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Exploring Bioethics - NIH Office of Science Education - National ...

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Alzheimer’s Disease and Genetic Testing: Relevant FactsPart I: APOE in the Human PopulationThe gene for apolipoprotein E (APOE) comes in three varieties (alleles): E2, E3, and E4. While E2protects a person from developing Alzheimer’s disease, E4 increases the chance <strong>of</strong> developing it.Humans inherit one copy <strong>of</strong> the APOE gene from each <strong>of</strong> their biological parents. The APOEgenotype alone does not determine whether a person will develop Alzheimer’s disease, though.About 30 percent <strong>of</strong> Alzheimer’s disease patients have at least one copy <strong>of</strong> E4, but about 30 percent<strong>of</strong> people with the disease do not have a copy <strong>of</strong> E4. So, people without E4 may still get Alzheimer’sdisease, and people with E4 may never get it.Approximate Distribution <strong>of</strong> E2, E3, and E4 in the Human PopulationPercent <strong>of</strong>Human PopulationInheritanceEffect on Person1–2% 2 copies <strong>of</strong> E2 (E2/E2) Decreased chance <strong>of</strong> developingAlzheimer’s disease15% 1 copy <strong>of</strong> E2, 1 copy <strong>of</strong> E3 (E2/E3) Decreased chance <strong>of</strong> developingAlzheimer’s disease55% 2 copies <strong>of</strong> E3 (E3/E3) Normal (baseline) chance <strong>of</strong>developing Alzheimer’s diseaseCopyright © 2009 <strong>Education</strong> Development Center, Inc. <strong>Exploring</strong> <strong>Bioethics</strong>.Permission granted for classroom use.1–2% 1 copy <strong>of</strong> E2, 1 copy <strong>of</strong> E4 (E2/E4) Normal (baseline) chance <strong>of</strong>developing Alzheimer’s disease25% 1 copy <strong>of</strong> E3, 1 copy <strong>of</strong> E4 (E3/E4) 3 to 5 times greater chance <strong>of</strong>developing Alzheimer’s disease1–2% 2 copies <strong>of</strong> E4 (E4/E4) 15 times greater chance <strong>of</strong>developing Alzheimer’s diseaseMaster 4.2 (page 1 <strong>of</strong> 3)

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