IDH1 and glioma: Our research group investigated the apparent drivers of the increased production and excretion of proline by cells expressing an oncogenic mutant form of the enzyme, isocitrate dehydrogenase 1 (IDH1), which is regularly observed in grade II and III gliomas and around 10% of grade IV gliomas (glioblastomas).42,43 The normal activity of IDH1 involves the NADPH-driven carboxylation of α-ketoglutarate to isocitrate, which is reversible depending on the redox state of the cell.