Alzheimer’s disease (AD) is the most common form of dementia in the elderly affecting more that 5 million Americans. It is a progressive neurodegenerative disorder with brain findings of amyloid plaques containing β-amyloid and neurofibrillary tangles. AD is a complex and heterogeneous disease, influenced by many genetic and environmental factors. One of the well characterized genetic factors are mutations in the Apolipoprotein E (APOE) gene.

Apolipoprotein E (APOE) is a member of the apolipoprotein family that plays an important role in lipid metabolism. ApoE protein acts as a lipid carrier as it transports cholesterol from the blood stream to the liver for processing and eventual excretion. In the brain, ApoE protein is mainly produced by astrocytes and transports cholesterol to the neurons. Three allelic variants of APOE defined by two SNPs (rs429358 and rs7412) are associated with increased risk of hyperlipidemia (and therefore development of atherosclerosis and cardiovascular disease) as well as Alzheimer disease. The three variants are ApoE-ε2, ApoE-ε3, and ApoE-ε4.

What does this test tell?

This test is to detect the presence of the APOE4 variant, which is associated with increased risk of late-onset (age >60-65) Alzheimer’s disease (AD). Testing may be considered for patients with dementia to supplement information from clinical and other evaluations. This test is not appropriate for children. APOE genotype results are E2/E2, E2/E3, E2/E4, E3/E3, E3,E4, or E4/E4. APOE genetic testing supplies supplementary information for the clinical diagnosis of Alzheimer’s disease.

Studies have shown that individuals with the ε4 allele present with an increased risk of early and late onset Alzheimer disease as compared to those with the ε2 or ε3 alleles. The occurrence of the ε4 allele in late onset Alzheimer’s patients is as high as 40%.

A hallmark of Alzheimer’s disease is plaque formation due to the deposition of amyloid beta protein. Studies have shown that ApoE binds to soluble Amyloid beta and facilitates its uptake and clearance through cell surface receptors. The metabolism of the Amyloid beta is impacted by the ApoE isoform and the ε4 isoform shows the strongest association with plaque formation.

Genotyping of the APOE gene can support diagnosis of the Alzheimer’s disease in symptomatic individuals but is not sufficient alone to diagnose the disease.

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Sample type:

Mouthwash or saliva sample. Turn-around time 5-10 business days after the sample once the sample is received by the lab.

Limitations:

Analytical validity of the test is available and meets CLIA LDT requirements. Clinical validity is based on literature references. but Results should be interpreted in the light of other considerations such as environmental factors, age, ethnicity, and other health conditions. The results of this test do not diagnose Alzheimer’s disease, nor any other type of dementia. This is not a diagnostic test. This test does not look at all possible genes or variants associated with late- onset Alzheimer’s disease. It reports on the most important known genetic factor associated with early or late-onset Alzheimer’s disease. This test does not look at variants in the APP, PSEN1, PSEN2 genes, which are associated with early-onset Alzheimer’s disease. It does not provide detailed information on other traits associated with APOE variants.

We strongly recommend that you seek genetic counseling to understand the limitations and possible consequences of this test.

 Analytical validity refers to how well the test predicts the presence or absence of a particular gene or genetic change. In other words, can the test accurately detect whether a specific genetic variant is present or absent. Clinical validity refers to how well the genetic variant being analyzed is related to the presence, absence, or risk of a specific disease.

References:

  1. Goldstein, J.L., T. Kita, and M.S. Brown, Defective lipoprotein receptors and atherosclerosis. Lessons from an animal counterpart of familial hypercholesterolemia. N Engl J Med, 1983. 309(5): p. 288-96.
  2. Heeren, J., U. Beisiegel, and T. Grewal, Apolipoprotein E recycling: implications for dyslipidemia and atherosclerosis. Arterioscler Thromb Vasc Biol, 2006. 26(3): p. 442-8.
  3. Bu, G., Apolipoprotein E and its receptors in Alzheimer’s disease: pathways, pathogenesis and therapy. Nat Rev Neurosci, 2009.10(5): p. 333-44.
  4. Chasman, D.I., et al., Qualitative and quantitative effects of APOE genetic variation on plasma C-reactive protein, LDL-cholesterol, and apoE protein. Genes Immun, 2006. 7(3): p. 211-9.
  5. Farrer, L.A., et al., Effects of age, sex, and ethnicity on the association between apolipoprotein E genotype and Alzheimer disease. A meta-analysis. APOE and Alzheimer Disease Meta Analysis Consortium. JAMA, 1997. 278(16): p. 1349-56.
  6. Carter, D.B., The interaction of amyloid-beta with ApoE. Subcell Biochem, 2005. 38: p. 255-72.
  7. Kanekiyo, T., et al., Heparan sulphate proteoglycan and the low-density lipoprotein receptor-related protein 1 constitute major pathways for neuronal amyloid-beta uptake. J Neurosci, 2011. 31(5): p. 1644-51.
  8. Hardy, J. and D.J. Selkoe, The amyloid hypothesis of Alzheimer’s disease: progress and problems on the road to therapeutics. Science, 2002. 297(5580): p. 353-6.
  9. Alzheimer’s, A., 2012 Alzheimer’s disease facts and figures. Alzheimers Dement, 2012. 8(2): p. 131-68.
  10. Cleveland Heart Lab, Apolipoprotein E [PDF File]. Retrieved from http://www.clevelandheartlab.com/wp-content/uploads/2017/01/ApoE-Practitioner-One-Pager-CHL-D023c.pdf

If you have any questions about Alzheimer’s Genetic Testing at Ayass BioScience, LLC, please call today at 972-668-6005 or fill out our contact form on the bottom of this page. We will answer any question you might have.