Scientists trying to understand why African-Americans are more likely than whites to die of heart disease may have hit upon a culprit -- a chemical that counteracts the body's clot-dissolving mechanism.
Dr. James Roberts, a cardiologist at the Johns Hopkins School of Medicine, said yesterday that blacks appear genetically predisposed to generate higher levels of a blood component called lipoprotein-a that keeps clots from breaking apart.
His remarks came yesterday during a conference on racial differences in heart disease sponsored by the Maryland chapter of the American Heart Association. The meeting was held at Harbor Court Hotel in Baltimore.
African Americans are more likely than whites to die of heart attacks, congestive heart failure and stroke -- and medical researchers aren't sure why. It's become a fertile area for research, with scientists exploring whether the differences are based in genetics or social factors such as poverty, diet and poor health care.
Several physicians speaking at the conference noted that heart disease and stroke are more prevalent among African-Americans than are cancer and AIDS -- both of which have drawn far more public attention.
Dr. Charles Francis, chief of medicine at Harlem Hospital in New York, said that a 1989 screening of Harlem residents found that 41 percent suffered from high blood pressure, a leading risk factor for heart attack, stroke and kidney disease.
Surprisingly, 80 percent of those with high blood pressure, also known as hypertension, were aware they had the condition -- but less than 1 percent had it under control.
Hypertension among African-Americans may be hard to treat for reasons of biology, he said, but the dismal state of health care in inner-city America is also to blame. There are few primary-care doctors in poor neighborhoods, and people who are placed on medication often stop taking the drugs because they do not appreciate the severity of their illness.
"Don't be lulled into a sense of complacency," Dr. Francis said. "Just because you are giving a particular medicine, it doesn't mean they are going to take it effectively or that the blood pressure is going to be controlled."
Dr. Roberts focused on a different problem -- the heightened tendency among African-Americans to form the blood clots that can interrupt circulation and trigger heart attacks.
His findings came from a continuing Hopkins study of people whose siblings have been diagnosed with heart disease. Because the condition tends to run in families, researchers are studying asymptomatic relatives to see what types of risk factors they carry. About 20 percent of the 137 research subjects are black.
When a clot starts to form, a natural chemical called plasminogen works to dissolve the clot and render it harmless. Blood tests of the black volunteers, however, showed that they generally had higher levels of harmful cholesterol called lipoprotein-a that prevents the natural clot-dissolver from acting.
"It keeps plasminogen from doing what it needs to do," Dr. Roberts said in an interview.
The role of lipoprotein-a must be studied further before it can be conclusively declared an enemy in the fight against heart disease. If it is, he said, there may be drugs or therapies that can lower a patient's risk.
He said one possibility for countering lipoprotein-a is niacin, a B vitamin, but more research is needed before anyone can make a recommendation.