Genetic and environmental contributions to atherosclerosis phenotypes in men and women: Heritability of carotid intima-media thickness in the Framingham Heart Study

Carotid intima-media thickness (IMT) is a quantitative measure of subclinical atherosclerosis that is predictive of subsequent myocardial infarction and stroke. There is controversy regarding the proportion of variability in IMT explained by genetic factors. Thus, it is uncertain whether carotid IMT is a heritable trait that can be used in genetic studies. From 1996 to 1998, we measured carotid IMT in 906 men (mean age, 56.7 years) and 980 women (mean age, 57.4 years) from 586 extended families (1630 sib pairs) in the Framingham Offspring cohort. B-mode carotid ultrasonography was used to define mean and maximum IMT of the common carotid artery (CCA) and internal carotid artery (ICA). Correlation coefficients were calculated in pairs of siblings. Variance component methods were used to estimate heritability with crude, age- and sex-adjusted, and multivariable-adjusted normalized deviates. Multivariable-adjusted correlation coefficients for mean CCA and ICA IMT were 0.16 and 0.16, respectively. Crude, age- and sex-adjusted, and multivariable-adjusted heritabilities were 0.67, 0.44, and 0.38 for the mean CCA IMT (all P