[Deletions of mitochondrial DNA in Kearns-Sayre syndrome]

Single large-scale deletions of mitochondrial DNA (mtDNA) are found in 70 to 80% of Kearns-Sayre syndrome (KSS) patients. Most deletions are flanked by direct repeats up to 13 nucleotides in length. The incidence of ragged-red fibers and cytochrome c oxidase-negative fibers in muscle is correlate with the amount of deleted mtDNA. Recently, study with 'cybrid' cell lines, which have different proportions of deleted mtDNA, showed that accumulation of deleted mtDNA to over 60% of the total mtDNA resulted in progressive inhibition of overall mitochondrial translation, as well as, reduction of cytochrome c oxidase activity. These results suggest that deletion of mtDNA alone is sufficient for the mitochondrial dysfunction in KSS.