Microglia from older AD model mice have a twofold to sixfold reduction in expression of Aβ-binding receptors SR-A, CD36 and RAGE compared to wild type controls, in addition there was a significant reduction in the expression of secreted Aβ-degrading enzymes IDE, NEP and MMP-9 (Hickman et al., 2008). This evidence concerns the gene MMP9 and Alzheimer disease.