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Late-Onset Mitochondrial Myopathy Ann Neurol 37:16-23, 31995., Johnston,W.,et al, 1995 See this aricle in Pubmed Article Abstract In the majority of patients with mitochondrial encephalomyopathies,signs and symptoms appear in the first three decades of life.Here we report on a group of nine older(>69 years old)with late onset skeletal myopathy characterized by focal accumulations of deleted mitochondrial DNAs(mtDNAs) and altered muscle energy status,suggestive of a primary mitochondrial disease.The clinical phenotype was somewhat variable.However,all patients shared a common feature of insidious moderate proximal muscle weakness; some also showed fatigability and axial muscle weakness.In situ hybridization analysis demonstrated accumulations of messenger RNAs transcribed from deleted mtDNAs in a relatively large number of muscle fibers in the patient group.These fiber segments appeared as ragged red with the modified Gomori trichrome stain and hyperreactive with a modified succinase dehydrogenase stain.Most were negative for cytochrome c oxidase activity.On transverse sections,their mean frequency was 0.69%(trichrome) and 1.97%(succinase dehydrogenase)significantly above control levels. Multiple mtDNA deletions were demonstrated by the polymerase chain reaction in both the patients and an age-matched control group,but not in younger control subjects.Phosphorus 13 magnetic resonance spectroscopy of resting muscle showed a decreased phosphocreatine-inorganic phosphate ratio in the patient group.The myopathy in this group of patients appears to result from mitochondrial dysfunction related to the clonal expansion of different mtDNA deletions in individual fiber segments.While the origin of the mtDNA mutations is not clear,the phenotype seems to represent an exaggerated form of what is observed in the normal aging process.

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(click to filter results - removes previous filter) fatigue mitochondrial disease muscle biopsy muscle weakness muscle weakness,proximal myopathy myopathy,mitochondrial old age,neurology of polymerase chain reaction weakness

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