IDH1 and oligodendroglioma: In fact, the distinction is so dramatic that the new World Health Organization (WHO) scheme has split adult-type infiltrative gliomas into three discrete subsets: “Astrocytoma, IDH1/2mut, WHO grades 2–4,” “Oligodendroglioma, IDH1/2mut and 1p/19q-codeleted, WHO grades 2–3” and “Glioblastoma, IDH1/2wt, WHO grade 4” [6].