FGF21 and mitochondrial disease: In mouse models of mitochondrial diseases as well as in human patients, skeletal muscle is known to secrete high amount of Fgf21.28 In adult Drp/MC mice, serum Fgf21 concentration was 14-fold higher compared with control mice (WT 148±25 vs Drp/MC 2084±269 pg/ml) (Figure 5f).