IDH2 and central nervous system cancer: IDH1/2 mutations identified thus far are heterozygous and produce single amino acid substitutions either at arginine 132 (R132) in IDH1 or arginine 172 (R172) in IDH2 in glioma and leukemia, or at arginine 140 (R140) in IDH2 in AML [19, 21–23].