The determination of carotid intima medial thickness in adults--a population-based twin study.

Introduction: Although cardiovascular events are known to cluster in families it is unclear the extent to which atherosclerosis per se is genetically determined. The aim of this study was to assess the heritability of carotid intima media thickness (IMT) measurements, a surrogate marker of early atherosclerosis, using a population-based twin study methodology.
Methods: B-mode carotid artery ultrasound images were acquired on 264 twin subjects (142 monozygotic (MZ); mean age 54.3 years and 122 dizygotic (DZ); mean age 51.7 years). An estimate of genetic determination, heritability, was calculated for the IMT parameters before and after correction for confounding variables.
Results: An increased carotid IMT was associated with known cardiovascular risk factors (total cholesterol r=0.24, P<0.001 and systolic blood pressure r=0.42, P<0.001) and with a history of coronary events (0.79+/-0.12 vs. 0.72+/-0.14, P=0.01). Carotid IMT measurements demonstrated a familial influence (intra-class correlation of 0.54 for MZ vs. 0.39 for DZ) but no specific genetic determination (heritability estimate 0.31, P=0.15).
Conclusion: Within a normal population carotid IMT is under a familial, but not genetic influence. The mechanism of genetic control over cardiovascular events may not be mediated through atherosclerotic load as measured by IMT.