This review will focus on the pediatric types of DHGGs (except the diffuse midline glioma, H3 K27-altered) and the two grade 4 adult types of diffuse gliomas, namely the astrocytoma, IDH-mutant grade 4 (formerly known as glioblastoma, IDH-mutant), and the glioblastoma, IDH-wildtype (1). The gene discussed is IDH2; the disease is diffuse midline glioma.