In cell culture and AD postmortem tissue, ApoE4 expression is shown to be associated with a decreased level of SIRT1 and increased level of SIRT2 (which is associated with neurodegeneration Liu et al., 2012; Outeiro et al., 2007), resulting in a decrease in SIRT1/SIRT2 ratio (Theendakara et al., 2013). Here, SIRT1 is linked to Alzheimer disease.