AAN: Relative Risk: Ischemic Stroke is a Family Affair

BOSTON -- Siblings of middle-age stroke patients have nearly twice the risk of strokes themselves compared with the average American.

BOSTON, May 4 -- Siblings of middle-age stroke patients have nearly twice the risk of strokes themselves compared with the average American.

Among 807 brothers and sisters of 181 men and women who had strokes or TIAs before the age of 65, the relative risk for stroke was 1.92, compared with national stroke prevalence estimates, said Lynda D. Lisabeth, Ph.D., of the University of Michigan, and colleagues, at the American Academy of Neurology meeting here.

The risk for stroke among the siblings of stroke victims was particularly high among Mexican Americans in general, and Mexican-American men in particular in a community-based study, reported co-author Lewis B. Morgenstern, M.D., also of the University of Michigan in Ann Arbor.

"If we compare Mexican Americans to non-Hispanic whites, we find that the risk to the sibling is especially prominent in Mexican Americans, with over a doubling of the risk compared to the general population," said Dr. Morgenstern. "The risk is not as substantial in non-Hispanic whites as it is Mexican Americans."

Among non-Hispanic whites, only the siblings of women who had strokes were at increased risk for a stroke.

The data came from the BASIC (Brain Attack Surveillance in Corpus Christi) study, a population-based stroke study comparing stroke Mexican Americans and non-Hispanic whites in Corpus Christi, Tex.

The authors looked at family groupings of patients who had ischemic strokes or TIA from the ages of 45 to 64. A random subset of patients were interviewed to determine the number of biologic siblings and the history of stroke among them.

The investigators calculated relative risk ratios for the overall population and by ethnic background, using national prevalence estimates for the general population.

They found that overall, siblings of stroke victims had a relative risk for stroke of 1.92 (95% confidence interval, 1.39-2.61) Among Mexican Americans as a whole, the risk was exactly double (relative risk 2.00, 95% CI, 1.39-2.81).

This result was because of a significantly higher risk among siblings of Mexican-American men who had stroke (relative risk 2.61; 95% CI, 1.64-3.99); the relative risk for siblings of Mexican Women was not significant (1.47, 5% CI: 0.83-2.46).

Among non-Hispanic whites, only the brothers and sisters of women who had stroke were themselves at increased risk for stroke (relative risk 2.76, 95% CI, 1.22-5.66).

Because this was a population-based study, the authors were not able to control for potential confounders such as genetics, environment, cultural differences, or familial factors, Dr. Morgenstern said.

"We've already shown in other research that Mexican Americans have a higher risk of stroke compared to non-Hispanic whites, and on top of that we're now able to show that their siblings have more risk of stroke, they have more siblings [than whites], and are more likely to be in the same geographic area [as siblings], which makes them a great population to study as we further genetics research," he concluded.