SIRT6 and Alzheimer disease: Importantly, SIRT6 expression is significantly reduced at the protein level in AD brains (n = 7) compared to controls (n = 7) [179,180]; at the mRNA level, decreases in SIRT6 expression are associated with AD progression from Braak stage iii (n = 11) to v (n = 11) or vi (n = 23) [179].