Whereas in the WHO CNS 4, glioblastomas (GBMs) included both IDH- mutant and IDH-wild type tumors, adult-type diffuse gliomas are divided into distinct categories on the basis of IDH-mutation status in CNS 5, with the term glioblastoma, applying only to IDH wild-type tumors. The gene discussed is IDH1; the disease is glioblastoma.