Molecular testing of apolipoprotein E polymorphisms is used to test patients with type III hyperlipoproteinemia and to assess the likelihood of developing Alzheimer's disease.
Apolipoprotein E (ApoE) is a component of low-density lipoprotein (LDL) and mediates the transfer of cholesterol from the liver to body tissues. ApoE still participates in numerous functions in addition to lipid metabolism, such as modulating the cellular immune response, inhibiting platelet aggregation, and regulating steroid hormone synthesis. In the peripheral nervous system, ApoE affects the development and differentiation of neurons. As a result of this event and its involvement in the cleavage of neurotoxic amyloid peptides, ApoE has been implicated in the pathogenesis of Alzheimer’s disease.
The ApoE gene is located on chromosome 19 and appears with three relatively common polymorphisms. The most common polymorphism, ApoE3 results in the amino acid cysteine at position 112 and arginine at position 158 of the polypeptide chain. ApoE2 polymorphism contains only cysteine molecules at these sites and ApoE4 polymorphism only arginine molecules. Depending on the combination of polymorphisms, there are six different genotypes.
Compared to the normal ApoE3/E3 genotype, ApoE2 and ApoE4 have less affinity for the LDL receptor, which may lead to hypercholesterolemia and an increased risk for cardiovascular disease.
ApoE4 allele carriers are at increased risk for Alzheimer's disease. Alzheimer's disease is a multifactorial disease and the presence of an ApoE4 allele alone is not sufficient for the onset of the disease. However, knowledge of the ApoE genotype can increase the specificity of clinical diagnosis and thus its utility in the diagnosis of Alzheimer's disease.
Laboratory test results are the most important parameter for the diagnosis and monitoring of all pathological conditions. 70%-80% of diagnostic decisions are based on laboratory tests. The correct interpretation of laboratory results allows a doctor to distinguish "healthy" from "diseased".
Laboratory test results should not be interpreted from the numerical result of a single analysis. Test results should be interpreted in relation to each individual case and family history, clinical findings, and the results of other laboratory tests and information. Your personal physician should explain the importance of your test results.
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