Three types of adult glioma are now recognized: isocitrate dehydrogenase (IDH) wild-type glioblastoma multiforme (GBM), IDH-mutant astrocytoma, and IDH-mutant and 1p/19q-codeleted oligodendroglioma (ODG) [12]. The gene discussed is IDH3A; the disease is oligodendroglioma.