For the TCGA data set, the correlation was decreased somewhat (Pearson r = 0.25 compared to 0.36 for the full data set) but still highly significant ( P = 6 × 10 -5 ), demonstrating that the correlation with age is only partially explained by IDH1 status.
Nevertheless, analysis of microarray expression data from TCGA [ 11 , 46 ] for 397 glioblastoma cases (Additional file 4 ) revealed a clear trend for core upregulated GNS genes to be more highly expressed in glioblastoma tumors than in non-neoplastic brain tissue ( P = 0.02, randomization test; Figure 3a ) and an opposite trend for core downregulated genes ( P = 3 × 10 -5 ; Figure 3c ).