Researchers say the study, which appeared last month in the journal Circulation, points to the need for further research to determine whether African-Americans have a genetic mechanism that protects them from the risks of lipoprotein(a), also known as Lp(a). If such a mechanism is found, doctors might be able to use the information to develop therapies and drugs that reduce heart-attack risks for everyone.
In the study, statisticians from Rice University in Houston and medical researchers from The University of Texas Southwestern Medical Center at Dallas conducted a statistical analysis that looked for a relationship between increased levels of Lp(a) and increases in coronary calcium, a leading indicator of coronary atherosclerosis.
"We know from prior research that elevated plasma levels of Lp(a) are an independent risk factor for cardiovascular disease among whites, and we also know that African-Americans have twofold to threefold higher plasma levels of Lp(a) than whites, but they do not have a correspondingly higher rate of heart attacks," said Rudy Guerra, professor of statistics at Rice and the lead author of the paper. "Our study found no independent relationship between plasma levels of Lp(a) and coronary calcium in either whites or African-Americans, which indicates that some other mechanism is at work."
The Dallas Heart Study is a groundbreaking multiethnic investigation of cardiovascular disease involving thousands of Dallas County residents, and it contains the most representative sample of African-American subjects of any other statistical dataset ever used to study Lp(a) and coronary artery calcium levels. In the latest study, scientists looked at the records of 1,288 subjects over the age of 40 -- 380 black women and 241 white women over 45; and 381 black men and 286 white men over 40 -- whose coronary calcium levels had been determined via electron beam computer tomography and whose Lp(a) levels were determined via blood tests.
The study was designed to test one of the leading theories that aim to explain why increased levels of Lp(a) in the bloodstream lead to different risk factors for whites and African-Americans.
That theory is based on earlier lab studies that showed Lp(a) had a tendency to stick to some of the tissues that line blood-vessel walls. Some researchers believe the adhesive property causes a chain reaction in which first LDL cholesterol and then calcium builds up on the inner walls of blood vessels. Although African-Americans typically have two to four times the amount of Lp(a) in their blood as whites, the Lp(a) proteins in whites tend to be shorter and stickier than the Lp(a) in African-Americans.
"We found no evidence to support a relationship between the protein's size and related levels of atherosclerosis in any of the groups we studied," said Guerra.
The research was supported by the Donald W. Reynolds Foundation and the National Institutes of Health.