IDH1 and glioma: The discovery of IDH1/2 mutations in glioma has fueled the classification of malignant gliomas at the phenotypic, molecular, and genetic levels, ultimately leading to the definition of three major glioma subtypes – mesenchymal, classical, and proneural (Phillips et al., 2006; Verhaak et al., 2010; Louis et al., 2016).