A very rare inherited metabolic disorder characterized by deficiency of the enzyme cytochrome-C oxidase. It may be manifested as an isolated myopathy or a systemic disorder. Signs and symptoms include myotonia, dysfunction of the heart, kidney, and brain, and lactic acidosis. The disease is Monarch Disease Ontology term MONDO_0033885 (mitochondrial complex IV deficiency, nuclear-type). Also known as: Cytochrome C Oxidase Deficiency, cytochrome-C oxidase deficiency, cytochrome-c oxidase deficiency disease, isolated COX deficiency, isolated mitochondrial respiratory chain complex IV deficiency, mitochondrial complex IV deficiency, mitochondrial respiratory complex IV deficiency.