Use of DNA copy number analysis of grade 2-4 gliomas to reveal differences in molecular ontogeny associated with IDH mutation status.

Abstract

2026 Background: The genetic alterations of glioma have been studied extensively. IDH1 mutation is associated with younger age and better survival. However, differences in molecular ontogeny within glioma related to IDH1 mutation remain unknown. Here we describe a detailed analysis of copy number alterations (CNA) between IDH1mut vs IDH1wt gliomas of grade 2-3 and 4. Methods: CNA were detected by molecular inversion probes (Affymetrix) and analyzed with Nexus Copy Number Software (BioDiscovery). DNA was extracted from 94 patient FFPE samples including grade 2-3: IDH1wt (n = 17) and IDH1mut (n = 28), and grade IV: IDH1wt ( n = 25) and IDH1mut(n = 24). Chromothripsis was detected using a stringent criteria of at least ten switches of CNA in individual chromosomes. Results: We validated prior findings that IDH1wt GBM have higher frequency of Chr7 amplification (including EGFR) and loss of Chr10 (including PTEN). Other CNA across all grades were: gain of 19q12 and loss of 14q11 in IDH1wt, and gain of 11q21, 10p11, 8q21 and loss of 11p15, 19q13 in IDH1mut. Within grade 2-3 samples, few CNA were associated with mutation status: 2-3wt demonstrated higher frequencies of gain of 7q and loss of 10q, 14q11, and 22q13, while 2-3mut demonstrated higher frequencies of 11q21 gain and 19q13 loss. Grade 4 tumors demonstrated more CNA that differed by mutation status, with 4wt tumors demonstrating gain of 7 and loss of 10 and 14q11, while 4mut demonstrated gains of 8q, 10p, 12p13, 1q23, and loss of 11p15, 3p, 19q13, among others. Comparison of grade 2-3mut vs grade 4mut tumors demonstrated larger number of CNA in the grade 4mut tumors including gain of 1p, 14q, 13q33, 9p, 8q and loss of 22q, 11p15, 10q, and 3p, among others. A significantly higher incidence of chromothripsis events was observed in grade 4mut compared to grade 4wt (p = 0.0374). Conclusions: CNA analysis showed significant differences in molecular ontogeny between IDH1wt and IDH1mut, some of which may further elucidate pathogenesis. Significant CNA increases and increased chromthripsis in grade 4mut support malignant transformation of low grade gliomas through accumulation of genomic instability and genomic catastrophe.