TUESDAY, Jan. 25, 2005 (HealthDayNews) -- One genetic mutation can cause two kinds of inherited heart problems, a new study claims.
Mayo Clinic researchers have discovered that a mutation in the SCN5A gene, which controls the cardiac sodium channel, can lead to dilated cardiomyopathy (DCM), a type of heart failure, and atrial fibrillation, a type of irregular heartbeat. Their report appears in the Jan. 26 issue of the Journal of the American Medical Association.
"With each heartbeat, electrical signals in the heart are translated into muscle contraction," explained lead researcher Dr. Timothy M. Olson, an assistant professor of medicine and pediatrics from the Mayo Clinic School of Medicine. "This process is initiated by movement of sodium ions into cardiac cells by sodium channels."
"Up to now, inherited forms of mechanical and electrical heart disease were thought to be due to very different types of genes," Olson said. "Our findings show that certain mutations may put individuals at risk for both heart muscle disease and arrhythmias."
The research group found this mutation does not allow a normal amount of sodium ions to reach the heart. Normally functioning sodium channels are essential for the heart to pump effectively.
When enough sodium ions don't get to the heart, the heart muscle becomes enlarged and pumps less strongly. As a result, the muscle of the heart weakens and can't pump blood efficiently throughout the body.
This causes fluid to build up in the lungs, which become congested, making it difficult to breath. This is called left heart failure. There is often right heart failure as well, which causes fluid to build up in the tissues and organs of the body, usually the legs and ankles, and the liver and abdomen. This is DCM.
In addition, the lack of sodium ions makes the heart susceptible to arrhythmias, such as atrial fibrillation.
In their study, Olson's team looked at the genetic profiles of 156 patients with DCM and their families. The researchers found that 27 percent of those with a SCN5A mutation had signs of DCM when they were as young as 20. The average age of diagnosis of DCM among these patients was 27. In addition, 43 percent had atrial fibrillation.
About 20 percent to 30 percent of all heart diseases are hereditary and may be caused by genetic mutations, Olson said. "This gives us a new class of genes that we can look for that may cause DCM," he added.
Olson said it's too early for this finding to have clinical implications, but because mutations in this gene have already been found to cause arrhythmias, people with such arrhythmias should be followed to see if they develop heart failure.
In addition, patients with this gene mutation should not be given sodium channel blockers, because it might make their condition worse, Olson added.
Moreover, "if a patient is diagnosed with DCM or with an arrhythmia that doesn't have a clear basis in traditional risk factors, then they need to consider their family history," Olson said. "In the case of DCM, it is important that their relatives undergo clinical screening to determine whether they, too, are carriers of the disease."
"This is exciting," said Dr. Valentin Fuster, director of the Cardiovascular Institute at Mount Sinai Medical Center. "This discovery genetically links the electrical system with the contractile system of the heart."
For the first time, researchers have shown that a gene affects both the electrical and the mechanical functioning of the heart, explained Fuster, co-author of an accompanying editorial in the journal. "When this gene is altered, both systems get into trouble."
"This is an opening door, not only to a field of investigation of understanding how the heart works," Fuster said, "but is also an opening door that we might understand better disease that before we called idiopathic."
The National Library of Medicine has more on heart failure.