The mutant (mt) IDH enzyme catalyses the reduction of α-ketoglutarate (α-KG) to D-2-hydroxyglutarate (2-HG), an oncometabolite affecting the activity of α-KG–dependent dioxygenases6: these events affect a number of cellular responses, and have been shown to induce CpG island DNA hypermethylation in low-grade gliomas (LGGs)7, CCs5 and AMLs8 harbouring IDH1 and IDH2 mutations. The gene discussed is IDH2; the disease is low grade glioma.