Recently, an accumulation of fumarate in FH‐deficient renal cell carcinoma (RCC) has been shown to lead to an increase in mtDNA mutations and impaired respiratory complex activity due to the fumarate‐mediated succination of POLG, TWINKLE and TFAM proteins, thus promoting an irreversible shift to aerobic glycolysis and disease progression [165]. The gene discussed is POLG; the disease is renal cell carcinoma.