The IDH1 gene encoding the cytoplasmic NADP+-dependent isocitrate dehydrogenase—and more rarely IDH2, encoding the mitochondrial isoform—are frequently mutated in gliomas, especially low grade gliomas and secondary glioblastomas [1]. IDH1/IDH2 mutation is associated with better clinical outcome, whatever the grade, but it is still not clear whether it is merely a prognostic marker or a predictor of the response to radiotherapy or chemotherapy [2–6]. The gene discussed is IDH1; the disease is glioma.