PIK3R1 and glioblastoma: Here, we found that several of the most frequently mutated genes in glioblastoma including: EGFR, PTEN, NF1, PIK3R1, RB1, PDGFRA and QKI possessed high 5 hmC levels across intronic regions and further loss of 5 hmC in tumours may reflect a loss of genome integrity13.