Immunohistochemically retained nuclear ATRX expression as a surrogate of ATRX-wildtype status is a very strong correlate for 1p19q codeletion status in IDH-mutant gliomas.2IDH-mutant astrocytomas CNS WHO 2/3/4 are molecularly defined by retained 1p19q chromosomes and the presence of ATRX-mutation, or its immunohistochemical surrogate of nuclear ATRX-staining loss. The gene discussed is IDH1; the disease is glioma.