IDH2 and astrocytoma (excluding glioblastoma): In patients with Ollier's disease, isocitrate dehydrogenase 1 (IDH1) and isocitrate dehydrogenase 2 (IDH2) mutations were shown to be a predisposing factor to the development of astrocytomas in conjunction with subsequent mutations in adenosine triphosphate (ATP)-dependent helicase ATRX (ATRX) and tumor protein p53 (TP53).