IDH1 and oligodendroglioma: The current version of the DNA methylation-based CNS tumor classification system distinguishes three subclasses within the methylation class family glioma, IDH-mutant: subclass astrocytoma (mostly accounts for WHO grade II and III), subclass high-grade astrocytoma (mostly accounts for WHO grade III and IV) and subclass 1p/19q-codeleted oligodendroglioma (including both WHO grade II and III) [14].