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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:Abnormal muscle fiber morphology
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Accession:HP:0004303 term browser browse the term
Definition:Any abnormality of the skeletal muscle cell. Muscle fibers are subdivided into two types. Type I fibers are fatigue-resistant and rich in oxidative enzymes (they stain light with the myosin ATPase reaction), and type II fibers are fast-contracting, fatigue-prone, and rich in glycolytic enzymes (these fibers stain darkly). Normal muscle tissue has a random distribution of type I and type II fibers.
Comment:Normal human muscle is composed of many individual muscle fibers bundled together by layers of connective tissue that are arranged in a nesting-doll like fashion. The inner most structure, the single muscle fiber, is covered by a thin layer of primarily reticular fibers called the endomysium. The endomysium is quite inconspicuous and muscle fibers appear to be in direct contact with each other. The finest capillaries, nerve twigs and lymphatic capillaries are found within the endomysium. Groups of muscle fibers are bound together by the thicker perimysium, forming structures called fascicles. Capillaries, nerve fibers and lymphatic vessels also track in the perimyseum. Bundles of fascicles are encased within the dense irregular connective tissue of the epimysium. These connective tissue layers provide mechanical protection for the muscle fibers and increase the tensile strength of the muscle. The layers are continuous with the tendon, which provides attachment to bone. Individual muscle fibers are syncytia, formed by embryonic fusion of many myoblasts or later, myosatellite cells. Each muscle fiber contains many nuclei, peripherally positioned immediately adjacent to the sarcolemmal membrane. In healthy muscle only 3-5 percent of fibers contain nuclei that are located internally, within the cell, but many disease processes lead to internal nuclei. Each nucleus provides a segment of the cell with needed translated protein products.
Synonyms:exact_synonym: Abnormal muscle fibre morphology;   Abnormal skeletal muscle fiber morphology;   Abnormal skeletal muscle fibre morphology;   Abnormality of muscle fibers;   Abnormality of muscle fibres
 alt_id: HP:0003706;   HP:0011806
 xref: UMLS:C4021663

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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
              Abnormal muscle fiber protein expression + 0
              Abnormal muscle fiber-type distribution + 0
              Abnormal sarcomere morphology + 0
              Abnormality of skeletal muscle fiber size + 0
              Angulated muscle fibers 0
              Autophagic vacuoles 0
              Central core regions in muscle fibers 0
              Centrally nucleated skeletal muscle fibers 0
              Deposits immunoreactive to beta-amyloid protein 0
              Fingerprint bodies 0
              Hypertrophied muscle fibers 0
              Increased endomysial connective tissue 0
              Motheaten muscle fibers 0
              Muscle fiber atrophy + 0
              Muscle fiber inclusion bodies + 0
              Muscle fiber necrosis 0
              Muscle fiber splitting 0
              Myelin-like whorls in vacuolated fibers 0
              Necklace skeletal muscle fibers 0
              Perifascicular muscle fiber atrophy 0
              Ragged-red muscle fibers 0
              Rimmed vacuoles 0
              Ring fibers 0
              Skeletal muscle autophagosome accumulation 0
              Spheroid bodies 0
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