For oligodendroglioma, approximately 90% of the IDH1 mutations are canonical (R132H), and there is a higher frequency of IDH2 mutations compared to IDH-mutant astrocytomas (Hartmann et al., 2009; Cancer Genome Atlas Research Network, 2015; Eckel-Passow et al., 2015). The gene discussed is IDH1; the disease is astrocytoma (excluding glioblastoma).