcome measures Pre-eclampsia and gestational hypertension. Results Full sisters and mother-daughters were more similar for pre-eclampsia (OR 3.3, 95% confidence interval [CI] 3.0-3.6 and OR 2.6, 95% CI 1.6-4.3, respectively) than half-sisters (maternal half-sisters OR 1.4, 95% CI 0.9-2.2 and paternal half-sisters OR 1.0, 95% CI 0.6-1.6). Full sisters and mother-daughters were also more similar for gestational hypertension than half-sisters. A full sister to a woman with pre-eclampsia also had a significantly increased risk of gestational hypertension (OR 2.5, 95% CI 2.2-2.8). In contrast, the risk for half-sisters was not increased. Model fitting suggested heritability estimates for pre-eclampsia of 31%, for gestational hypertension 20% and for pregnancy-induced hypertension 28%. Conclusions There is a genetic component in the development of pre-eclampsia and gestational hypertension and the pattern of co-morbidity suggests that they may share part of their genetic aetiology. This could be important for studies of potential susceptibility genes for these diseases.