Jan. 31, 2002 ROCHESTER, MINN. — United States and German scientists have discovered how a genetic defect causes dilated cardiomyopathy (DCM), a form of heart failure that claims 10,000 American lives each year. The research findings are published in Tuesday's edition of Circulation: Journal of the American Heart Association.
The findings suggest how existing medications could help patients with DCM, a condition in which the heart becomes greatly enlarged and loses its ability to pump blood efficiently.
"We predict that drugs that lower blood pressure and the heart’s overall workload will not only improve symptoms but lessen heart muscle damage in dilated cardiomyopathy patients with this genetic abnormality," says Timothy M. Olson, M.D., a Mayo Clinic cardiovascular disease specialist and one of the study’s two lead authors. "By establishing how the disease develops in these patients, this study provides direction both for improving treatment and long-term research.
"When patients with DCM see their doctors with symptoms of heart failure, heart muscle damage is often extensive, and the only long-term solution may be a transplant," says Dr. Olson. "Through clinical testing of the relatives of patients with the disease, however, we could make an earlier diagnosis and evaluate which patients should consider preventive use of beta blockers or ACE inhibitors."
The study of 350 unrelated patients with dilated cardiomyopathy, conducted in collaboration with the Technical University of Braunschweig and the University of Utah, identified three patients who had distinct defects in the same gene.
The work builds upon research first reported by Mayo Clinic in the early 1990s that showed at least 20 to 30 percent of DCM cases spring from an abnormal gene. While eight other genes associated with DCM have been identified, two of them through research involving Mayo Clinic investigators, the current study is the first to shed light on the mechanism by which a defective gene causes the disease.
Genes are the blueprints the body uses to create proteins, which are the building blocks of muscles. Dr. Olson’s research team found that the defective genes led to errors in the production of a protein called metavinculin that is important in heart muscle cells. The German colleagues used the genes to produce abnormal metavinculin and studied its interaction with other heart-specific proteins. They learned that the abnormal metavinculin disrupted the stability of protein complexes that bind heart muscle cells together. These cells may be more vulnerable to damage under the normal stress of each heartbeat.
Dr. Olson says a patient example from the study provided important confirmation of the laboratory findings and also opened a window to how this discovery could prevent or slow the advancement of the disease.
"One patient received a transplant, and so we were able to examine the structure of the diseased heart. We found irregularities and fragmentation at the interface between muscle cells that is consistent with the disease mechanism identified in the laboratory.
"Relatives of this patient also were screened for the disease. Although none of them had heart failure symptoms, echocardiograms revealed that an aunt had dilated cardiomyopathy and a daughter had a slightly enlarged main pumping chamber. With clinical testing of patients’ relatives, we could identify people at risk and start medication earlier, when it theoretically would do the most good.
"Further study is needed to determine whether this strategy would forestall development of the disease, but based on these findings, clinical screening of relatives and preventive medication seems a prudent approach," says Dr. Olson.
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