Blacks Suffer Gene Variant, Study Finds

WASHINGTON — The deaths of 450,000 people a year in the United States are linked to irregular heartbeats, and a study has found that 13% 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 today in the journal Science, researchers say they screened hundreds of DNA specimens looking for forms of a gene called SCN5A, which plays a key role in the chemical and electrical cycling of heartbeats.

They found that the variant, Y1102, was present in more than half 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 Latinos tested.

Dr. Mark T. Keating, senior author of the study, said the variant has a subtle effect on risk, becoming a concern only when patients have 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 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, or by medications used to control blood pressure or eliminate excess fluids.

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