NDUFB4 and juvenile dermatomyositis: NADH dehydrogenase (NDUFA4 and NDUFB4), ATP synthase (ATP5O and ATP5B) and cytochrome c oxidase (COX) family (COX5B, COX6A2 and COX7C) are crucial molecules involved in the oxidative phosphorylation in mitochondrial metabolism, and the decreased levels of these molecules suggested a crucial role of impaired mitochondrial phosphorylation and lower oxidative capacity in the pathogenesis of JDM, accounting for the extremity weakness in JDM patients.