As well as known associations such as hemispheric H3.3G34R/V and TP53/ATRX (18/20, 90%; p = 0.0001), midline H3.3K27M and FGFR1 (8/39, 20.5%; p = 0.212, not significant), pontine H3.1K27M and ACVR1 (28/33, 84.8%; p < 0.0001), and PXA-like GBM with BRAF V600E (17/28, 60.7%; p < 0.0001), we also identified previously unrecognized co-segregating mutations including H3.3G34R/V and ARID1B (2/20, 10%; p = 0.0720), H3.3K27M DIPG and ATM and ASXL1 (5/93, 10.7%; p = 0.0473), and H3.1K27M and BCOR (6/37, 16.2%; p = 0.0022, all Fisher’s exact test) (Figure S6D). This evidence concerns the gene ARID1B and glioblastoma.