DALLAS, October 6 -- While experts agree that genetic testing has helped identify people who may not appear to be at high risk for genetic forms of heart disease, testing most frequently serves to confirm traditional diagnostic methods, according to a new American Heart Association scientific statement. In most instances, cardiologists still depend on traditional means of diagnosis, including non-invasive testing, say the authors in their statement published in today's Circulation: Journal of the American Heart Association.
However, the public is becoming more interested in the link between genes and diseases, says the statement's co-author James Moller, M.D., a Paul Dwan Professor of pediatric cardiology at the University of Minnesota, Minneapolis and Fairview-University Medical Center.
"We see and hear a lot about genetic findings in the news, and people are asking their physicians questions," says Moller, a past president of the AHA. "This report explores the accuracy and usefulness of DNA testing on three major inherited heart-related disorders: hypertrophic cardiomyopathy (HCM), long QT-Syndrome (LQTS), and Marfan Syndrome (MFS)."
The panel, which prepared the statement, also considered societal issues such as employment and insurance discrimination and privacy concerns. According to Moller, the panel's major findings were two-fold. "Some of these diseases have clear-cut clinical features, and you do not need genetic tests to define them," he says. "In others, such as LQTS, the genetic background has not been worked out. Although gene tests can be helpful, a lot of these genes have not been completely defined. We still need to work out more fundamental knowledge."
HCM is a heart defect found in about 1 in 500 persons. It can appear at any stage in life. However, premature death often occurs suddenly. The disease is characterized by increased thickness of the wall of the left ventricle, the largest of the four chambers of the heart.
LQTS is less common and genetically predisposes individuals to fainting spells and sudden cardiac death, typically due to irregular heartbeats brought on by stress or vigorous activity. LQTS is often symptomless and undiagnosed but is acknowledged as a cause of sudden cardiac death in young, apparently healthy people -- notably competitive athletes.
The authors say there are several of difficulties in diagnosing LQTS using conventional methods, which lead to uncertain diagnoses in as many as 50 percent of cases. Thus, they say a genetic diagnosis would give the most accurate information, especially for people who physicians classify as "borderline." MFS is a disease of the connective tissues affecting about 40,000 Americans. People with this defect have a 50-50 chance of passing the condition on to their children. Because the disease principally affects the eyes and bones as well as the cardiovascular system, physicians use physical appearance and clinical tests as the primary means of diagnosis. Not all MFS patients show classic features of the disease and many of these abnormalities appear in the general population, which complicates clinical diagnosis. While diagnostic criteria for MFS are well established, there are many gene mutations associated with the disorder. Therefore, routine molecular screening cannot be used by itself. Genetic testing for MFS can only be regarded as a confirmation of a doctor's office diagnosis, the statement concludes.
"The question the panel was asking was, 'To what extent has laboratory genetic testing changed the landscape of cardiovascular diagnosis?'," says the statement's lead author, Barry Maron, M.D., panel chairman and director of cardiovascular research at the Minnesota Heart Institute Foundation, Minneapolis. "The answer we found was that it hasn't changed things completely and we do still rely on traditional testing. But genetic testing's role has been very important in identifying certain subgroups."
The authors say that access to genetic diagnosis is limited and commercial or governmental involvement will be necessary for widespread DNA diagnosis of cardiovascular diseases. "This statement puts matters into perspective with regard to clinical and molecular diagnoses at this time, and argues that the importance of a doctor's office diagnosis has not been diminished," says Maron. "While molecular diagnosis is not yet widely available, the research tool of DNA diagnosis has already taught us a great deal."
The statement's co-authors are Christine E. Seidman, M.D.; G. Michael Vincent, M.D.; Harry C. Dietz, M.D.; Arthur J. Moss, M.D.; Jeffrey A. Towbin, M.D.; Henry M. Sondheimer, M.D.; Reed E. Pyeritz, M.D., Ph.D.; Glenn McGee, Ph.D.; and Andrew E. Epstein, M.D. All are from the Councils on Clinical Cardiology, Cardiovascular Disease in the Young, and Basic Science, American Heart Association.