A rare genetic mitochondrial oxidative phosphorylation disorder with characteristics of infantile-onset encephalomyopathy presenting with developmental delay, slowly progressive hemiplegia, intractable epileptic seizures and asymmetrical brain atrophy with dilatation of the ipsilateral ventricle system. Additional features include optic atrophy, mildly increased plasma and/or CSF lactate and decreased cytochrome c oxidase activity in skeletal muscle biopsy. [from SNOMEDCT_US]