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The Human Phenotype Ontology (HPO) is downloaded weekly from The file downloaded is considered the "last stable build" available for the ontology. For more about the HPO, view their website at

Term:Ragged-red muscle fibers
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Accession:HP:0003200 term browser browse the term
Definition:An abnormal appearance of muscle fibers observed on muscle biopsy. Ragged red fibers can be visualized with Gomori trichrome staining as irregular and intensely red subsarcolemmal zones, whereas the normal myofibrils are green. The margins of affect fibers appear red and ragged. The ragged-red is due to the accumulation of abnormal mitochondria below the plasma membrane of the muscle fiber, leading to the appearance of a red rim and speckled sarcoplasm.
Comment:This finding is demonstrated by muscle biopsy. Note that additionally, muscle fibers with mitochondrial proliferation stain darkly for succinic dehydrogenase (SDH).
Synonyms:exact_synonym: Mitochondrial proliferation in muscle tissue;   Ragged-red fibers;   Ragged-red fibres;   Ragged-red muscle fibres
 alt_id: HP:0009076
 xref: UMLS:C3275417

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  Human phenotype 0
    Phenotypic abnormality 0
      Abnormality of the musculoskeletal system 0
        Abnormality of the musculature 0
          Abnormal skeletal muscle morphology 0
            Abnormal muscle fiber morphology 0
              Ragged-red muscle fibers 0
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