IDH1 and glioblastoma: Approximately 55–80% of secondary glioblastomas, those that progress from low-grade diffuse astrocytoma or anaplastic astrocytoma and occur in younger patients, have somatic mutations in the isocitrate dehydrogenase 1 (IDH1) gene, which are absent in primary glioblastoma in older patients [9,14,15,16,17].