Researchers at Baylor College of Medicine, the Texas Heart Institute and Texas Children's Hospital in Houston have identified a defect in a structural protein that's responsible for a quarter of those who have a hereditary heart problem called Long QT syndrome, a silent killer whose first symptom may be death. They reported their finding in the current issue of Circulation: Arrhythmia and Electrophysiology.

They identified a mutation in a cytoskeletal protein called alpha-1-synotrophin, one of the molecules that helps heart cells maintain shape. The mutation alters how a tiny pore called a sodium ion channel functions, resulting in the syndrome in at least some of the patients for whom the cause was previously unknown.

The researchers explain that ions are charged chemicals, such as sodium or potassium, that move in and out of the channels in the cell membranes, which open and close in a sequence that prompts the cells to beat in unison to pump blood. When the channels are defective, it alters the heart beat, often with devastating effect. When they couldn't find a defect in some of the ion channels, they looked at the proteins that interact with them.

The study included researchers, as well, from St. Luke's Episcopal Hospital in Houston, the Mayo Clinic in Rochester, Minn., and The University of Rochester Medical Center in New York.