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  • Title: Mitochondrial myopathy with autophagic vacuoles in patients with the m.8344A>G mutation.
    Author: Yuan JH, Sakiyama Y, Higuchi I, Inamori Y, Higuchi Y, Hashiguchi A, Higashi K, Yoshimura A, Takashima H.
    Journal: J Clin Pathol; 2013 Aug; 66(8):659-64. PubMed ID: 23559353.
    Abstract:
    BACKGROUND AND AIMS: In mitochondrial myopathy, autophagy is presumed to play an important role in mitochondrial dysfunction. Rimmed vacuoles (RVs), a sign of autophagy, can be seen as a secondary phenomenon in muscle ragged-red fibres (RRFs), whereas the uncommon presentation is that some fibres contain RVs, but without any mitochondrial abnormalities. To investigate the pathogenesis beneath this pathological phenomenon. METHODS: We reviewed 783 skeletal muscle specimens and selected five obtained from patients with suspected mitochondrial myopathy, characterised by clearly visible autophagic vacuoles in non-RRFs, besides the coexistence of RRFs and cytochrome oxidase-negative fibres. Immunohistochemical staining with LC-3, and electron microscopy studies were performed. Using resequencing microarray and a next-generation sequencing system, the mitochondrial DNA was screened for mutations and the heteroplasmic level was measured in skeletal muscle and blood. RESULTS: Muscle fibres with RVs and RRFs, as well as some morphologically normal fibres, stained strongly for LC-3. Electron microscopy disclosed significant abnormal mitochondrial proliferation and existence of autophagic vacuoles. After mutation screening, m.8344A>G in the tRNA(Lys) gene was detected in two patients. The heteroplasmy of mutated G was 45.1% in skeletal muscle and 17.8% in blood in patient 1; patient 2 exhibited 80.3% mutated G in skeletal muscle and 25.2% in blood. CONCLUSIONS: These findings demonstrate a new pathological phenotype for the m.8344A>G mutation- related disease and also provide pathological evidence of a correlation between mitochondrial abnormalities and autophagy.
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