IDH2 and cancer: Fumarate and succinate antagonize the roles of α-KG In addition to IDH1 and IDH2, germinal and somatic mutations of fumarate hydratase (FH) and succinate dehydrogenases (SDHA, SDHB, SDHC, SDHD, and SDHAF2), encoding FH and SDH enzymes, are common in a number of human cancers (Baysal et al., 2000; Astuti et al., 2001; Hao et al., 2009; Kaelin, 2009; Bayley et al., 2010; Oermann et al., 2012).