IDH1 and diffuse midline glioma: Pediatric-type diffuse gliomas are now categorized into four high-grade types (diffuse midline glioma (DMG), H3 K27-altered; diffuse hemispheric glioma, H3 G34-mutant; diffuse pediatric-type high-grade glioma, H3-wildtype and IDH-wildtype; and infant-type hemispheric glioma) and four low-grade types (Tables 1 and 2; diffuse astrocytoma, MYB- or MYBL1-altered; angiocentric glioma (AG); polymorphous low-grade neuroepithelial tumor of the young (PLNTY); and diffuse low-grade glioma, MAPK pathway-altered (DLGG-MAPK)).