APOE and Alzheimer disease: Among the genes of Group C, we also observed a down-regulation of Apoe. A reduced expression of this gene in the blood of 3xTg-AD mice was already reported [15] and reflects what was observed in AD patients [48,49,50], which was also correlated to a decrease in hippocampal volume [51] and an increase in the amount of cerebral beta amyloid [50,52].