Middle-aged adults who have a sibling with cardiovascular disease (CVD) have a 45 percent increased risk for CVD, a risk that is greater than that conferred by having parents with CVD, according to a study in the December 28 issue of JAMA.

Cardiovascular disease in a first-degree relative confers increased risk for CVD, but whether familial CVD is truly an independent risk factor remains controversial, according to background information in the article. Risk associated with CVD in siblings is uncertain because published estimates are largely derived from case-control studies that generally lack sibling CVD event validation. Furthermore, estimates regarding magnitude of risk associated with a history of sibling CVD vary greatly. Accurate information about familial CVD will have increasing importance in prevention and treatment of CVD in the post-genome era.

Joanne M. Murabito, M.D., Sc.M., of the Framingham Heart Study, Framingham, Mass., and colleagues conducted a study to determine whether the occurrence of a validated sibling CVD event predicted CVD events in a cohort of middle-aged adults, and examined the impact of sibling CVD over and above that of parental CVD.

The researchers analyzed data from the Framingham Offspring Study, a part of the Framingham Heart Study, a population-based study initiated in 1948 with the offspring cohort initiated in 1971. Participants were members of the offspring cohort aged 30 years or older, free of CVD, and with at least 1 sibling in the study. All were followed up for eight years.

Among 973 person-examinations in those who had a sibling with CVD group (average age, 57 years) and 4,506 person-examinations in those with no sibling with CVD group (average age, 47 years), 329 CVD events occurred during follow-up. The researchers found that sibling CVD was associated with a 55 percent increased risk for incident CVD; this association persisted even after adjustment for risk factors (45 percent increased risk). The attributable risk percentage for sibling CVD was 27.4 percent; this represents the proportion of the 8-year CVD risk among those in the sibling CVD group that theoretically would not have occurred if members of the group had not had a sibling with CVD.

“Using validated events and a prospective design, our study substantially extends the knowledge base regarding the importance of sibling CVD. We observed that sibling CVD confers increased risks of CVD events above and beyond traditional risk factors and parental premature CVD. Thus, sibling CVD should be considered as important as parental premature CVD in the assessment of risk. Further investigation is needed to better understand why sibling history may be a stronger predictor for CVD than parental history, including exploration of the contribution of an early shared environment to increased sibling risk. Moreover, investigation of whether to incorporate sibling CVD as well as parental CVD into existing risk prediction and prevention algorithms is warranted,” the authors conclude.

(JAMA.2005; 294:3117-3123. Available pre-embargo to the media at http://www.jamamedia.org)