ith completion of the human genome sequence, expectations are rising that a detailed catalogue will soon be available of all important common genetic susceptibility variants for human diseases, including coronary heart disease (CHD) and related atherosclerotic cardiovascular disease (CVD). 1 In light of this seminal event in medical research, it is curious that the family history of CHD has not been accorded a more central role in risk prediction and disease prevention by clinicians and public health professionals. A positive family history of CHD is present in the majority of cases of premature-onset CHD. 2 In cases of familial hypercholesterolemia and other rare forms of premature-onset CVD, CHD clearly segregates in a mendelian fashion. For most cases of premature-onset CHD, the mode of genetic transmission in families is less clear. Although the family history of CHD has been considered a putative risk factor for decades, it has not been incorporated along with other established risk factors such as hyperlipidemia, hypertension, and cigarette smoking in some widely applied multivariable risk algorithms, 3 though other risk algorithms do incorporate family history information. 4
See p 2150This cautious approach to widespread application of family history information is not due to insufficient evidence. Risks for CHD death are greatest in monozygotic (identical) compared with dizygotic (nonidentical) twins, particularly when there is a premature (eg, Ͻ65 years) age of onset in the initially affected twin. 5 In multiple prospective studies involving hundreds of thousands of men and women, a parental history of premature CHD is a significant risk factor for CVD even after multivariable adjustment. Relative risk estimates generally range from 1.2 to 2.0, as noted in the Physician's Health Study and Women's Health Study, 6 although the estimated magnitude of risk associated with early-onset parental disease is substantially higher in some studies. 7 However, what has remained unclear are the pathophysiological/genetic mechanisms of the familial risk, the extent to which familial risk is independent of other established risk factors (including hyperlipidemia, hypertension, and tobacco use, which have a familial component), the magnitude of excess risk after adjustment for other risk factors, and the extent to which risk conferred by a positive family history of CHD is modifiable.In this context, Nasir et al 8 in this issue of Circulation provide a fascinating and timely contribution to the family history literature. The authors examined the association of a reported family history of early-onset (before age 55 years) CHD with the presence and burden of coronary artery calcium (CAC) in electron beam computed tomography in 8549 asymptomatic men and women referred for testing. 8 CAC is a surrogate measure of the presence and burden of coronary atherosclerosis that has consistently been associated with increased risks for CHD in selected cohorts. 9 CAC was significantly more common in subjects with a sibling or parenta...