In IDH-mutant GBM cells, the oncometabolite D-2-HG interferes with the homologous recombination (HR) pathway by masking H3K9 trimethylation signal through hypermethylation, preventing the recruitment of homology-dependent repair factors to the site of double strand break (DSB), including ATM and histone demethylase KDM4B [140, 141]. The gene discussed is IDH1; the disease is glioblastoma.