Homozygous deletions were essentially restricted to high-grade gliomas including 29% (5/17) of IDH-mutant 1p/19q codeleted OG (grade 3), 46% (29/63) of IDH-wt GBM, and 33% (3/9) of midline H3K27-altered gliomas. Here, IDH1 is linked to central nervous system cancer.