While APOE genotyping is mostly done in research settings, it can be used clinically to help in diagnosis and treatment of elevated lipid levels.
APOE testing may be used to help diagnose type III hyperlipoproteinemia (HPL III or familial dysbetalipoproteinemia) in a person with symptoms that suggest the disorder and to evaluate the potential for the condition in other family members. This is a rare inherited disorder that causes fatty, yellowish deposits on the skin called xanthomas, a high level of triglycerides in the blood, and atherosclerosis that develops at an early age.
APOE genotyping has potential to help guide lipid treatment. In cases of high cholesterol and triglyceride levels, statins are usually considered the treatment of choice to decrease the risk of developing cardiovascular disease (CVD). However, there is a wide variability in the response to these lipid-lowering drugs that is in part influenced by the APOE genotype. At present, the clinical utility of this type of information is yet to be totally understood.
APOE e3/e3 is the most common genotype. APOE e3 is associated with "normal" lipid metabolism, thus may not have any genetic impact on risk of developing cardiovascular disease.
APOE e4 (genotype e4/e4 or e4/e3) is found in 25% of the population and is associated with an increased risk ofatherosclerosis. People with these genotypes could be predisposed to significantly elevated levels of LDL-C ("bad cholesterol") and triglycerides when their diet is high in saturated fat.
People with the APOE e2/e2 alleles tend to have lower LDL-C levels but elevated triglycerides. APOE e2 is also associated with type III hyperlipoproteinemia/hyperlipidemia. People with APOE e2/e2 alleles are at a higher risk of premature vascular disease, but they may never develop disease. APOE genotyping adds additional information and, if symptoms are present, e2/e2 can help confirm type III hyperlipoproteinemia.
APOE genotyping is not available in every laboratory. If a health practitioner recommends this test, the specimen will likely be sent to a reference laboratory and results may take longer to return than they would from a local laboratory.
Alterations in lipid concentrations do not lead directly to vascular disease or atherosclerosis. Other factors, such as obesity,diabetes, and hypothyroidism, also play a role in whether a person actually develops disease.