In GBM, neomorphic IDH1/2 mutations lead to the conversion of α-KG into the oncometabolite D-2-hydroxyglutarate (D-2-HG), which acts as an antagonist of α-KG, inhibiting the activity of α-KG-dependent dioxygenases [136, 137]. The gene discussed is IDH1; the disease is glioblastoma.