GDF15 is a circulating cytokine and an established biomarker of mitochondrial disorders, sensitive to disease progression and treatment response in these conditions,46,47,68 as well as in cardiovascular,69,70 kidney71 and liver disease,72,73 and diabetes mellitus.74 We found that serum GDF15 was significantly elevated in all analysed CMT patient subgroups (Fig. 6E), and show that serum GDF15 is highly selective as a diagnostic marker of CMT with a threshold above 417.4 ng/μl giving a sensitivity of 88.9% and a specificity of 92.9% to differentiate symptomatic CMT patients from controls. The gene discussed is GDF15; the disease is Charcot-Marie-Tooth disease.