IDH1 and glioblastoma: The co-occurrence of G-CIMP/IDH1 mutation positivity in the proneural, neurogenesis-related subtype further suggests that IDH1 mutation and/or G-CIMP may confer neoplastic susceptibility to a common neuron/oligodendrocyte precursor cell of origin (Kriegstein and Alvarez-Buylla, 2009), a hypothesis supported by the comparative expression profiling data that showed enrichment of genes expressed in purified, cultured murine oligodendrocytes in proneural GBM (Verhaak et al, 2010).