Objective: To investigate the clinical characteristics and gene mutation characteristics of reversible cytochrome C oxidase (COX) deficiency myopathy. Methods: The clinical data and gene testing results of infantile reversible COX deficiency myopathy in one case were retrospectively analyzed. Results: The child was an infant with onset of disease

backward growth and development

admitted into the hospital with respiratory failure and required ventilatory assistance under tracheal intubation. The neurological examination did not show any abnormality

and the arterial blood gas analysis showed pH 7.212

blood lactate 6.3 mmol/L

partial pressure of carbon dioxide 73.8 mm Hg

creatine kinase 1

193 U/L

creatine kinase isoenzyme 155 U/L and lactate dehydrogenase 560 U/L. Magnetic resonance imaging (MRI) of the head showed retardation with the process of myelination in alba. After admission

the anti-infective and adjuvant therapy was ineffective

with persistent hyperlactatemia and abnormally elevated myocardial enzyme level. The clinical symptoms of the child were significantly improved after treatment with coenzyme Q10 and levocanidine. Genetic testing showed m.14674 T>C mutation in the mitochondrial genome

derived from the mother. Conclusion: Persistent respiratory failure and high blood lactate in infants and children require vigilance for mitochondrial myopathy

and genetic testing can help to diagnose it in a timely manner. The clinical manifestations of reversible COX deficiency myopathy are nonspecific

and early diagnosis and treatment can lead to good prognosis.