Neurochemical diagnosis of Alzheimer’s dementia by CSF Aβ42, Aβ42/Aβ40 ratio and total tau

Cerebrospinal fluid (CSF) concentrations of amyloid β peptides ending at positions 42 and 40 (Aβ42 and Aβ40, respectively), and total tau (tTau) protein were measured by ELISA in order to compare their accuracy in discriminating patients with Alzheimer's disease (AD, n=22), non-Alzheimer dementia (nAD, n=11) and control subjects (CON, n=35). As compared to the other groups, the concentrations of Aβ42 and tTau were decreased (P<0.001) and increased (P<0.001) in AD, respectively, while Aβ40 did not differ significantly among the groups. Receiver operating characteristic (ROC) analysis was performed to define cut-off values for maximized sensitivity and specificity. For all groups compared the Aβ peptide ratio 42/40 classified more patients correctly, as compared to the concentration of Aβ42 alone: AD versus controls, 94 and 86.7%; AD versus nAD, 90 and 85% and AD versus nAD plus controls, 90.8 and 87%, respectively. The percentage of correctly classified patients was further improved when the Aβ ratio was combined with the analysis of the tTau concentration. Presence of the apolipoprotein E ε4 allele, age or degree of mental disability did not significantly influence the parameters studied.