Fig. 1: Gene expression differences in human normal brain and human glioma.

a Principal component analysis (PCA) plot of all brain samples from Genotype-Tissue Expression (GTEx) project. Samples from 13 regions fall into two groups clearly separating the cerebellum samples from the rest of the brain regions. b Principal Component analysis (PCA) plot of pooled brain samples from GTEx (with cerebellum and spinal cord removed) and The Cancer Genome Atlas (TCGA) samples using gene expression from 20,214 genes from hg19. Two clear clusters were formed, TCGA-GBM and TCGA-LGG samples fall into one cluster while the supratentorial regions from GTEx maintain the one pooled normal brain cluster from a. c PCA plot of pooled normal brain regions broken down shows minimal regional specificity and clustering based on 20,214 genes from hg19. d PCA plot showing tumor samples from TCGA using gene expression of  20,214 genes in hg19 colored by CpG Island Methylation Phenotype (CIMP) status. CIMP and non-CIMP status for TCGA samples were obtained from Bolouri et al.²⁶, and show distinct CIMP vs non-CIMP clusters based on total gene expression. Normal brain regions are displayed as circles, brain tumors are displayed as triangles.