In this study, mean GDF15 levels were ranked in the following order: Leigh syndrome (LS); mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS); Kearns–Sayre syndrome (KSS); overlapping MELAS/LS; and mitochondrial encephalopathy and lactic acidosis (MELA). The gene discussed is GDF15; the disease is Leigh syndrome.