ATRX and astrocytoma (excluding glioblastoma): As stated above, the recent molecular studies have allowed for identification of two major classes of IDH-associated gliomas: the IDH-astrocytoma (IDH-A) characterized by TP53 and ATRX mutation and the IDH-oligodendroglioma (IDH-O), characterized by loss of chromosome arms 1p and 19q and mutations in TERT promoter.