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Irregular Heartbeat Gene Found

Millions of Africans and African-Americans carry a version of a gene that raises their risk of abnormal heart rhythms, which can be deadly, researchers reported Thursday.

The gene variant, which seems to be exclusive to people of African descent, might be used in the future to screen people most at risk -- who could then avoid certain drugs that can activate the arrhythmia, the researchers said.

People with structural heart disease known as cardiomyopathy, or with low blood potassium, also can develop arrhythmias if they have the variant, according to Dr. Mark Keating of Children's Hospital and Harvard Medical School in Boston and colleagues.

"This variant by itself doesn't cause disease," Keating said in a telephone interview, referring to the gene.

"You need a cardiomyopathy or there are hundreds of medications that can affect it," he added, naming certain antibiotics, antihistamines, especially seldane, and tricyclic antidepressants.

The National Heart, Lung and Blood Institute, which helped pay for the study, estimates that 4.6 million U.S. blacks carry the gene variant.

"This is good news for the individual and good news for the physician," Keating said. People can predict their risk of developing such an arrhythmia.

"You can actually die of your first arrhythmia and not have a second shot at it."

The gene, called SCN5A, affects a molecular structure called a cardiac sodium channel, Keating and colleagues report in Friday's issue of the journal Science.

It helps start a heartbeat by allowing sodium to flow across the membrane of the cardiac muscle cell.

The variant form of the gene, called Y1102, creates sodium channels that stick open a bit longer than normal. This can lead to an abnormal heart rhythm.

The gene variation could become a concern only if a patient's heartbeat is already affected by other factors. The most common is a severely reduced level in the blood serum of electrolytes — potassium, calcium, sodium and magnesium — which are chemicals affecting cardiac rhythm. Electrolyte levels can be decreased by extreme exercise or by many of the common medications used to control blood pressure or eliminate excess fluids.

Such arrhythmias kill 450,000 Americans a year. Heart attacks are a leading cause of arrhythmia, as is heart disease.

Keating, working with colleagues at the University of Utah, Columbia University and St. George's Hospital Medical School in London, said 13.2 percent of 205 African-Americans they studied had at least one copy of the variant gene.

It turned up in 19.2 percent of the 468 West Africans and Caribbeans the researchers looked at. "It is more common in Africans than in African-Americans," Keating said.

The gene variant was not found in screenings of white and Asian patients and in only one of 123 Hispanic patients tested.

Dr. Peter Spooner of the National Heart, Lung and Blood Institute, one of the National Institutes of Health, said the Keating study "is the start of the payoff from work on the human genome. Scientifically, this is pretty significant."

Since the completion of the Human Genome Project, which mapped the human genetic structure, researchers have been looking for gene variants that are linked to specific disorders or which work together with other factors to cause disease. Spooner said that Y1102 is one of the first to come from the gene mapping project.

Eventually, said Spooner, doctors will be able to use such gene variants to individualize medical care. This means the physician could tailor treatments, prevention advice and drug dosages specifically for a patient based on the group of gene types that individual may have. Such a targeted treatment could help a patient avoid harmful side effects common to some drugs. If a patient is genetically susceptible to a disorder, knowing in advance may prompt lifestyle or diet changes that would prevent the disease from ever developing.

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