Heterozygous deletions were observed in high-grade gliomas including 35% (6/17) of IDH-mutant 1p/19q oligodendrogliomas (grade 3), 20% (1/5) of IDH-mutant astrocytomas (grade 3), 5% (3/63) of IDH-wt GBM, and 55% (5/9) of high-grade diffuse pediatric gliomas, especially H3 and IDH-wt. The gene discussed is IDH1; the disease is central nervous system cancer.