Background: Cytochrome-c oxidase (COX) is the terminal enzyme of the mitochondrial electron transport chain, and COX deficiency is a common cause of mitochondrial diseases. Cytochrome-c oxidase is composed of 13 subunits, of which 3 are encoded by mitochondrial DNA and 10 by nuclear DNA. Mutations have been identified in each of the 3 mitochondrial DNA genes but in none of the nuclear DNA genes. However, COX deficiency has been attributed to mutations in several nuclear DNA-encoded ancillary proteins needed for COX assembly and function. Despite this progress, the molecular basis of COX deficiency remains elusive in many patients, justifying the identification and screening of additional COX assembly genes, such as COX16, COX19, and PET191. Objective: To determine if COX16, COX19, and PET191 are implicated in human COX deficiency. Methods: Mutation screening was performed on 53 patients with isolated COX deficiency by direct sequencing of COX19 and by single-strand conformational polymorphism analysis for COX16 and PET191. Results: No mutations were found in COX16, COX19, or PET191 in these patients. Conclusions: The COX16, COX19, and PET191 genes are either not involved or very rarely involved in human COX deficiency. Mutations in additional COX assembly genes remain to be identified.
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