The CRISPR Cas9 technology was used elegantly to determine how a genomic locus (rs55705857) that has been associated with increased risk to develop IDH mutant astrocytomas in humans (typically carrying IDH R132H mutations, p53 mutations, and loss of function mutation of ATRX), can be modelled in an appropriate mouse model setting. Here, IDH2 is linked to astrocytoma (excluding glioblastoma).