IDH1 and glioblastoma: However, the HSR-GBM cell line possesses wild-type alleles for IDH1/2 [34, 35], which makes it an excellent model to investigate the impact of mtDNA content in tumour-initiating cells on DNA methylation patterns during tumorigenesis, especially as non-mutated IDH1 has been shown to promote cell growth in GBM [44].