GDF15 and myopathy: The mean circulating concentration of GDF-15 was almost identical in healthy children (mean = 350.3, SEM = 21 pg/mL) and in myopathic non-mitochondrial controls (349.1 pg/mL) whereas FGF-21 was higher in children with myopathy (136.1 pg/mL) than in unaffected controls (77.6 pg/mL).