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More than 800 genetic tests, many using DNA-based technology, are currently available or in development. Although most available tests are for rare diseases, tests to identify inherited risk for common diseases such as breast and colorectal cancer, Alzheimer's disease, and coronary heart disease have been developed. Decisions about using these genetic tests should be based on three factors, concludes a group of experts who participated in the Human Genetic Epidemiology Workshop recently convened by the Centers for Disease Control and Prevention.
David Atkins, M.D., of the Agency for Healthcare Research and Quality, and other experts identified these factors as the test's analytic validity (accuracy with which a particular genetic characteristic, for example, a DNA sequence variant, can be identified in a given laboratory test); clinical validity (accuracy with which a test predicts a particular clinical outcome, such as breast or ovarian cancer); and clinical utility (likelihood that it will lead to an improved health outcome).
Assessments of these genetic test qualities will enable policymakers, clinicians, and the public to identify quickly what is known and not known about these genetic test qualities. In this way, uncertainties can be taken into account along with ethical, legal, and social implications when they consider using certain genetic tests. For example, newborn screening for phenylketonuria, a rare genetic condition in which failure to metabolize dietary phenylalanine leads to severe retardation, has high clinical validity and utility. It is reliable and accurate, and there is an effective dietary treatment to prevent mental retardation for those who test positive.
In contrast, the DNA-based test for factor V Leiden, a variant of the gene that codes for a protein involved in clot formation, has limited predictive value and unclear implications for clinical management. Carriers of the gene have a two- to eight-fold increased risk of venous thromboembolism. However, the proposed interventions for patients with factor V Leiden (anticoagulant prophylaxis, avoidance of oral contraceptives) pose potential risks as well as benefits, and none has been systematically studied in such patients.
More details are in "Genetic test evaluation: Information needs of clinicians, policy makers, and the public," by Wylie Burke, M.D., Dr. Atkins, Marta Gwinn, M.D., and others, in the August 15, 2002, American Journal of Epidemiology 156(4), pp. 311-318.
Reprints (AHRQ Publication No. 02-R089) are available from the AHRQ Publications Clearinghouse.
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