WASHINGTON (AP) - In a study that could lead to new treatment for congestive heart failure, researchers have shown that an abnormal form of a protein can be a fundamental cause.
Earlier studies in animals had suggested that the protein phospholamban, or PLN, played a key role. Now, by studying four generations of a family in which the heart disease was common, researchers have shown that an abnormal form of the protein molecule was the primary cause.
Dr. Christine E. Seidman, a researcher at the Howard Hughes Medical Institute and Harvard Medical School, said the abnormal PLN disrupts the calcium cycle in heart muscle and causes the heart to lose its ability to efficiently pump blood.
Calcium causes heart muscles to contract and PLN then helps move the calcium away so that the muscles can relax between beats. This action, called a calcium pump, is essential for the proper beating of the heart.
Seidman, co-author of a study appearing Friday in the journal Science, said her study shows that a gene mutation produces an abnormal form of PLN which, in turn, disrupts the calcium pump and causes congestive heart failure.
Both Seidman and another doctor who has done research with animals said the discovery may now make it possible to develop a drug that specifically controls the action of PLN or the movement in and out of the muscles of calcium.
Congestive heart failure occurs when infection, heart attack or high blood pressure weakens the heart muscle, lowering its ability to contract and force blood to the lungs and to the rest of the body. The often-fatal disorder affects about 4.7 million Americans, most of them elderly, and costs about $17.8 billion a year for treatment and care.
In some families an inherited condition can cause heart failure to start before the age of 30.
"This particular gene mutation ... alters the protein in a subtle way," said Seidman. "We have shown that this causes heart failure."
She said the study shows that when the function of PLN is altered, "you get heart failure. No other part of the heart has gone awry."
Seidman and her co-authors found the mutation by analyzing the genes in a four generations of a family where heart failure at an early age was common.
"These individuals all have normal hearts," she said. "They don't have underlying coronary artery disease. But through a fluke of nature they have a subtle change in this protein so that calcium is not regulated in the heart. That causes them to get heart failure."
Dr. Kenneth R. Chien, a heart researcher at the University of California, San Diego school of medicine, said he and others have shown in animal studies that manipulating phospholamban can cause heart failure, but the new study is the first to show that PLN causes the disease in humans by altering the flow of calcium in and out of heart muscle.
"What this rare form of heart failure tells us is that we need to treat abnormal calcium handling and that it is contributing to heart failure," he said.
Seidman and her group found the role of PLN in heart failure by studying 30 members in four generations of a family. The study found that in the 13 family members with early heart failure, there was a subtle change in the PLN gene. This change caused PLN to dampen the action of the calcium pump in the heart muscle and disrupt the proper cycling of calcium. As a result, the muscles lost their efficiency and the heart quickly weakened, she said.
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