APOLIPOPROTEIN E (APOE) GENOTYPING
Label Name: APOE GENO
Lab Discipline: Molecular Diagnostics
Institution:  Duke University Health System 
EAP ID:  LAB6061 
Last Review:  3/17/2017 9:58:24 AM
Specimen Type
  Whole Blood (EDTA)
Container & Volume
  Age Group   Container   Volume  
  0  - 18 Years LAVENDER TOP TUBE 1  ML
Collection Notes
  All:
  • Peripheral Blood: One lavender-top EDTA tube (minimum of 3 mls) is required for testing. Forward unprocessed peripheral blood promptly to the laboratory at ambient temperatures. THE SPECIMEN CANNOT BE FROZEN. GREEN-TOP (HEPARIN) TUBES ARE NOT ACCEPTABLE FOR TESTING.
 
Turn Around Time -  Routine: 10 days   Stat: N/A
Reference Values
APOE GENO
Methodology
  The region of the APOE gene which encompasses the single nucleotide polymorphisms of interest [Rs7412 (c.526C>T, p.Arg176Cys) and Rs429358 (c.388T>C, p.Cys130Arg)] is amplified by PCR using purified genomic DNA as the template. The resulting PCR product is digested using the restriction enzyme CfoI. The digested PCR products are resolved by high resolution capillary electrophoresis to analyze resulting fragment sizes and determine corresponding genotypes.
 
This test was developed and its performance characteristics determined by the DUHS Clinical Molecular Diagnostics Laboratory. It has not been cleared or approved by the U.S. Food and Drug Administration. This test is used for clinical purposes. It should not be regarded as investigational or for research. This laboratory is certified under the Clinical Laboratory Improvement Amendments of 1988 ("CLIA") as qualified to perform high complexity clinical testing.
   
Special Information
  All:
  • Additional Patient Information Required: Due to the unique nature of genetic susceptibility testing, patients offered this test should receive pre-test and post-test genetic counseling. Counseling should help the patient understand the strengths and limitations of DNA testing and the medical implications for the patient as well as for other family members.
 
   
Clinical Significance and Interpretive Data
    Apolipoprotein E (APOE) is a protein involved in the metabolism of lipids through its action as a constituent of the chylomicron and intermediate density lipoprotein complexes (IDLs). APOE has three major alleles (APOE*2, APOE*3 and APOE*4) coresponding to the three major APOE isoforms (E2, E3 and E4). These are determined by polymorphisms in codon 130 and 176. In an individual patient with two APOE alleles, six possible genotypes are commonly seen: *2/*2, *2/*3, *2/*4, *3/*3, *3/*4 and *4/*4. APOE *3/*3 (E3/E3) is the most common genotype and is found in 60% of the general population.

Individuals who are homozygous for the APOE*2 allele (E2/E2) have an increased risk of developing Type III hyperlipidemia, a rare genetic disease associated with accelerated atherosclerosis and elevated serum cholesterol and triglycerides. Most patients (80-90%) with Type III hyperlipidemia are homozygous for the APOE*2 allele. However, most individuals (>95%) who are homozygous for the APOE*2 allele will never develop this disease. Thus, the APOE genotype influences the development or clinical manifestation of type III hyperlipidemia, but is not the sole contributor. Many studies have investigated the impact of the APOE genotype in non-E2/E2 patients on triglyceride levels, cholesterol levels, vascular disease risk, and coronary heart disease risk. These studies find that many things contribute to these processes including the APOE genotype. However, compared to these other factors, the APOE genotype is not considered a major contributor to risk.

The APOE*4 allele (E4) is associated with an increased risk of developing late onset Alzheimer's disease (AD). Individuals who are homozygous for the APOE*4 allele (E4/E4) have a higher risk than individuals with one APOE*4 allele (heterozygotes). APOE*4 is a risk factor for AD rather than a disease-causing polymorphism. The presence of the APOE*4 allele is not diagnostic of AD, and should not be used to screen asymptomatic patients or their family members. Many individuals with an APOE*4 allele will never develop AD. Furthermore, even in symptomatic patients, only about 60% of those with late onset AD will have an APOE*4 allele. Individuals with early onset AD may benefit from additional or alternative genetic testing. Please contact the DUHS Clinical Molecular Diagnostics Laboratory for additional information or help interpreting the results of this testing.

