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Key Features

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Essentials of Diagnosis
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  • Progressive degeneration of skeletal and cardiac muscle occurs

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General Considerations
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  • Duchenne muscular dystrophy (DMD)

    • Results from failure of synthesis of the muscle cytoskeletal protein dystrophin

    • The DMD gene is located on the X chromosome, at position Xp21.1-p21.2

    • Approximately 1 in 4000 male children is affected

  • Becker muscular dystrophy (BMD)

    • A less severe phenotype than DMD

    • Results from mutations in the same gene that result in partial expression of the dystrophin protein

  • Evolution of the natural history of dystrophinopathies in females is demonstrating an increased incidence of serious cardiovascular disease, including cardiomyopathy and arrhythmias

  • Large deletions or duplications can be detected in the gene for dystrophin in 65% of cases

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Clinical Findings

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  • In both DMD and BMD, progressive degeneration of skeletal and cardiac muscle occurs

  • Boys with DMD exhibit proximal muscle weakness and pseudohypertrophy of calf muscles by age 5–6 years

  • Patients become nonambulatory by age 13 years

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Diagnosis

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  • Serum creatine kinase levels are markedly elevated

  • Molecular analysis has largely replaced muscle biopsy for diagnostic purposes

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Treatment

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  • Corticosteroids (prednisone/prednisolone or deflazacort)

    • Extend independent ambulation by approximately 2.5 years

    • Preserve respiratory strength and cardiac function into the second decade

    • Instituting steroid treatment between 4 and 8 years, when motor function plateaus or is in decline, appears to have the greatest impact on muscle strength and cardiorespiratory function

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Outcome

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Prognosis
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  • Boys with DMD frequently die in their twenties of respiratory failure and cardiac dysfunction

  • Prognosis for BMD is more variable

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Reference

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Darras  BT, Miller  DT, Urion  DK: Dystrophinopathies. GeneReviews. www.ncbi.nlm.nih.gov/books/NBK1119/.

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