Foundations · Year 1 · from Foundations
Case 3: IDH-Mutant Glioma (Oncometabolite Production)
Clinical Image
Source: Radiopaedia - IDH mutant glioma - CC BY-NC-SA 3.0
Case Presentation
A 38-year-old woman presents with new-onset seizures and a 6-month history of progressive headaches. MRI brain reveals a non-enhancing infiltrative mass in the left frontal lobe with T2/FLAIR hyperintensity. Stereotactic biopsy is performed, and histopathology shows a diffuse astrocytoma. Immunohistochemistry for IDH1 R132H mutation is positive. Her neuro-oncologist explains that this mutation, found in approximately 80% of grade 2-3 gliomas, actually confers a better prognosis than IDH-wildtype tumors. The mutant IDH1 enzyme gains a new function: instead of converting isocitrate to alpha-ketoglutarate, it converts alpha-ketoglutarate to 2-hydroxyglutarate (2-HG), an oncometabolite. 2-HG competitively inhibits alpha-ketoglutarate-dependent enzymes including TET2 (involved in DNA demethylation) and histone demethylases, causing epigenetic dysregulation that promotes tumorigenesis. She undergoes maximal safe resection followed by radiation and temozolomide chemotherapy. Targeted IDH inhibitors (vorasidenib) have recently been FDA-approved for such tumors.
Key Learning Points
- IDH1 and IDH2 mutations are common in gliomas and acute myeloid leukemia; these mutations confer neomorphic enzyme activity that produces the oncometabolite 2-hydroxyglutarate (2-HG)
- 2-HG structurally resembles alpha-ketoglutarate and competitively inhibits alpha-KG-dependent enzymes, including those involved in histone and DNA demethylation, leading to epigenetic dysregulation
- Understanding this biochemical mechanism has led to targeted therapies: IDH inhibitors (ivosidenib for IDH1, enasidenib for IDH2) are approved for AML and gliomas