Somatic mutations of isocitrate dehydrogenase (IDH) 1 and IDH2 were first found in gliomas [3] to convert α-ketoglutarate to oncometabolite R(-)-2-hydroxyglutarate (2-HG), although IDH1 and IDH2, respectively, catalyze the oxidative carboxylation of isocitrate to α-ketoglutarate in cytosol and mitochondria [4]. The gene discussed is IDH3A; the disease is central nervous system cancer.