WASHINGTON (AP) - A gene variation found in about 13 percent of black Americans greatly increases the risk of irregular heartbeat, a condition linked to the sudden death of about 450,000 people a year in the United States.
To identify the variant, researchers screened hundreds of DNA specimens, searching for different forms of a gene called SCN5A that plays a key role in the chemical and electrical cycling of heartbeat.
They found that the variant, called Y1102, was present in more than half of the black American patients who were being treated for cardiac arrhythmias, or irregular heartbeats. People with the gene variant have eight times the risk of developing a rare type of heartbeat irregularity. The gene variant was not found in screenings of white and Asian patients and in only one of 123 Hispanic patients tested.
Dr. Mark T. Keating, senior lead author of the study appearing Friday in the journal Science, said the variant has a subtle effect on risk, becoming a concern only when a patient has other conditions that already prompt a tendency toward a type of irregular heartbeat called prolongation of the QT interval.
"For most people, such an arrythmia is not a big deal, but for people who have this allele (gene variation) it is a bigger deal," said Keating. "This allele will not cause arrythmia 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 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.
For patients with the Y1102 variant, Keating said, "It's important to make sure that serum electrolytes stay normal. We do things all the time that make them abnormal, such as taking diuretics (drugs to reduce fluids in the body) or running marathons."
Keating said patients should consider discovery of the gene variant as "good news" because it will give doctors an additional clue about how to treat them. For instance, if a physician knows a patient has the Y1102 variant, he can avoid prescribing medications that might aggravate the tendency toward cardiac arrhythmia.
"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 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.
Finding the Y1102 variant, said Spooner, "is one of the first steps toward such individualized medicine."
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On the Net:
Science: http://www.sciencemag.org
Heart arrhythmias: http://www.nhlbi.nih.gov
