IDH (isocitrate dehydrogenase) mutation

What it is

An IDH mutation is a change in the IDH gene (which makes the enzyme isocitrate dehydrogenase, in the forms IDH1 or IDH2). In gliomas, the presence or absence of an IDH mutation is one of the most important features for classification, and IDH-mutant gliomas generally have a better outlook than those without the mutation.

Understanding IDH (isocitrate dehydrogenase) mutation

The IDH mutation is the central dividing line in the modern classification of adult diffuse gliomas. Tumors with the mutation are classified as astrocytomas or oligodendrogliomas (depending on other features) and tend to occur in younger adults, grow more slowly, and respond better to treatment. Tumors without it (IDH-wildtype) include glioblastoma, the most aggressive type. The mutation causes the IDH enzyme to produce an abnormal substance (2-hydroxyglutarate) that drives tumor development by altering how genes are switched on and off. Because the IDH mutation so strongly affects diagnosis, prognosis, and now treatment (with IDH inhibitor drugs available for some tumors), testing for it is a standard, essential part of glioma diagnosis. Understanding the IDH mutation clarifies the single most important molecular feature in adult glioma classification.

Why it matters

Understanding the IDH mutation helps patients and families see why this is the most important molecular test in adult glioma diagnosis — it defines the tumor type, predicts a generally better outlook, and can be targeted by newer drugs.