In a study of families with early heart disease, researchers have found that genes play a large role in early-onset coronary heart disease (CHD), which clusters in families regardless of environmental factors.

Researchers concluded that the traditional risk factors for CHD - such as high cholesterol, high blood pressure, smoking, and obesity - account for only half of the risk for CHD. Genetic factors may explain the other 50% of the risk for CHD in men younger than 55 and women younger than 65.

One of the most common disorders than runs in families is "syndrome X," or insulin resistance syndrome, which causes high levels of total cholesterol, high levels of LDL, the "bad" cholesterol, and low levels of HDL, the "good" cholesterol. In this study, those with CHD exhibited those characteristics; they also had higher insulin levels than their siblings without heart disease.

Lifestyle factors such as obesity, alcohol use, smoking, and physical activity were not different between those who had CHD and their siblings who did not. Therefore, the difference in risk is more likely due to genetic factors.

The study, which was published in the August issue of the AHA journal Arteriosclerosis, Thrombosis and Vascular Biology, concluded that more research is needed to identify a gene that predisposes individuals to early CHD.

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