Biological markers and diagnostic investigations in Alzheimer's disease

The diagnosis of Alzheimer's disease (AD) is based on numerous clinical, neuroradiological, neurophysiological, and neuropsychological evaluations, but a definitive diagnosis can only be established at autopsy or by brain biopsy. Because the need for a simple and accurate diagnostic marker is increasing as new drug treatments emerge, intensive research to identify diagnostic markers is now in progress. Computer tomography and magnetic resonance imaging are being used to compare linear and volumetric measurements of brains for patients with AD and normal controls. Functional imaging techniques, such as single photon emission computer tomography and positron emission tomography, are being used to identify possible disease-related changes in regional blood flow, glucose metabolism, and receptor activities. Elevated tau-protein concentrations or reduced levels of beta-amyloid precursor protein in the cerebrospinal fluid; mutations on chromosomes 14, 19, and 21; the presence of the Apo-epsilon-4 allele; and impaired odor identification are also being evaluated as possible markers.