To compare the utility of CDKN2A HD and the histology-based WHO grading criteria, Appay et al. analysed 428 IDH-mutant astrocytomas (1p/19q non-co-deletion) and 483 anaplastic oligodendrogliomas (1p/19q co-deleted) using a combination of SNP arrays, CGH arrays, and targeted gene panel NGS data. The gene discussed is IDH2; the disease is astrocytoma (excluding glioblastoma).