According to this classification, there are three types of adult-type diffuse gliomas, namely astrocytoma (isocitrate dehydrogenase-IDH-mutant, grades 2–4), oligodendroglioma (IDH-mutant, 1p/19q-codeleted, grades 2–3), and glioblastoma (IDH-wild-type, grade 4). The gene discussed is IDH2; the disease is oligodendroglioma.