This was a surprising finding in that one would anticipate that the more proximal enzymes, such as citrate synthase, would be far more critical for GBM growth than the OGDH enzyme, especially in light of the fact that glutamine metabolism was found not to be as critical as glucose and acetate for GBM growth based on prior 13C tracing studies in brain tumor patients (31). Here, CS is linked to glioblastoma.