IDH1 and IDH2 are metabolic enzymes that are homologous. IDH stands for Isocitrate Dehydrogenase. IDH1 mutations are present in about 70% of low grade (Grade II) and intermediate grade (Grade III) gliomas including astrocytic, oligodendroglial, and mixed oligo-astrocytic tumors. IDH1 mutations are also common in secondary glioblastomas that arise from lower grade lesions. IDH1 predicts a better prognosis for a glioblastoma patient and is associated with GBMs in younger patients. IDH2 is much less common than IDH1 but is believed to have the same prognostic significance.
MGMT (O6-Methylguanine DNA Methyltransferase) is a DNA repair enzyme that removes alkyl groups from DNA. Hence, it counteracts the effects of alkylating agents like TEMAZOLAMIDE. If a tumor has a methylated promoter region of the MGMT gene, its ability to produce MGMT is impaired. It will also be susceptible to alkylating agent therapy.
By far, the most common structural deformity found is co-deletion of chromosomal arms 1p and 19q. The high frequency of co-deletion is a striking feature of this glial tumour and is considered as a "genetic signature" of oligodendroglioma. Allelic losses on 1p and 19q, either separately or combined, are more common in classic oligodendrogliomas than in either astrocytomas or oligoastrocytomas.