GLUL and plasma cell myeloma: A further, less well-described auxotrophy is for glutamine, through loss or downregulation of glutamine synthetase (GS), which has been described in multiple myeloma, ovarian cancer and oligodendroglioma cells.9–11 GS synthesises glutamine from glutamate and NH4+, which has previously been shown to be important for continued tumour proliferation, particularly when glutamine may be limiting.12 The plasma membrane glutamine transporters may therefore represent potential therapeutic targets for tumours with GS deficiency.