Biological and genetic markers of sporadic Alzheimer's disease

With the development of new treatments, there is an increasing need for ear ly diagnosis of sporadic Alzheimer's disease. Therefore, biological markers allowing positive diagnosis early in the course of the disease are highly desirable. Cerebrospinal fluid levels of protein tau were shown to be signi ficantly increased in patients with Alzheimer's disease, Although sensitivi ty is high, poor specificity limits the diagnostic value of this marker. Th e same is true for the 42 amino acid isoform of beta -amyloid protein that is significantly decreased in cerebrospinal fluid of Alzheimer's disease pa tients. However, combining both markers could improve specificity at least allowing differentiation between Alzheimer's disease, normal ageing and dep ressive pseudodementia. Other biological markers such as cerebrospinal flui d levels of neurotransmitters, cytokines or superoxide dismutase were shown to have even less diagnostic value, The apolipoprotein epsilon4 allele is a risk factor for Alzheimer's disease but not a diagnostic marker as many i ndividuals who inherit epsilon4 do not develop the disease. Till now, a sin gle diagnostic marker allowing discrimination between Alzheimer's disease a nd other dementias does not exist. Combined cerebrospinal fluid levels of b eta -amyloid protein and tau protein might be used as a marker that helps d iscriminating Alzheimer's disease from normal ageing and depression.