Diagnostic approaches to Alzheimer's disease.

The importance of obtaining an accurate and early diagnosis for Alzheimer's disease is now becoming recognized. Nonpharmacological as well as pharmacological therapies can be best initiated once a diagnosis is obtained. Biochemical markers to identify Alzheimer's disease have been sought for many years, with many candidates proposed. Recently criteria were established to evaluate putative diagnostic tests. Several biomarkers now show utility in identifying those with Alzheimer's disease. The ApoE e4 allele, while a risk factor rather than a deterministic gene, in the context of an individual with suspicion of AD has a positive predictive value of 94-98% and may come to have utility in predicting response to certain classes of pharmacological agents. Independent groups have shown that the markers in cerebrospinal fluid tau and Ab42 are, respectively, elevated and reduced in patients with AD versus other patient groups and that the lumbar puncture itself is usually well tolerated. For early-onset AD, sequencing presenilin 1 has come into use and the positive frequency is similar to that found in other genetic-based laboratory tests.