A 4-year-old boy is brought to the physician by his parents because he falls a lot, cannot jump, and tires easily Physical examination reveals weakness in the pelvic and shoulder girdles and enlargement of the child’s calf muscles. The serum level of creatine kinase is elevated. A biopsy of calf muscle reveals marked variation in size and shape of muscle fibers. There are foci of muscle fiber necrosis, myophagocytosis, regenerating fibers, and fibrosis. Molecular diagnostic assays performed on muscle biopsy from the patient would show alterations in the length of the primary transcript for which of the following muscle-associated proteins?
Correct Answer: Dystrophin
Description: Dystrophin. Duchenne muscular dystrophy is caused by mutations of a large gene on the short arm of the X chromosome (Xp21). This gene codes for dystrophin, a protein localized to the inner surface of the sarcolemma. Dystrophin links the subsarcolemmal cytoskeleton to the exterior of the cell through a transmembrane complex of proteins and glycoproteins that binds to laminin. Dystrophin-deficient muscle fibers thus lack the normal interaction between the sarcolemma and the extracellular matrix. This disruption may be responsible for the observed increased osmotic fragility of dystrophic muscle, the excessive influx of calcium ions, and the release of soluble muscle enzymes such as creatine kinase into the serum. The other proteins are not altered in patients with Duchenne muscular dystrophy.Diagnosis: Duchenne muscular dystrophy
Category:
Pathology
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