While the exact sequence of events tethering decreases in SirT1 to onset of AD symptoms remains unclear, in a first-of-a-kind study Kumar et al. 64 determined there was a decline in serum concentration of SirT1 in healthy individuals with age and, in patients with Mild Cognitive Impairment (MCI) or AD, the decline is even more pronounced and greatest for the latter. Here, SIRT1 is linked to Alzheimer disease.