New gene for heart rhythm abnormality.

An international team of researchers has nabbed the third gene associated with an inherited heart rhythm abnormality that can kill otherwise healthy young people.

About 20,000 people in the United States have the heart arrhythmia known as long QT syndrome, which causes episodes of fast, irregular heartbeats that can lead to fainting and sometimes death. The syndrome gets its name from an abnormally long QT interval-the time between heart contraction and relaxation-on an electrocardiogram.

Last year, geneticist Mark T. Keating, a Howard Hughes Medical Institute investigator at the University of Utah in Salt Lake City, and his colleagues identified two genes, on chromosomes 3 and 7, associated with the syndrome (SN: 3/11/95, p. 149). At the time, they also had evidence that mutations in a third gene, on chromosome 11, accounted for about 55 percent of inherited cases of long QT syndrome.

Keating and his team have now identified the third gene, they report in the January Nature Genetics. All three genes provide blueprints for proteins essential to the heart's rhythmic contractions.

The chromosome 3 gene codes for a sodium channel, a protein needed to spur heart contractions. In contrast, the chromosome 7 gene codes for a potassium channel, required for halting contractions. The newly discovered gene appears to hold the instructions for another potassium channel.

"Essentially, the sodium channel serves as a gas pedal, and the potassium channels serve as the brakes. If either gets out of control, the result can be life-threatening arrhythmias," says Keating. He notes that physicians can identify the gene mutations responsible for long QT syndrome and target treatments specifically to the sodium channel or the potassium channel.

"Understanding long QT syndrome may one day help us treat the more common arrhythmias, which kill 300,000 to 400,000 Americans each year," Keating adds.