Genes linked to cardiovascular disease more common among African Americans than those of European descent

Three gene variants that have been associated with heart attack risk in Japanese studies occur more frequently among African Americans than those of European descent, but it is not clear whether these genes play a role in racial disparities in cardiovascular disease in the United States, according to a new study in the July 7, 2004 issue of the Journal of the American College of Cardiology.

“This is simply a look at the topography of these genetic polymorphisms (variations) in African Americans and European Americans. The polymorphisms have not been proven to be associated with heart attacks in African Americans or European Americans; however, they have been convincingly associated among Japanese. Larger association studies comparing subjects with and without disease, in both African Americans and European Americans will be needed to draw more definitive conclusions. But our data is provocative in that it strongly suggests this hypothesis needs to be further tested,” said Howard L. McLeod, PharmD, at the Washington University School of Medicine in St. Louis.

For this study, the researchers collected blood samples from 95 African American and 95 European American healthy volunteers. Complete genotype information was obtained for 88 of the African Americans and 91 of the European Americans.

All three genotypes that have been associated with heart attack risk in Japanese studies were found in both groups in this study. Two of the gene variants were significantly more common among the African American volunteers than among the European American volunteers. About 9 percent of those in the African American group had all three “risk-associated” gene variants, while none of the European Americans did. The likelihood of observing two or more of the “risk” variants was 51 percent among the African American volunteers, but only a little more than 3 percent among the European Americans.

The study’s lead author, David E. Lanfear, MD, said this research takes a genetic approach to questions that have usually been approached from a sociological angle.

“Most previous studies have looked at socioeconomic factors, factors related to the access to medical care, differences in the treatments that patients receive, while the possible role of genetics has been less explored. We looked to see if polymorphisms associated with heart attack risk among Japanese have differing frequencies in other racial groups,” Dr. Lanfear said.

While intriguing, the researchers noted that these results do more to raise questions than to provide answers.

“Our results, showing markedly higher frequencies of both single and compound risk-associated genotypes in African Americans than in European American subjects, suggest a potential genetic contribution to the observed racial differences in coronary heart disease risk. However, this should be interpreted with caution because the frequency of these genotypes in African Americans is greater than the observed incidence of coronary heart disease and heart attack in this population. This raises the question of whether these risk-associated genotypes carry the same significance in African Americans as has been shown in Japanese subjects,” the researchers wrote in their article.

Nanette H. Bishopric, MD, FACC at the University of Miami in Florida, who was not connected with this study, said the main value of these results is to provide clues for further study, and she warned against over-interpreting these results.

“All they’ve done is they’ve shown the incidence of these SNPs (Single Nucleotide Polymorphisms) is high, they have not shown a statistical correlation between heart attacks in blacks and the presence of those SNPs,” Dr. Bishopric said.

Dr. Bishopric also pointed out that even with further research, these genes may not ever become useful in predicting heart attack risk in African Americans. Because these particular gene variations appear to be so common among African Americans, genetic tests probably would not be able to help doctors differentiate between people who may be more likely or less likely to develop heart disease.

The American College of Cardiology, a 29,000-member nonprofit professional medical society and teaching institution, is dedicated to fostering optimal cardiovascular care and disease prevention through professional education, promotion of research, leadership in the development of standards and guidelines, and the formulation of health care policy.