They can be subclassified as either astrocytoma or oligodendroglioma by the presence of the tumor protein p53 (TP53) pathogenic alterations and alpha-thalassemia/intellectual disability X-linked syndrome (ATRX) loss in the first case, or by the revealing complete deletion of both of the short arm of chromosome 1 (1p) and the long arm of chromosome 19 (19q) (1p/19q-co-deletion) or telomerase reverse transcriptase (TERT) promoter (p-TERT) pathogenic DNA sequence alterations in the second (Figure 1). The gene discussed is ATRX; the disease is astrocytoma (excluding glioblastoma).