Genetic Link Seen in Early Heart Disease

Study finds insulin resistance in families with a history of the disease

FRIDAY, Aug. 10, 2001 (HealthDayNews) -- Half of all early heart disease cases can be blamed on genes rather than lifestyle, a Finnish study suggests.

Researchers are trying to determine whether lifestyle -- fatty foods, smoking, lack of exercise -- or a "bad heart gene" are at the root of a history of heart disease in families. Now a closer look at those with early coronary heart disease shows that insulin resistance runs in families, providing even more evidence that genes are the culprit.

"It was previously thought that the classic risk factors -- high total and LDL [good] cholesterol, elevated blood pressure, and smoking -- determined the risk of early-onset cardiovascular disease," study author Dr. Markku Laakso, chairman of the department of medicine at the University of Kuopio, says in an e-mail interview. "Because insulin resistance is so prevalent . . . and is an increasing problem in Western societies, we wanted to investigate its role in increasing the risk of cardiovascular disease early in life."

Laakso and his colleagues studied 101 families in which at least two siblings had experienced early heart disease and compared those siblings to a third unaffected by heart disease.

The researchers looked for a combination of known risk factors for heart disease -- central obesity (excessive fat tissue in the abdominal region), insulin resistance, high levels of fat in the blood, and low HDL ("good") cholesterol as well as high blood pressure.

Laasko then tested all those who had no previous diagnosis of diabetes by feeding them sugar. After one hour and two hours, he measured their blood sugar, insulin and cholesterol levels.

Those with early heart disease had higher insulin levels than the siblings who didn't, even if they didn't have diabetes. They also had higher levels of blood fat (triglycerides) and lower levels of "good" cholesterol, the researchers found. This occurred although the lifestyle factors such as smoking were the same between both groups.

The study indicates that traditional risk factors for cardiovascular heart disease -- high cholesterol, high blood pressure, smoking, and obesity -- account for only half of the risk for early onset of the disease, Laakso says. Early heart disease was defined as narrowing of two arteries in men under the age of 55 and in women under the age of 65.

"We know that insulin resistance is an inherited trait and is related to several cardiovascular risks," Laakso explains. "And what we found was that insulin resistance syndrome clustered in families with early-onset cardiovascular disease."

"The finding means that in prevention of cardiovascular disease, the treatment of the classic risk factors -- obesity, high triglycerides, low HDL cholesterol, risk for thrombosis -- is not enough. Risk factors related to the insulin resistance should be equally treated," he says.

The findings were published in the August issue of Arteriosclerosis, Thrombosis and Vascular Biology.

According to the American Diabetes Association, as many as 10 to 20 percent of Americans may suffer from insulin resistance syndrome -- also known as Syndrome X -- though there are no statistics on exactly how many people have the condition. The American Heart Association has called for further study of the cluster of conditions to understand how they interact to cause heart disease.

The findings are a confirmation and a message to health-care professionals, says Barbara Howard, president of the MedStar Research Institute, the research arm of the largest nonprofit healthcare group in the Washington D.C./Baltimore area.

If they have insulin resistance, Howard says, "younger patients -- even if they don't smoke, even if their LDL cholesterol is normal, even if their blood pressure is not elevated -- are still at risk for cardiovascular heart disease."

"A lot of doctors look at a patient and say: 'They don't smoke, they don't have high blood pressure -- I don't have to worry about heart disease,'" Howard continues. "But if those patients have an apple-shaped body versus a pear-shaped body, what we call central obesity, and their blood fats are out of whack, these people need to be monitored and viewed at risk, even if they are young."

What To Do

For more on insulin resistance and heart disease, see the American Academy of Family Physicians or the San Francisco Medical Society.

SOURCES: Interviews with Markku Laakso, M.D., chairman, department of medicine, University of Kuopio, Finland (via e-mail); Barbara Howard, Ph.D., president, MedStar Research Institute, Washington, D.C.; August 2001 Arteriosclerosis, Thrombosis and Vascular Biology
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