Cardiovascular risk factors in a French Canadian population: resolution of genetic and familial environmental effects on blood pressure using twins, adoptees, and extensive information on environmental correlates.
Genetic and environmental influences on systolic (SBP), diastolic (DBP), and mean arterial (MBP) blood pressure were examined using an expanded version of a path model in which parents and their singleton, twin, and adopted offspring were incorporated, and which also included an environmental index as an estimate of the underlying familial environmental component. Estimates of genetic heritability are lower in parents (10-15%) than in offspring (40-50%). Cultural heritability was significant for SBP (0.31) and MBP (0.40), and an intergenerational effect was found for DBP, with higher estimates in parents (0.42) than in offspring (0.21). Marital resemblance was significant, and no support was found for differential maternal and paternal cultural transmission. Two novel results arising from this study are 1) gender-specific sibling effects, with greater female than male resemblance for SBP and MBP and the opposite pattern for DBP, and 2) the suggestion of extra twin resemblance arising on account of additional shared environments and resulting in greater like-sex than opposite-sex twin resemblance. The major conclusions drawn from this study are that 1) parameter estimates are stable with or without the use of extensive environmental indices, and 2) the addition of twins and adoptees did not significantly impact the results, with the exception of a possible influence of the adoptees in estimates of cultural heritability for DBP. Combining both these features (i.e., extended relatives and environmental indices) enables testing for additional sources of familial aggregation, which is not possible using the traditional nuclear family approach and results in a more accurate assessment of the relative roles of heredity and environment on blood pressure than has been previously possible.