The 2021 World Health Organization (WHO) CNS classification [2] stratifies adult gliomas into three subtypes based on the mutation status of the isocitrate dehydrogenase 1/2 (IDH1/2) and the co-deletion of the short arm of chromosome 1 (1p) and the long arm of chromosome 19 (19q) (1p/19q co-deletion) into: astrocytoma (AST), IDH-mutant; oligodendroglioma (ODG), IDH-mutant and 1p/19q-codeletion ; and glioblastoma, IDH-wildtype (glioblastoma multiforme; GBM). The gene discussed is IDH1; the disease is oligodendroglioma.