Heterozygous mutations in IDH2 at Arg172 and at the analogous residue Arg132 in IDH1 are frequently found in grade 2 and 3 gliomas, secondary glioblastomas, and acute myeloid leukemia (AML [27]), but they occur less frequently in primary glioblastomas and other cancers [28–37]. The gene discussed is IDH1; the disease is acute myeloid leukemia.