TP53 and alpha thalassemia X-linked intellectual disability (ATRX): Class-defining loss of function mutations in TP53 and ATRX genes are seen in approximately 90 and 70% of astrocytomas, respectively, (Cancer Genome Atlas Research Network, 2015; Jiao et al., 2012). The gene discussed is ATRX; the disease is astrocytoma (excluding glioblastoma).