Further studies have shown that IDH mutation is an early event in gliomagenesis (‘driver mutation’), and likely precedes the development of the 1p/19q codeletion, the latter possibly specifically driving a diffuse glioma towards the classic oligodendroglioma morphologic phenotype, whereas superimposed TP53 and ATRX mutations drive it towards the astrocytoma phenotype instead [3, 124, 125]. The gene discussed is IDH1; the disease is oligodendroglioma.