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Muscle histopathology in myoclonus epilepsy with ragged-red fibers (MERRF)
1Division of Ultrastructural Research, National Institute of Neuroscience, National Center of Neurology and Psychiatry (NCNP), Tokyo, Japan.
Abstract:
Histopathologic findings were examined in skeletal muscle biopsies from 6 patients with myoclonus epilepsy with ragged-red fibers (MERRF) who had an A to G base substitution at mitochondrial DNA (mtDNA) nucleotide pair 8344. In addition to variation in fiber size and ragged-red fibers, all specimens in cross sections showed focal cytochrome c oxidase (CCO) deficiency, suggesting that this finding is crucial in elucidating the role of the mutant mtDNA in the pathogenesis of this disorder. Along the length of single muscle fibers, defects in CCO activity were distributed segmentally with blurred borders in 5 patients which were in contrast with segmental defects with sharply delineated borders seen in chronic progressive external ophthalmoplegia with deleted mtDNA. These morphologically heterogeneous defects in CCO activity may in part be due to differing populations of and distributions of wild and mutants mtDNAs.
Insights
Myoclonus epilepsy with ragged-red fibers (MERRF) patients with a specific mitochondrial DNA mutation show focal cytochrome c oxidase deficiency in skeletal muscle. This deficiency is crucial for understanding MERRF pathogenesis.
Area of Science:
- Mitochondrial genetics
- Neuromuscular disorders
- Cellular pathology
Background:
- Myoclonus epilepsy with ragged-red fibers (MERRF) is a maternally inherited mitochondrial disorder.
- Ragged-red fibers and variable fiber size are characteristic histopathologic features of MERRF.
- Specific mutations in mitochondrial DNA (mtDNA) are implicated in MERRF pathogenesis.
Purpose of the Study:
- To investigate histopathologic findings in skeletal muscle of MERRF patients with a specific mtDNA mutation.
- To correlate cytochrome c oxidase (CCO) activity defects with the presence of mutant mtDNA.
- To elucidate the role of mutant mtDNA in MERRF pathogenesis.
Main Methods:
- Histopathologic examination of skeletal muscle biopsies.
- Analysis of mitochondrial DNA (mtDNA) for specific base substitutions (A to G at nucleotide pair 8344).
- Assessment of cytochrome c oxidase (CCO) activity in muscle fibers.
Main Results:
- All 6 MERRF patients with the A8344G mtDNA mutation exhibited focal CCO deficiency in skeletal muscle.
- CCO defects were segmentally distributed with blurred borders in 5 patients.
- These findings contrast with sharply delineated CCO defects seen in other mitochondrial disorders.
Conclusions:
- Focal CCO deficiency is a key histopathologic finding in MERRF associated with the A8344G mtDNA mutation.
- Morphologically heterogeneous CCO defects may result from varying distributions of wild-type and mutant mtDNA.
- Understanding these defects is crucial for MERRF pathogenesis research.