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The working group sponsored by the Reagan Institute and the National Institute on Aging reviewed published material on Alzheimer's disease and developed the following recommendations through a consensus process. The "Consensus Report of the Working Group on: 'Molecular and Biochemical markers of Alzheimer's Disease'" appears in the April 1998 issue of the journal Neurobiology of Aging.
For early-onset familial Alzheimer's disease, it is appropriate to test for mutations in the presenilin 1, presenilin 2, and amyloid precursor protein genes. These mutations are relatively rare. Only 120 families worldwide are currently known to carry these mutations. Testing should be limited to those with a family history of early-onset Alzheimer's.
In late-onset and sporadic Alzheimer's disease, detecting an e4 allele of the APOE gene can add confidence to the clinical diagnosis.
APOE testing is only appropriate after clinical evaluation yields a likely diagnosis of Alzheimer's. APOE testing cannot be used as a sole diagnostic test, and is not appropriate for asymptomatic individuals.
Among the other proposed molecular and biochemical markers for Alzheimer's disease, none has yet achieved universal acceptance nor fully met the proposed criteria for an ideal biomarker, and thus cannot be accepted for widespread use at present.
These include amyloid deposits in skin (skin test), pupil dilation in response to dilute solution of tropicamide (eyedrop test), neuronal thread proteins in cerebrospinal fluid (AD7C), and serum levels of binding protein p97. Tests of cerebrospinal fluid for abnormal levels of indicator proteins, known as AB42 and tau, come closest to fulfilling the criteria for a useful biomarker.
The ideal biomarker for Alzheimer's disease should have the following qualities: