SIRT1 and glioblastoma: While some clinical studies report that majority of gliomas express increased levels of SIRT1 (both mRNA and protein) which are predictive of poor prognosis, as compared to gliomas expressing lower levels of SIRT1.59,60 In contrast, other studies report reduced levels of SIRT1 expression in gliomas,61 that 80% of GBM tumors exhibit a loss of one allele of the gene encoding SIRT1,62 and that decreased levels of SIRT1 (both mRNA and protein) are predictive of poor prognosis, as compared to GBMs with diploid SIRT1, expressing higher levels of SIRT1.