Reference:

Eichner et al. Apolipoprotein E Polymorphism and Cardiovascular Disease: a Huge Review. American Journal of Epidemiology. 2002; 155(6):487-495

Goldman JS et al. American College of Medical Genetics and the National Society of Genetic Counselors. Genetic counseling and testing for Alzheimer disease: joint practice guidelines of the American College of Medical Genetics and the National Society of Genetic Counselors. Genet Med. 2011; 13(6): 597-605.

Mayeux et al. Utility of the Apolipoprotein E Genotype in the Diagnosis of Alzheimer’s disease. NEJM. 1998; 338(8):506-511.
   
Indications
    ApoE genotyping is RECOMMENDED in patients with:

• A clinical suspicion of Type III hyperlipidemia with symptoms including significantly elevated cholesterol and triglyceride levels that do not respond to life style changes, xanthomas, and premature atherosclerotic vascular disease.

ApoE genotyping MAY BE INDICATED:

• As an adjunct test to increase the specificity of a clinical diagnosis of late onset Alzheimer’s disease in a patient with progressive dementia.
   
Contraindications
    • ApoE genotyping should NOT be used as a screening tool in asymptomatic patients to determine Alzheimer's disease risk.

• ApoE genotyping should NOT be used as a screening tool in individuals with a first degree relative with late onset Alzheimer's disease.
   
Limitations
    • The different ApoE alleles are risk factors for developing disease (Alzheimer’s disease and type III hyperlipidemia). They are NOT disease causing mutations. The sensitivity or specificity of an ApoE genotype for any particular disease is low.

• This test is subject to interference by various factors including PCR inhibitors, poor DNA quality and insufficient DNA quantity. These sources of interference usually produce an uninterpretable result rather and an inaccurate result. Although rare, mutations or polymorphisms occurring in the primer or probe binding regions can affect testing and could produce an inaccurate genotyping result.

• Several studies have investigated the impact of the APOE genotype in non-E2/E2 patients on triglyceride levels, cholesterol levels, vascular disease risk, and coronary heart disease risk. These studies find that many factors contribute to these processes including the APOE genotype. However, compared to these other factors, the APOE genotype is not considered a major contributor to risk (see reference). Thus, these results should be interpreted in conjunction with other clinical or laboratory findings. They are not intended to be used as the sole criteria for patient diagnosis or management decisions and are not a substitute for a physician's judgment and clinical experience.

• The presence of the APOE*4 allele is not diagnostic of AD, and should not be used to screen asymptomatic patients or their family members. Many individuals with an APOE*4 allele will never develop AD. Furthermore, even in symptomatic patients, only about 60% of those with late onset AD will have an APOE*4 allele (see reference). Thus, these results should be interpreted in conjunction with other clinical or laboratory findings. They are not intended to be used as the sole criteria for patient diagnosis or management decisions and are not a substitute for a physician's judgment and clinical experience.
   
Molecular Diagnostics Laboratory
(MDX)

Medical Director:
 Michael Datto, M.D., Ph.D.
 Phone: 919-684-6965
 Email: michael.datto@duke.edu
Lab Director:
 Catherine Rehder Ph.D, FACMG
 Phone: 919-613-8434
 Email: catherine.rehder@duke.edu
Lab Director:
 Siby Sebastian Ph.D., DABMG
 Phone: 919-613-8432
 Email: siby.s@duke.edu

Address: 
 Wadsworth Bldg, Cytogenetics, Rm 0220
 2351 Erwin Rd
 Durham,  NC  27705
 Phone: 919-684-2698
 FAX: 919-668-5424

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