Since ATRX mutations result in protein loss and TP53 mutations in p53 nuclear accumulation [12], a diffuse low-grade IDH-mutated glioma with astrocytic morphology, ATRX loss, and p53 diffuse and strong staining can be diagnosed as IDH-mutant diffuse astrocytoma in the absence of 1p/19q testing (Figure 1) [13]. The gene discussed is IDH2; the disease is glioma.