At a Glance
Why Get Tested?
Apo E genotyping is not widely used. The clinical usefulness of this test is still being researched. However, it may be used in two different conditions:
- For cardiovascular risk assessment, to help make treatment decisions for individuals with cardiovascular disease or to help confirm a diagnosis of Type III hyperlipoproteinemia (also known as familial dysbetalipoproteinemia)
- As an aid in the diagnosis of probable late onset Alzheimer's disease in a symptomatic adult
When to Get Tested?
- When your doctor suspects that you have an inherited component to your high cholesterol and triglyceride levels or if you have yellowish lesions called xanthomas on your skin
- When you have progressive symptoms of dementia and your doctor wants to determine the likelihood that this is due to Alzheimer’s disease
A blood sample drawn from a vein in your arm
Test Preparation Needed?
The Test Sample
What is being tested?
Apolipoprotein (Apo) E is produced under the direction of the ApoE gene and is one of five main types of blood lipoproteins (A-E). It is produced primarily in the liver and brain and has two primary metabolic roles:
- The transport of lipids from where they are made or absorbed to the tissues where they are stored.
- The transport of cholesterol and other lipids from the body's organs to the liver for excretion. ApoE also plays a role in lipoprotein metabolism. It helps clear very low-density lipoprotein (VLDL) and chylomicrons, the large lipoproteins that are responsible for the initial transport of dietary lipids to the liver, from the bloodstream.
This test looks at a person's DNA to determine what combination of ApoE forms (genotype) is present. The ApoE gene exists in three different forms (alleles) – e2, e3, and e4 – with e3 being the most common allele, found in 60% of the general population. Everyone inherits a pair of ApoE genes that is some combination of these three.
ApoE e3/e3 is the most common genotype. ApoE e4 (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 an exaggerated elevation of LDL-C ("bad cholesterol") and triglycerides when their diet is high in saturated fat.
ApoE e4 has also been associated with an increased risk of late onset Alzheimer's disease (AD) – AD that develops after the age of 65. This effect is additive in that one copy of e4 (e2/e4 or e3/e4) carries some increased risk and two copies of e4 (e4/e4) are associated with an even greater risk of developing AD. It is important to note, however, that this risk is only relative. Most individuals with ApoE e4 will never develop AD and there are many AD patients who are e4 negative.
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.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in your 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
Pagana, K. D. & Pagana, T. J. (© 2007). Mosby’s Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 110-114.
(Updated 2009 May 9). Alzheimer's Disease Genetics Fact Sheet. Alzheimer’s Disease Education & Referral Center [On-line information]. Available online at http://www.nia.nih.gov/Alzheimers/Publications/geneticsfs.htm through http://www.nia.nih.gov. Accessed May 2009.
Bird, T. (Revised 2008 July 24). Alzheimer Disease Overview. GeneReviews [On-line information]. Available online at http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=gene∂=alzheimer through http://www.ncbi.nlm.nih.gov. Accessed May 2009.
Rogaeva, E. (2009 February 5). The Genetic Profile of Alzheimer's Disease: Updates and Considerations. Medscape from Geriatrics and Aging [On-line information]. Available online at http://www.medscape.com/viewarticle/586756 through http://www.medscape.com. Accessed May 2009.
Gandelman, G. (Updated 2008 January 23). Familial dysbetalipoproteinemia. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/000402.htm. Accessed May 2009.
Mayo Clinic Staff (2008 September 17). Alzheimer's: Is it in your genes? MayoClinic.com [On-line information]. Available online at http://www.mayoclinic.com/print/alzheimers-genes/AZ00047/METHOD=print through http://www.mayoclinic.com. Accessed May 2009.
(Updated 2008 December). Cardiovascular Disease (Non-traditional Risk Markers) - Risk Markers - CVD (Non-traditional). ARUP Consult [On-line information]. Available online at http://www.arupconsult.com/Topics/CardiacDz/CVDRiskMarkerNontrad.html through http://www.arupconsult.com. Accessed May 2009.
(September 18, 2007) Riordan M. Linear association among apoE genotypes with LDL levels and coronary risk. Available online at http://www.theheart.org/article/813529.do through http://www.theheart.org. Accessed July 2009.
Sources Used in Previous Reviews
Thomas, Clayton L., Editor (1997). Taber’s Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].
Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby’s Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.
Sloane, P. (1998, November 1). Advances in the Treatment of Alzheimer’s Disease. American Family Physician by the American Academy of Family Physicians [On-line journal]. Available online at http://www.aafp.org/afp/981101ap/sloane.html through http://www.aafp.org.
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Stephen P. Day, Ph.D. Director, Medical Affairs, Third Wave Molecular Diagnostics.
Robert C. Green, M.D., M.P.H. Professor of Neurology, Genetics and Epidemiology. Director, Alzheimer's Disease Clinical and Research Program. Boston University Schools of Medicine and Public Health, Boston, MA.
Ian R.A. Mackenzie, MD FRCPC. Department of Pathology, Vancouver General Hospital, British Columbia, Canada.