We next sought to identify the cause of discordance in MTA levels between cells in culture and human GBM tumors. Previous work by Sanderson et al.11, showed that MTAP-deleted cells accumulate less amount of MTA when cultured in restricted methionine (3 μM) or cysteine (6 μM) RPMI than when cultured in the standard formulation with 100 μM methionine and 200 μM cysteine (data replotted in Supplementary Fig. 9). The gene discussed is MTAP; the disease is glioblastoma.