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Genetics and heart disease
For the first time in history, the human genome—all 22 chromosomes—has been mapped. In 2003, the U.S. Human Genome Project was completed, a 13-year effort coordinated by the U.S. Department of Energy and the National Institutes of Health. A full genome map can provide physicians, who have known for many years that the strongest predictor of heart disease is a positive family history, with critical information for treating patients.

“Almost 80 percent of heart disease has a genetic basis. But you can’t choose your parents!” says Palmetto Health Heart Hospital cardiologist Dr. Joe Hollins. “There also is a strong gene-environment interaction in most causes of heart disease. So, many people can use diet, exercise, and weight control to modifiy their genetic predisposition to developing atherosclerosis, or the build-up of fatty plaques in the arteries.”

An example of how a person can work against a predisposition is a gene located on chromosome #19, a gene commonly referred to as the “thrifty gene” which predisposes people to store fat. “Ten thousand years ago, when it was highly likely that a person would go two days without food, such a gene helped people store fat for survival,” says Dr. Hollins.

Today, if a person never misses a meal and does not exercise, the “thrifty gene” can be a deadly disadvantage, putting a person at risk of weight gain and lipid abnormalities. This gene also is dominant, which means that 50 percent of the person’s siblings and children will have it. Diet, exercise, and controlling weight gain can at least control the environmental factors that “turn on” these genes.

Another dominant gene is Lipoprotein(a), Lp(a), present in about one-third of patients with atherosclerotic cardiovascular disease. A strongly positive family history of atherosclerosis is one of the most common causes of premature coronary artery disease (CAD). Presence of the gene for Lp(a) is a common cause of early coronary bypass surgery failure and a carotid atherosclerosis, or premature strokes.

“Unlike the thrifty gene, Lp(a) is not influenced by environmental factors like diet or exercise,” says Dr. Hollins. “A simple blood test detects the level of Lp(a). High Lp(a) levels are best treated with drug therapy.”

There are genotype tests available that can help determine your response to diet and exercise. For example, a person with ApoE4 genotype who is trying to lower his or her cholesterol will achieve better results with a diet very low in saturated fat. A person with ApoE2 genotype is most responsive to exercise and less responsive to a low fat diet.

“Some patients are very responsive to a low-fat diet and not responsive to exercise, which can explain why a marathon runner can develop premature atherosclerosis. Others greatly benefit from exercise and need a diet higher in monounsaturated fat,” says Dr. Hollins. “This is a perfect example of how different we are genetically, and demonstrates how differently we respond to our environment.”

This type of genotype testing currently is available from a single blood test, and is a result of genetic studies yielding critical information on how to reduce the rise of heart disease.

Information from human genome studies likely will serve as a foundation for further detailed patient characterization. This will allow individualized care plans and treatment beyond the traditional risk-factor modification approach.