Single gene disorder occurs as the result of a single

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Single-gene disorder: Occurs as the result of a single mutated gene; is inherited in well-described ways Polygenic disorder: Occurs as the result of combined action of more than one gene; is not inherited in simple Mendelian patterns Background: Genetic Tests (2 of 2) Jonas DE, Wilt TJ, Taylor BC, et al. Challenges in and principles for conducting systematic reviews of genetic tests used as predictive indicators. In: Methods guide for medical test reviews. Available at .
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Background on Genetic Tests Challenges in Reviews of Genetic Tests Principles for Addressing the Challenges Illustrative Examples General Overview: Section 2 Jonas DE, Wilt TJ, Taylor BC, et al. Challenges in and principles for conducting systematic reviews of genetic tests used as predictive indicators. In: Methods guide for medical test reviews. Available at .
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Penetrance Penetrance is the proportion of people with a particular genetic change who exhibit signs and symptoms of a disorder. It is essential in determining the future risk of developing a disease and for assessing clinical utility of genetic tests. Sufficient data may be lacking to estimate penetrance. Challenges in Reviews of Genetic Tests (1 of 6) Jonas DE, Wilt TJ, Taylor BC, et al. Challenges in and principles for conducting systematic reviews of genetic tests used as predictive indicators. In: Methods guide for medical test reviews. Available at . Lister Hill National Center for Biomedical Communications. Genetics Home Reference: What are reduced penetrance and variable expressivity. Available at .
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Variable Expressivity Variable expressivity is the range of severity of symptoms among different people with the same condition. Example: Hemochromatosis manifests into a wide spectrum of symptoms that vary in severity from mild to life threatening. The degree of expressivity should be considered in evaluating genetic tests. Challenges in Reviews of Genetic Tests (2 of 6) Jonas DE, Wilt TJ, Taylor BC, et al. Challenges in and principles for conducting systematic reviews of genetic tests used as predictive indicators. In: Methods guide for medical test reviews. Available at . Lister Hill National Center for Biomedical Communications. Genetics Home Reference: What are reduced penetrance and variable expressivity. Available at .
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Pleiotropy This term refers to a single gene’ s influence on multiple phenotypic traits. For example, the genetic mutation causing Marfan’ s syndrome results in cardiovascular, skeletal, and ophthalmologic abnormalities.
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