IDH1 and central nervous system cancer: Interestingly, the frequency of IDH1 mutations present in patients appears inversely related to D2HG levels quantified in glioma tissue, with R132G IDH1 mutations leading to the highest concentrations of D2HG in tumors, followed by R132C and R132H, and mutation frequency trends of R132H > R132C > R132G IDH1 in glioma patients [12,70].