Since their first identification in 2008 in a subgroup of diffusely infiltrating gliomas, the isocitrate dehydrogenase mutations have played a leading role in the diagnostic and therapeutic approach to gliomas, initially with the inclusion of the IDH-mutation status into the 2016 WHO Classification of the tumors of the CNS [44], and subsequently accounting for the definition of a distinct family of tumors ranging from low-grade to high-grade in the most recent 2021 Classification [12], including astrocytoma and oligodendroglioma. The gene discussed is IDH3A; the disease is astrocytoma (excluding glioblastoma).