IDH1 and glioma: Mutations in isocitrate dehydrogenase 1 (IDH1), and less frequently in IDH2, occur in 80% of grade II and grade III astrocytomas and oligodendrogliomas, and are also found in high-grade glioblastomas that have arisen over time from these lower-grade gliomas (Staedtke et al., 2016).