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Progressive muscular dystrophies

Last updated: November 18, 2020

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Muscular dystrophies are a group of progressive diseases that affect the musculoskeletal system. Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) are X-linked recessive diseases, whereas limb-girdle muscular dystrophy (LGMD) may be either autosomal dominant or recessive, and facioscapulohumeral dystrophy (FSHD) is usually autosomal dominant. Muscular dystrophies are commonly due to mutations involving muscular genes (e.g., dystrophin-protein coding gene). Patients typically present with muscular complaints affecting specific muscle groups, particularly the pelvic girdle musculature. DMD is the most severe form of muscular dystrophy, with disease onset typically occurring at two to three years of age. BMD usually does not become evident before the age of 15. DMD progresses rapidly and typically leads to ambulatory inability by age 12. Diagnosis of DMD and BMD is established based on blood tests that show increased creatinine kinase, whereas diagnosis of LGMD and FSHD is mainly based on genetic analysis. Treatment of muscular dystrophies is usually supportive and includes physiotherapy, assistive devices (e.g., wheelchair), and psychological support. The life expectancy for patients with DMD is approx. 30 years, whereas patients with BMD and LGMD have a longer life expectancy.

  • Incidence
    • DMD: 1/3500
    • BMD: 1/30,000
  • Sex: : only male individuals affected in DMD and BMD
  • Age of onset
    • DMD: 2–5 years
    • BMD: adolescence or early adulthood, usually > 15 years

References:[1][2][3]

Epidemiological data refers to the US, unless otherwise specified.

References:[2]

  • Dystrophin protein: anchors the cytoskeleton of skeletal and cardiac muscle cells to the extracellular matrix by connecting cytoskeletal actin filaments to membrane-bound α- and β-dystroglycan, which are connected to extracellular laminin
  • Dystrophin gene: largest known protein-coding gene in the human DNA
    • Because of its size, the dystrophin gene is at increased risk for spontaneous mutations.
    • Mutations affecting the dystrophin gene→ alterations of dystrophin protein structure → partial (BMD) or almost complete (DMD) impairment of protein function disturbance of numerous cellular signaling pathways → necrosis of affected muscle cells → replacement with connective tissue and fatty tissue → affected muscles are weak even though they appear larger (“pseudohypertrophy”)

Duchenne is caused by Deleted Dystrophin.

Duchenne muscular dystrophy (DMD)

Becker muscular dystrophy (BMD)

  • Symptoms similar to those of DMD, but less severe
  • Slower progression (patients often remain ambulatory into adult life)
  • Heart involvement is more common compared to DMD.

Becker is Better.”

References:[1]

References:[1]

Facioscapulohumeral muscular dystrophy (FSHD) [4]

  • Definition: a complex genetic disorder characterized by progressive muscle weakness of the face, scapula, upper arm
  • Etiology
    • Inheritance: autosomal dominant (70–90%) or sporadic
    • Deletion of D4Z4 repeat units, each of which contains a copy of a double homeobox protein 4 gene (DUX4), in the 4q35 region
  • Epidemiology: the third most common type of muscular dystrophy
  • Clinical features
    • Progressive muscle weakness
      • Onset usually in childhood and adolescence
      • Asymmetrical involvement
      • Affects the face, scapula, and upper arms
      • Less commonly, the girdle and/or lower leg can be involved
    • Extramuscular manifestations: retinal vasculopathy, hearing loss
  • Diagnosis: genetic testing to detect the D4Z4 short repeat array

Limb-girdle muscular dystrophy (LGMD) [5]

Other

The differential diagnoses listed here are not exhaustive.

References:[6]

  • DMD
    • Life expectancy is approx. 30 years.
    • Cardiac or respiratory failure is usually the cause of death.
  • BMD
    • Life expectancy is 40–50 years.
    • Cardiac failure is typically responsible for the reduced life expectancy.

References:[6]

  1. Darras BT. Clinical features and diagnosis of Duchenne and Becker muscular dystrophy. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. https://www.uptodate.com/contents/clinical-features-and-diagnosis-of-duchenne-and-becker-muscular-dystrophy#H23.Last updated: January 21, 2016. Accessed: February 14, 2017.
  2. Duchenne and Becker muscular dystrophy. https://ghr.nlm.nih.gov/condition/duchenne-and-becker-muscular-dystrophy. Updated: November 1, 2016. Accessed: March 1, 2017.
  3. Becker muscular dystrophy. http://www.orpha.net/consor/cgi-bin/OC_Exp.php?Expert=98895. Updated: September 1, 2009. Accessed: March 1, 2017.
  4. Hamel J, Tawil R. Facioscapulohumeral Muscular Dystrophy: Update on Pathogenesis and Future Treatments. Neurotherapeutics. 2018; 15 (4): p.863-871. doi: 10.1007/s13311-018-00675-3 . | Open in Read by QxMD
  5. Liewluck T, Milone M. Untangling the complexity of limb-girdle muscular dystrophies.. Muscle Nerve. 2018; 58 (2): p.167-177. doi: 10.1002/mus.26077 . | Open in Read by QxMD
  6. Darras BT. Treatment of Duchenne and Becker muscular dystrophy. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. https://www.uptodate.com/contents/treatment-of-duchenne-and-becker-muscular-dystrophy?source=see_link.Last updated: February 10, 2017. Accessed: February 14, 2017.