SDHB and neoplasm: Knockdown of FH and SDH results in elevated intracellular levels of fumarate and succinate, respectively, both of which broadly inhibit the activity of α-KG-dependent dioxygenases.55 On the other hand, ectopic expression of tumour-derived FH and SDH mutants inhibits histone demethylation and hydroxylation of 5 mC.