The odds of developing coronary heart disease or having a heart attack may partly lie in your genes.

Two new studies show that gene variants in a certain chromosome may make coronary heart disease — which is America's No. 1 cause of death — and heart attacks more likely.

The studies come from two separate research teams.

Together, the studies zero in on heart-related gene variants in chromosome 9p21. The scientists don’t know exactly what the gene variants do, but their findings suggest that the effects aren't good for the heart.

The studies appear in Science Express, which is the online early edition of Science.

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Coronary Heart Disease Study

The first study comes from researchers including Jonathan Cohen, PhD, of the University of Texas Southwestern Medical Center in Dallas.

They screened the DNA of more than 23,000 white people in Canada, the U.S., and Denmark.

A common variation in chromosome 9p21 was "consistently associated" with coronary heart disease, Cohen's team writes.

Half of the participants had one copy of the gene variant. An additional 20 percent to 25 percent had two copies of the gene variant.

People with two copies of the gene variant were 30 percent to 40 percent more likely to have coronary heart disease than people with no copies of the gene variant.

People with only one copy of the gene variant were about 15 percent to 20 percent more likely to have coronary heart disease than people with no copies of the gene variant, the study also shows.

The genetics of heart disease may differ among ethnic groups, note the researchers.

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Heart Attack Study

The second study comes from scientists including Augustine Kong, PhD, of Decode Genetics in Reykjavik, Iceland.

They studied more than 17,000 people of European descent in Iceland and the U.S., including nearly 4,600 heart attack patients.

In screening the participants' DNA, the researchers found a gene variant in chromosome 9p21 that was more common in heart attack patients.

About 21 percent of participants had two copies of the gene variant. They were 64 percent more likely to be heart attack patients, compared with people with no copies of the gene variant.

People with two copies of the gene variant were also twice as likely to have had a premature heart attack, defined as a heart attack before age 50 for men or age 60 for women.

The researchers aren't recommending gene tests, and they're not blaming the gene variants for all coronary heart disease or heart attacks.

The studies don’t include information on participants' diet, exercise, medical care, or other heart-related lifestyle habits.

Concerned about your heart risk? Your doctor can help you evaluate and upgrade your heart's health.

Click here to visit FOXNews.com's Heart Disease Center

This article was reviewed by Louise Chang, MD.

SOURCES: Helgadottir, A. Science, May 3, 2007; online "Science Express" edition. McPherson, R. Science, May 3, 2007; online "Science Express" edition. News release, Science.