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Screening for Apolipoprotein E (Alzheimer Disease Susceptibility Gene) in Dementia Patients
BACKGROUND: Apolipoprotein E exists as three major isoforms (apoE2, -E3, and -E4), and is coded for by three highly similar alleles. The APOE4 allele has been identified as a risk factor for late onset Alzheimer disease. Numerous case-control and family studies show a calculated overall increased risk of 2.2 - 4.4 fold for heterozygous carriers of one APOE4 gene, and from 5.1 - 17.9 fold in homozygotes (Lancet 347:1091-1095, 1996). Although only a minority of people with dementia apparently have Alzheimer disease, the lifetime risk of AD is 29% for individuals with at least one APOE4 allele, and 9% if no APOE4 is present (Arch Neurol 52:1074-1079, 1995). However, the APOE4 allele is not sufficient to predict AD in asymptomatic individuals, since about half of AD is not APOE4 associated (Ann Neurol 38:797-808, 1995). The primary benefit of this test is for greater certainty in differential diagnosis of AD and not for asymptomatic individuals. Therapies that slow the course of disease such as acetylcholinesterase inhibitors (tacrine, donepezil, and huperzine A) have been approved for the treatment of AD and are most helpful when instituted in the early stages of disease. Recent clinical trials have demonstrated the efficacy of dementia (Asthana et.al. 1997 annual meeting of the Society for Neuroscience) if treatment is instituted in patients with early stage AD. INDICATIONS FOR TESTING:
SAMPLE REQUIREMENTS: Blood: Two 5 ml purple top (EDTA) vacutainers of whole blood inverted several times to mix. Forward within 48 hours at room temperature. INTERPRETATION: PCR based assays are used to detect the three apoE alleles: E2, E3 and E4. COUNSELING ISSUES:
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