Histones are nuclear proteins involved in control of both DNA replication/repair and transcription, which are regulated by methylation and acetylation at specific residues. Recurrent point mutations have been described in histone H3 in pediatric gliomas. Using Droplet Digital (ddPCR) Assay we investigated the presence of the K27M mutation (in the genes for either H3.3 or H3.1) and G34V/R in all 39 patients under the age of 40 (over 18) operated at St. Michael’s hospital for astrocytoma from 2004 to 2015 in whom enough material was available. 6 patients (average age 21±5.2) harboured H3K27M mutations; tumor histology ranged from pilocytic to glioblastoma, all were located in the midline, and none was associated with mutations in IDH1 or BRAF. 10 patients (average age 30±6.8) harboured H3G34R mutations; tumor histology ranged from diffuse astrocytoma to glioblastoma, all were located in the hemispheres, and were frequently associated with mutations in IDH1 (R132H, 60%) and sometimes BRAF (V600E, 10%). We also found 17 patients harboured the IDH1 R123H mutation, which co-occurred with H3G34R in 6, and 4 patients harboured the BRAF V600E, in one case along with H3G34R. Only 26% of patients did not carry at least one of the mutations investigated; Histone mutations are present in 35% of midline tumours and 40% of hemispheric astrocytomas in this age group.
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