As an alternative, FGF21 and GDF15 have emerged as promising biomarkers for disease severity and potentially for treatment response in selected mitochondrial myopathy genotypes.30 This is particularly relevant given the current paucity of effective treatments for mitochondrial myopathies, which has resulted in limited data on the utility of these biomarkers in clinical settings. Here, FGF21 is linked to Mitochondrial myopathy.