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We report on the progression of myopathology by comparing two biopsies from a patient with a Kearns-Sayre-Syndrome. The first biopsy was taken in 1979 and showed 10% ragged-red fibers. Myopathic changes were slight including internal nuclei and fiber splitting in 10% of the fibers. Electron microscopy revealed typical mitochondrial abnormalities with regard to number and shape. In 1989 a second biopsy was performed for an extended analysis of mitochondrial DNA. This time less than 5% of all fibers were ragged-red. Severe myopathic changes could be detected which so far has rarely been reported in mitochondrial cytopathy.

Kearns-Sayre syndrome has been associated with large heteroplasmic mitochondrial DNA deletions and morphological alterations at the cytological level. We have measured the activities of different respiratory chain complexes in 3 patients presenting mitochondrial DNA deletions and found no close correlation between gene deletions and enzymatic activities. These data, therefore, point out the importance of analyses at the mitochondrial DNA level in such mitochondrial disorders because gross biochemistry may miss any defect.