Heterozygous point mutations in the active site arginine residues of IDH1 (R132) and IDH2 (R140 and R172) are observed in cancers including low-grade gliomas, secondary glioblastomas, acute myeloid leukemia (AML), angioimmunoblastic T-cell lymphomas, myelodysplastic syndrome (MDS), etc. 2–6. The gene discussed is IDH2; the disease is cancer.