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By PAUL RECER
.c The Associated Press

WASHINGTON (AP) - The sudden deaths of 450,000 people a year in the United States are linked to irregular heart beats, and a new study has found 13 percent of black Americans have a gene variation that greatly increases their risk of developing a rare type of abnormal cardiac rhythm.

In a study appearing Friday in the journal Science, researchers say they screened hundreds of DNA specimens looking for forms of a gene called SCN5A, which has a key role in the chemical and electrical cycling of the heartbeat.

They found the variant, Y1102, was present in more than half of the black patients who were being treated for cardiac arrhythmias, or irregular heartbeats. People carrying the gene variant are eight times more likely to develop a rare type of irregular heartbeat than those who don't.

Researchers did not find the variant in screenings of white and Asian patients. They found it in only one of 123 Hispanic patients tested.

Dr. Mark T. Keating, senior author of the study, said the variant has a subtle effect on risk, becoming a concern only when a patient has other conditions that would make them susceptible to a rare type of irregular heartbeat, known as prolongation of the QT interval.

``For most people, such an arrhythmia is not a big deal, but for people who have this allele (gene variation) it is a bigger deal,'' said Keating, a researcher at the Children's Hospital in Boston and a member of the Harvard Medical School faculty. ``This allele will not cause arrhythmia by itself. You have to have several things go wrong at the same time.''

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 of electrolytes in blood serum.

Electrolytes such as potassium, calcium, sodium and magnesium are chemicals that affect cardiac rhythm, and their levels can be decreased by extreme exercise, medications used to control blood pressure or to eliminate excess fluids.

Patients with the Y1102 variant need to keep serum electrolytes normal, Keating said.

``We do things all the time that make them abnormal, such as taking diuretics (drugs that reduce fluids in the body) or running marathons,'' he said.

The discovery of the gene variant is good news for patients because it will give doctors a better clue of how to treat them, Keating said. For instance, if a physician knows a patient has the variant, he can avoid prescribing medications that might aggravate the tendency toward an irregular heartbeat.

``It is not urgent or feasible today to test for this (gene variant), but eventually genetic testing for things like this will be part of the doctor's tool kit to help prevent or predict illness,'' said Keating.

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 linked to specific disorders or which work together with other factors to cause disease. Spooner said that Y1102 is one of the first variants identified as a result of the project.

Spooner said doctors eventually will be able to use gene variants to customize medical care, meaning a physician could tailor treatments based on the patient's genetic makeup. Such a targeted treatment could help a patient avoid harmful side effects with some drugs. Knowledge about the variant could also help a patient make lifestyle or diet changes that would prevent the disease from ever developing.

Finding the Y1102 variant ``is one of the first steps toward such individualized medicine,'' Spooner said.

On the Net:

Science: www.sciencemag.org

Heart arrhythmias: www.nhlbi.nih.gov


 
08/22/02 14:42 EDT
   
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