Isocitrate Dehydrogenase 1 (IDH1) is a soluble, cytosolic enzyme involved in the TCA metabolic cycle. The most notable mutation in this enzyme, R132H, is clinically indicated in the majority of astrocytomas and oligodendroglial tumours, with the mutation being associated with more favourable prognosis and increased survival in those patients. IDH1 R132H is also useful in the differential diagnosis between anaplastic glioma and glioblastoma.