PER2 and leukemia: Furthermore, we currently lack an understanding of how the oscillation of clock genes is altered in both acute and chronic forms of leukemia and what role if any sirtuin (Sirt1) has in regulating the circadian clock in leukemia given that Sirt1, an NAD(+) – dependent protein deacetylase, has previously been shown to regulate circadian clock gene expression in other cellular systems by directly binding to CLOCK-BMAL1, which in turn promotes both the de-acetylation and degradation of Per2 [12].