LGG consist of IDH-mutant WHO grade II and III gliomas, which can be further subcategorized into IDH-mutant, 1p/19 codeleted gliomas or oligodendrogliomas, and IDH-mutant, 1p/19q retained, p53-mutant, ATRX-mutant gliomas, or astrocytomas. The gene discussed is IDH2; the disease is oligodendroglioma.