To emphasize the biological differences of brain tumors typically occurring in different age groups, CNS5 features a grouping of IDH-mutant gliomas together with glioblastomas, IDH-wildtype as “adult-type” diffuse gliomas, separated from “pediatric type” low- and high-grade diffuse gliomas, even though IDH-mutant gliomas can occasionally develop in the pediatric population as well. This evidence concerns the gene IDH1 and glioma.