The fifth edition of the WHO Classification of Tumors of the Central Nervous System divides adult-type gliomas into three subtypes based on molecular markers: (1) astrocytoma, isocitrate dehydrogenase (IDH) -mutant, (2) oligodendroglioma, IDH-mutant, and 1p/19q-codeleted, and (3) glioblastoma, IDH-wildtype [2]. The gene discussed is IDH1; the disease is astrocytoma (excluding glioblastoma).