The vast majority of astrocytomas are classified as the IDH mutant with 1p/19q-intact (IDHMUT/1p/19q+) type, while oligodendrogliomas are classified as the IDH mutant with 1p/19q co-deletion (IDHMUT/1p/19q−) type. The gene discussed is IDH1; the disease is astrocytoma (excluding glioblastoma).