APOE genotyping is sometimes used as an adjunct test to help in the diagnosis of probable late onset Alzheimer disease (AD) in symptomatic adults. It is called susceptibility or risk factor testing because it indicates whether there is an increased risk of AD but is not specifically diagnostic of AD. If a person has dementia, the presence of APOE e4 may increase the likelihood that the dementia is due to AD but does not prove that it is.
There are no clear-cut tests to diagnose Alzheimer disease during life. Health practitioners can, however, make a reasonably accurate clinical diagnosis of AD by ruling out other potential causes of dementia and checking for a genetic predisposition to AD with APOE genotyping as supplemental information in conjunction with Tau/Aß42 testing.
APOE genotyping may be ordered as an adjunct test when an individual has symptoms of progressive dementia, such as decreasing intellectual ability and language and speech skills, memory loss, and personality and behavioral changes that are starting to interfere with daily living. After non-AD causes, such as overmedication, vascular dementia (caused by strokes), and thyroid disease, have been ruled out, APOE genotyping may help determine the probability that dementia is due to Alzheimer disease.
People who have symptoms of late onset Alzheimer disease (AD) and have one or more APOE e4 copies are more likely to have AD. However, it is not diagnostic of AD and should not be used to screen asymptomatic people or their family members. Many of those who have e4 alleles will never develop AD. Even in symptomatic people, only about 60% of those with late onset AD will have APOE e4 alleles.
Although APOE genotyping is being used clinically by Alzheimer experts, the most it can provide at this time is additional information about a person with dementia. A definite diagnosis of Alzheimer disease can only be made by examining a person's brain tissue after their death.
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.
This article was last reviewed on March 18, 2014. | This article was last modified on March 26, 2014.
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