According to a study as many as half of the children and siblings of individuals with diseased coronary arteries may have signs of atherosclerosis, even though they have no symptoms of heart or vessel disease.

"We've known that family history is a risk factor for heart disease, however that relationship has been associated with secondary risk factors such as high cholesterol, hypertension and diabetes," says K. Lance Gould, professor of medicine at the University of Texas Medical School at Houston.

Gould says doctors can find heart and blood vessel disease early in these high-risk individuals - before it has caused any clinical signs such as a heart attack, stroke or chest pain - using positron emission tomography (PET) imaging.

Positron emission tomography is a highly accurate, non-invasive test that can make images of the blood flow inside the heart muscle, an indication of how well the coronary arteries are working. PET imaging is available at about 40 U.S. medical centers.

The researchers studied 90 subjects, including 18 people with coronary artery disease and 32 of their immediate family members (i.e. parents or siblings) who had no symptoms of heart disease. In addition, they had two control groups: one made up of 30 individuals who had heart disease risk factors but no family history of the disease, and a second made up of 10 people with no risk factors and no close relatives with heart or vessel disease.

Study participants underwent PET imaging after they were given the drug dipyridamole, which mimics the way exercise, increases blood flow in the heart muscle. The reason for administering dipyridamole is to see how the heart responds to physical stress. Someone without symptoms of heart disease may have normal blood flow in their heart under resting conditions. However, abnormal blood flow when the heart is stressed may indicate the very early stages of coronary artery disease.

In response to the drug, 50 percent of the people who had no symptoms but had a family history of heart disease had abnormal blood flow in their hearts, indicating very early atherosclerosis.

Gould offers the example of one participant, a 73-year-old woman, who had been diagnosed with coronary artery disease. Researchers confirmed her diagnosis by arteriography, or ultrasound of her arteries, that showed mild disease in three arteries. Her three sons - ages 43 to 55 years and with no symptoms of vessel disease - underwent PET imaging, and all three of them showed mild-to-moderate 3-vessel coronary artery disease.

Also, defects shown on PET images were similar between individuals who had high or normal levels of low-density lipoprotein (LDL) cholesterol (the "bad" cholesterol).

"Therefore," Gould says, "the influence of family history on the size and severity of defects shown by PET imaging is independent of cholesterol levels." In fact, researchers showed abnormal PET results in five of 10 people with no other risk factor except family history.

In addition, the researchers note that family history was associated with more extensive disease (larger defects), but not more severe disease (intensity of defects as shown on PET image) compared with subjects who had other risk factors for heart disease, but no family history of it. Gould says this could be due to more diffuse disease in immediate family members compared to controls.

"It is important that we can identify atherosclerosis at such an early stage in this particular high-risk group," he says. "These individuals are easy to identify because of the family history, and we can step-up treatment and prevention efforts long before they experience a coronary event."

Treatment or prevention may include dietary measures to keep body weight under control and increasing exercise, in addition to prescribing cholesterol-lowering drugs even for people with normal cholesterol levels, Gould says.

Studies have shown that if you reduce cholesterol to lower-than-normal levels, it may prevent the development of coronary artery disease and coronary events in these individuals, he adds.