TCA cycle genes, encoding isocitrate dehydrogenase (IDH1 and IDH2), fumarate hydratase (FH), and succinate dehydrogenase (SDHA, SDHB, SDHC, SDHD, and SDHAF2) are mutated both germinally and somatically in a number of human cancers. The gene discussed is IDH2; the disease is cancer.