GDF15 and mitochondrial disease: Moreover, impaired mitochondrial respiratory chain activities in muscle and impaired mitochondrial respiration in fibroblasts were detected in the patient reported by Batzios et al.,9 and in P7, increased alanine in blood and CSF, elevated serum GDF-15 and FGF-21 and Krebs cycle metabolites in urine were detected, suggesting mitochondrial disease and leading to cofactors supplementation in this patient.