Subjects with mild cognitive impairment (MCI) are at a high risk of developing 
clinical Alzheimer's disease (AD). We asked to what extent the core biomarker 
candidates cerebro-spinal fluid (CSF) beta-amyloid(1-42) (Abeta(1-42)) and CSF 
tau protein concentrations predict conversion from MCI to AD. We studied 52 
patients with MCI, 93 AD patients, and 10 healthy controls (HC). The MCI group 
was composed of 29 patients who had converted to AD during follow-up, and of 23 
patients who showed no cognitive decline. CSF Abeta(1-42) and tau protein levels 
were assessed at baseline in all subjects, using enzyme-linked immunosorbent 
assays. For assessment of sensitivity and specificity, we used independently 
established reference values for CSF Abeta(1-42) and CSF tau. The levels of CSF 
tau were increased, whereas levels of Abeta(1-42) were decreased in MCI 
subjects. Abeta(1-42) predicted AD in converted MCI with a sensitivity of 59% 
and a specificity of 100% compared to HC. Tau yielded a greater sensitivity of 
83% and a specificity of 90%. In a multiple Cox regression analysis within the 
MCI group, low baseline levels of Abeta(1-42), but not other predictor variables 
(tau protein, gender, age, apolipoprotein E epsilon4 carrier status, Mini Mental 
Status Examination score, observation time, antidementia therapy), correlated 
with conversion status (P<0.05). Our findings support the notion that CSF tau 
and Abeta(1-42) may be useful biomarkers in the early identification of AD in 
MCI subjects.