Were you looking instead for APOE genotyping ordered to evaluate for Alzheimer disease? If so, see APOE Genotyping, Alzheimer Disease.
At a Glance
Why Get Tested?
APOE genotype tests are most often done as part of research protocols to help understand the role of genetic factors in cardiovascular disease. However, the testing is sometimes used in clinical settings to help confirm a diagnosis of type III hyperlipoproteinemia (also known as familial dysbetalipoproteinemia).
When to Get Tested?
A blood sample drawn from a vein in your arm
Test Preparation Needed?
The Test Sample
What is being tested?
Apolipoprotein E (Apo E) is a protein that helps transport lipids (fats and cholesterol) in the blood. It is recognized by specific cell surface receptors that allow it to deliver lipids to cells for use or storage and to deliver excess lipid to the liver for excretion.
The ApoE protein has three genetic forms that have slightly different compositions. They are called ApoE2, ApoE3, and ApoE 4. ApoE2 is poorly recognized by cell surface receptors whereas ApoE3 and ApoE4 bind tightly to those receptors. Therefore, people with ApoE2 tend to have higher blood lipids since delivery from blood to cells is impaired by poor binding of ApoE2 to receptors.
Three different genes (termed alleles) are designated as e2, e3, and e4 and code respectively for ApoE2, ApoE3, and ApoE4. Each person inherits one allele from each parent. A person who has the same allele from each parent is termed homozygous: e2/e2 or e3/e3 or e4/e4. One who has different alleles is termed heterozygous: e2/e3 or e2/e4 or e3/e4.
APOE e3/e3 is the most common genotype (seen in about 63% of the population) and is considered "neutral." Risks of disease are made relative to the e3/e3 population.
APOE e4 (as e4/e4 and e4/e3) is found in 25% of the population and is associated with an increased risk of atherosclerosis. People with these genotypes could be predisposed to a significantly elevated level of LDL-C ("bad cholesterol") and triglycerides when their diet is high in saturated fat.
People with the APOE e2 allele tend to have lower LDL-C levels but elevated triglycerides. APOE e2 is also associated with type III hyperlipoproteinemia/hyperlipidemia (HPL III or familial dysbetalipoproteinemia), a rare inherited disorder that causes fatty yellowish deposits on the skin called xanthomas, increased triglycerides in the blood, and atherosclerosis that develops at an early age. However, only about 2% of people with the e2/e2 genotype develop type III hyperlipoproteinemia/hyperlipidemia.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
Sources Used in Current Review
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(2013) Yan-Wei Yin, et al. Association between Apolipoprotein E Gene Polymorphism and the Risk of Coronary Artery Disease in Chinese Population: Evidence from a Meta-Analysis of 40 Studies. PLoS ONE 8(6): e66924. doi:10.1371/journal.pone.0066924. Available online at http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0066924 through http://www.plosone.org. Accessed October 2013.
Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. McPherson R, Pincus M, eds. Philadelphia, PA: Saunders Elsevier: 2011, 230-231.
(December 2, 2010) Citkowitz E. Dysbetalipoproteinemia Workup. Medscape Reference. Available online at http://emedicine.medscape.com/article/118466-workup through http://emedicine.medscape.com. Accessed October 2013.
(2007) Bennet A, et al. Association of apolipoprotein E genotypes with lipid levels and coronary risk. JAMA 2007; 298(11):1300. Abstract available online at http://www.ncbi.nlm.nih.gov/pubmed/17878422 through http://www.ncbi.nlm.nih.gov. Accessed October 2013.
(2008) Donnelly L, et al. Apolipoprotein E genotypes are associated with lipid lowering responses to statin treatment in diabetes: a Go-DARTS study. Pharmacogenet Genomics 2008; 18(4):279. Abstract available online at http://www.ncbi.nlm.nih.gov/pubmed/18334912 through http://www.ncbi.nlm.nih.gov. Accessed October 2013.
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