FH and hereditary leiomyomatosis and renal cell cancer: Moreover, fumarate accumulation is involved in a process called succination, in which there is nucleophilic addition of fumarate on cysteine residues (Michael addition type reaction) forming adducts of S-2-succynil cysteine (2SC), that have been proposed as marker for HLRCC and PRCC type II featuring FH mutations that are not detected as changes in the protein levels [152].