How SIRT6 mediates its effect on aging or is involved in MDD is not clear, but its functions as an HDAC (Michishita et al., 2008; Kawahara et al., 2009; Tennen et al., 2011) and in DNA repair (Mao et al., 2011) suggest that it may contribute to protecting against aging and psychiatric illness by maintaining telomere integrity or protecting against and repairing the effects of oxidative stress. This evidence concerns the gene SIRT6 and major depressive disorder.