The identification of mutations in two isocitrate dehydrogenase genes, IDH1 and IDH2, in gliomas [1] was a major discovery, leading to a biomarker-defined glioma classification, IDH and ATRX-mutant astrocytomas and glioblastomas and IDH-mutant 1p/19q codeleted oligodendrogliomas [2]. Here, IDH2 is linked to oligodendroglioma.