GDF15 and mitochondrial disease: Elevated levels of GDF15 have been observed in patients with mitochondrial diseases, and its levels have been correlated with disease severity [16].A study found a significant positive correlation between circulating cell-free mitochondrial DNA (ccfmtDNA) levels and GDF-15 concentrations in cerebrospinal fluid (CSF) of 25 patients with mitochondrial diseases [17].However, no previous studies have explore the relationship between GDF15 and mtDNA copy number in peripheral blood.