FH and neoplasm: Heterozygous germline mutations in genes involved in lipoic acid synthesis or the OGDHC have not been characterized, but it is in these patients that loss of heterozygosity may promote tumor formation as has been shown for heterozygous mutations in the TCA cycle enzymes succinate dehydrogenase (SDH) and fumarate hydratase (FH) (Pollard et al., 2007, Selak et al., 2005).