Diffusely infiltrating gliomas (DIGs) are categorized by the World Health Organization (WHO) into diffuse astrocytomas, oligodendrogliomas, and isocitrate dehydrogenase 1 and 2 (IDH1/2) mutant (mut) and wild-type (wt) glioblastomas, according to their histological grades, IDH1/2 status, and chromosome arm 1p and 19q (1p19q) co-deletion [1,2]. The gene discussed is IDH1; the disease is oligodendroglioma.