The aim of this study was to investigate the dynamics of four of the most 
validated biomarkers for Alzheimer's disease (AD), cerebro-spinal fluid (CSF) 
Abeta 1-42, tau, hippocampal volume, and FDG-PET, in patients at different stage 
of AD. Two hundred twenty-nine cognitively healthy subjects, 154 mild cognitive 
impairment (MCI) patients converted to AD, and 193 (95 early and 98 late) AD 
patients were selected from the Alzheimer's Disease Neuroimaging Initiative 
(ADNI) database. For each biomarker, individual values were Z-transformed and 
plotted against ADAS-cog scores, and sigmoid and linear fits were compared. For 
most biomarkers the sigmoid model fitted data significantly better than the 
linear model. Abeta 1-42 time course followed a steep curve, stabilizing early 
in the disease course. CSF tau and hippocampal volume changed later showing 
similar monotonous trends, reflecting disease progression. Hippocampal loss 
trend was steeper and occurred earlier in time in APOE epsilon4 carriers than in 
non-carriers. FDG-PET started changing early in time and likely followed a 
linear decline. In conclusion, this study provides the first evidence in favor 
of the dynamic biomarker model which has recently been proposed.