ATRX mutations in adult glioma arise almost exclusively in the setting of concurrent mutations in TP53 and either IDH1 or IDH2. The glioma subtype defined by this combined genotype, termed “IDHmut-noncodel”2, features almost uniformly low-level ATRX expression and exhibits a characteristic pattern of CNAs, distinct form that commonly seen in other adult glioma subtypes (Supplementary Fig. 5)2. The gene discussed is IDH2; the disease is glioma.