IDH1 and glioma: The metabolic hallmark of this glioma subtype is de novo production of high levels of the oncometabolite 2-hydroxyglutarate (2HG), exclusively in the form of the D-enantiomer (D-2HG), by the mutant IDH1 enzyme through the NADPH-dependent reduction of α-ketoglutarate (αKG)4.