Specific cancer cells, notably grade II/III glioma (35, 36), secondary glioblastoma (127), and acute myeloid leukemia (AML) (16, 60, 103, 144) cells, exhibit heterozygous point mutations in the active sites of cytosolic isocitrate dehydrogenase isoform 1 (IDH1) (8, 11) or isoform 2 (IDH2), localized in the mitochondrial matrix (65, 189). The gene discussed is IDH2; the disease is glioblastoma.