The presence and effect of chromosomal instability in adult diffuse gliomas is not as well understood as in other neoplasms, with relatively few studies examining the effects of CIN, chromothripsis, and mutations in genes with primary functions related to the maintenance of overall genomic stability, but the impact of overall copy number burden in IDH-mutant astrocytoma has been demonstrated in a number of different studies. The gene discussed is IDH2; the disease is astrocytoma (excluding glioblastoma).