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Published on: June 5, 2010
Mitochondrial DNA depletion in sporadic inclusion body myositis
Padmanabh S Bhatt1, Charalampos Tzoulis2, Novin Balafkan3
1Department of Neurology, Haukeland University Hospital, 5021 Bergen, Norway.
Abstract:
Sporadic inclusion body myositis (sIBM) is a late onset disorder of unkown aetiology. Mitochondrial changes such as cytochrome oxidase deficient fibres are a well recognised feature and mitochondrial DNA (mtDNA) deletions have also been reported, but not consistently. Since mtDNA deletions are not present in all cases, we investigated whether other types of mtDNA abnormality were responsible for the mitochondrial changes. We studied 9 patients with sIBM. To control for fibre loss or replacement with inflammatory cells, we compared sIBM patients with necrotising myopathy (n = 4) as well as with healthy controls. Qualitative anlysis for mtDNA deletions and quantitative measurement of mtDNA copy number showed that muscle from patients with sIBM contained on average 67% less mtDNA than healthy controls (P = 0.001). The level of mtDNA was also significantly depleted in sIBM when compared to necrotising myopathy. No significant difference in copy number was seen in patients with necrotising myopathy compared to controls. Deletions of mtDNA were present in 4 patients with sIBM, but not all. Our findings suggest that mtDNA depletion is a more consistent finding in sIBM, and one that may be implicated in the pathogenesis of the disease.
Insights
Mitochondrial DNA (mtDNA) depletion, not deletions, is a consistent finding in sporadic inclusion body myositis (sIBM). This study reveals significantly lower mtDNA levels in sIBM patients, suggesting its role in disease development.
Area of Science:
- Neurology
- Mitochondrial Biology
- Muscle Diseases
Background:
- Sporadic inclusion body myositis (sIBM) is a late-onset muscle disorder with unknown causes.
- Mitochondrial abnormalities, including cytochrome oxidase deficiency and mitochondrial DNA (mtDNA) deletions, are observed in sIBM but not consistently.
- The role of other mtDNA abnormalities in sIBM pathogenesis remains unclear.
Purpose of the Study:
- To investigate the prevalence and significance of mtDNA abnormalities, specifically depletion and deletions, in sporadic inclusion body myositis (sIBM).
- To compare mtDNA levels and deletions in sIBM patients with those in necrotising myopathy and healthy controls.
Main Methods:
- Studied 9 patients with sIBM, 4 with necrotising myopathy, and healthy controls.
- Performed qualitative analysis for mtDNA deletions.
- Quantitatively measured mtDNA copy number in muscle tissue.
Main Results:
- Muscle tissue from sIBM patients showed a significant 67% reduction in mtDNA copy number compared to healthy controls (P=0.001).
- mtDNA levels were also significantly lower in sIBM compared to necrotising myopathy.
- mtDNA deletions were present in only 4 out of 9 sIBM patients, indicating inconsistency.
Conclusions:
- Mitochondrial DNA depletion is a more consistent finding in sporadic inclusion body myositis (sIBM) than mtDNA deletions.
- The significant depletion of mtDNA in sIBM suggests it may play a crucial role in the disease's pathogenesis.
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