Background: Cytochrome-c oxidase (COX) deficiency is one of the most common of the respiratory chain disorders. The mutation of the COX10 gene is very rare. Only five cases have been reported.

Case study: A 3-year-old boy was born to first degree consanguineous parents. He has a family history of a similar case in his brother and a personal history of prematurity. At the age of 10 months, he presented with psychomotor delay. Examination showed axial hypotonia, quadripyramidal syndrome and hyporeactivity to sound. Brain MRI, standard biology, and cerebrospinal fluid study were normal. The brainstem evoked response showed a bilateral deafness. A second brain MRI was done at the age of 2 years showed bifocal lesions of the corpus callosum. At the age of 3 years, he presented with irritability, ataxia, deficit of the left upper limb and swallowing disorders. Examination showed a cerebellar syndrome and left hemiparesis. A third MRI showed a vacuolar leucodystrophy. Lactatorrachia was elevated to 3.5 mmol/l (NV: 1.2-2.8). The redox cycle was in favor of mitochondrial cytopathy. A study of the respiratory chain on fibroblasts revealed a complex IV deficiency. A genetic study concluded to homozygous mutation of COX10 gene.

Conclusion: Mutation of COX10 gene is suspected in patients presented with hypotonia, ataxia, deafness, cardiomyopathy, proximal tubulopathy, lactic acidosis and Leigh syndrome. Vacuolar leukodystrophy, which was described in APOPT1 gene mutation, has never been reported in COX10 gene mutation. Early diagnosis is necessary to establish genetic counseling.