Deletions of mitochondrial DNA in Kearns-Sayre syndrome

We have identified large-scale deletions in muscle mitochondria! DNA (mtDNA) in seven of seven patients with Keams-Sayre syndrome (KSS). We found no detectable deletions in the mtDNA of ten non-KSS patients with other mitochondrial myopathies or encephaiomyopathies, or three normal controls. The deletions ranged in size from 2.0 to 7.0 kb, and did not localize to any single region of the mitochondria! genome. The proportion of mutated genomes in each KSS patient ranged from 45% to 75% of total mtDNA. There was no correlation between the size or site of the deletion, biochemical abnormality of mitochondrial enzymes, or clinical severity. The data bolster arguments that KSS is a unique disorder and genetic in origin.