IDH1 and glioma: We termed tumors with this genetic signature “I-A gliomas”, denoting that these tumors had alterations in either IDH1 or IDH2 and in ATRX. Most I-A adult gliomas also had mutations in TP53 (94%, n=87), and the majority of adult gliomas with TP53 mutations had the I-A signature (72%, n=113).