A significant decrease in average copy number for genes tested on 19q (CCNE1 and PPP2R1A) was noted in oligodendroglioma (average CN = 1.23 ± 0.18) compared to IDH-mutant infiltrating astrocytoma (average CN = 1.96 ± 0.29; p = 1.29 × 10–11; Fig. 2a) and IDH-wild type infiltrating astrocytoma (average CN = 2.24 ± 0.38; p = 3.51 × 10–16; Fig. 2a). Here, IDH1 is linked to oligodendroglioma.