At a Glance
Why Get Tested?
When to Get Tested?
When you are an adult who has symptoms of dementia and a strong family history of Alzheimer disease that begins before age 60-65 or if you are an asymptomatic adult with a family member who has early onset Alzheimer disease and an identified PSEN1 genetic mutation
A blood sample drawn from a vein in your arm
Test Preparation Needed?
The Test Sample
What is being tested?
Although most Alzheimer disease (AD) cases start after the age of 65, about 5-10% of cases begin in people younger than 65 years of age. Much of this early onset AD is familial – it runs in family lines and is caused by a genetic mutation. So far, there have been three rare gene mutations that have been identified as being associated with AD3: PSEN1, PSEN2, and amyloid precursor protein (APP).
PSEN1 is the most common of these gene mutations and is thought to cause about 30% to 70% of the cases of AD3. Since PSEN1 is a dominant gene (autosomal dominant), it only takes one mutated copy, inherited from either the mother or father, to lead to the development of AD3.
Why PSEN1 mutations are associated with AD3 is not completely understood. It is thought that the normal role of the PSEN1 gene is to make the presenilin 1, a protein used in the development of the brain and spinal cord. Presenilin 1 also works with other enzymes to cut certain proteins into smaller pieces (amyloid beta peptide). A mutation of PSEN1 produces an abnormal presenilin 1 protein that no longer functions properly, resulting in a breakdown of this process. This breakdown lends itself to increased production of a longer, stickier configuration of the amyloid beta protein, which is toxic to the nervous system and eventually forms the characteristic amyloid plaques seen with AD.
So far, more than 150 mutations of the PSEN1 gene have been identified in a limited number of different family lines worldwide. The large number of mutations suggests that there may be additional mutations not yet known; thus, the PSEN1 test will not identify every person who has a PSEN1 mutation.
The analysis is made easier if a specific PSEN1 mutation has already been identified in a person's family line. The PSEN1 genetic mutation analysis is a relatively new test and is offered by a limited number of laboratories.
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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Bird, T. (Revised 2012 October 18). Early-Onset Familial Alzheimer Disease. NCBI GeneReview [On-line information]. Available online at http://www.ncbi.nlm.nih.gov/books/NBK1236/ through http://www.ncbi.nlm.nih.gov. Accessed March 2014.
Mayo Clinic Staff (2011 March 31) Early-onset Alzheimer's: When symptoms begin before age 65. Mayo Clinic [On-line information]. Available online at http://www.mayoclinic.com/print/alzheimers/AZ00009/METHOD=print through http://www.mayoclinic.com. Accessed March 2014.
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Mayo Clinic Staff (2013 February 9). Alzheimer's genes: Are you at risk? Mayo Clinic http://www.mayoclinic.com/health/alzheimers-genes/AZ00047 through http://www.mayoclinic.com. Accessed March 2014.
Anderson, H. (Updated 2014 March 3). Alzheimer Disease. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/1134817-overview through http://emedicine.medscape.com. Accessed March 2014.
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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.
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Eastman, P. (2002 March). Keeping Alzheimer's at Bay, Early Diagnosis Keeps Patients Functioning Longer. AARP Bulletin Online [On-line serial]. Available online at http://www.aarp.org/bulletin/departments/2002/health/0310_health_1.html through http://www.aarp.org.
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(Reviewed 2008 December). PSEN1. Genetics Home Reference [On-line information]. Available online at http://ghr.nlm.nih.gov/gene=psen1 through http://ghr.nlm.nih.gov. Accessed August 2009.
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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/health/alzheimers-genes/AZ00047 through http://www.mayoclinic.com. Accessed August 2009.