ATRX and astrocytoma (excluding glioblastoma): Astrocytomas and oligodendrogliomas both develop by acquiring IDH mutations at an early stage, as described above, but further develop into astrocytomas by sequential mutations in TP53 and ATRX, whereas oligodendrogliomas develop by acquiring IDH mutations followed by oligodendrogliomas are caused by IDH mutation followed by deletion of 1p19q and mutation of the TERT promoter, followed by mutation of CIC.