IDH1 and glioblastoma: Interestingly, therefore, at 11q23.2 which is strongly associated with IDH mutated gliomas, the most convincing molecular mechanism is via NNMT, which encodes nicotinamide N-methyltransferase and is highly expressed in GBM relative to normal brain, causing methionine depletion-mediated DNA hypomethylation and accelerated tumour growth [23, 55].