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Mitochondrial myopathy with progressive decrease in mitochondrial tRNA(Leu)(UUR) mutant genomes
Y Kawakami1, R Sakuta, K Hashimoto
1Department of Pediatrics, Nippon Medical School, Tama Nagayama Hospital, Tokyo, Japan.
Abstract:
A female patient with mitochondrial myopathy had a mitochondrial DNA mutation at nucleotide pair 3243, commonly seen in patients with mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes (MELAS), but unlike MELAS patients, she had no central nervous system symptoms. Muscle weakness, which was most severe when she was 7 years old, improved gradually with age. Comparison of two muscle biopsies obtained at an interval of 12.5 years (7 and 20 years of age, respectively), revealed that the number of ragged-red fibers was markedly decreased and histochemical cytochrome c oxidase activity increased in parallel with the decrease in population of mutant genomes.
Insights
A patient with mitochondrial myopathy and a common MELAS mutation showed muscle weakness that improved with age. Muscle biopsies revealed reduced ragged-red fibers and increased enzyme activity, correlating with fewer mutant mitochondrial DNA genomes.
Area of Science:
- Genetics
- Neurology
- Mitochondrial Diseases
Background:
- Mitochondrial myopathy is a condition affecting muscle energy production.
- The A3243G mutation in mitochondrial DNA is frequently associated with MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and strokelike episodes).
Observation:
- A female patient presented with mitochondrial myopathy and the A3244G mitochondrial DNA mutation, but lacked central nervous system involvement typical of MELAS.
- Muscle weakness was most pronounced at age 7 and gradually improved over time.
Findings:
- Muscle biopsies at ages 7 and 20 showed a significant decrease in ragged-red fibers.
- Histochemical analysis revealed increased cytochrome c oxidase activity in parallel with the reduction of mutant mitochondrial DNA genomes.
Implications:
- This case highlights the phenotypic variability of the A3243G mitochondrial DNA mutation.
- The findings suggest a potential for natural improvement in certain mitochondrial myopathies with age.
- Reduced mutant genome load may correlate with improved muscle function and biochemical markers.