Becker Muscular Dystrophy

Becker muscular dystrophy (BMD) is an X-linked recessive genetic disorder that is caused by a mutation in the DMD gene. Abnormal, partially functional muscle dystrophin protein is produced, which leads to progressive muscle weakness and the eventual loss of ambulation. The clinical course is highly variable, but symptoms generally occur by adolescence. The diagnosis is based on muscle enzymes, genetic testing, and muscle biopsy (if necessary). Management of BMD is supportive and aimed at slowing disease progression and complications. Dilated cardiomyopathy is the leading cause of death.

Last update:

Table of Contents

Share this concept:

Share on facebook
Share on twitter
Share on linkedin
Share on reddit
Share on email
Share on whatsapp



Becker muscular dystrophy (BMD) is the 2nd most common form of muscular dystrophy.

  • Almost exclusively seen in boys 
  • Worldwide prevalence: 0.1–1.8 per 10,000 male births


Becker muscular dystrophy is caused by non-frameshift deletion or duplication mutations of the DMD gene on the short arm of the X chromosome.

  • DMD is the largest known protein-coding human gene, which places it at an increased risk for mutations.
  • Most cases are inherited in an X-linked recessive pattern from a carrier mother.
  • Some cases occur from de novo mutations.


Normal physiology:

  • DMD gene encodes for normal dystrophin protein, which is essential for the structural stability of the myofibers.
  • Dystrophin forms a large glycoprotein complex (dystrophin-associated glycoprotein complex):
    • Acts as a mechanical link between the cytoskeleton and the extracellular matrix of muscle 
    • Allows for normal muscle function

Pathophysiology in BMD:

  • A mutation in DMD gene encodes for an abnormal, but partially functional, dystrophin protein.
  • Partially functional dystrophin proteins → partially functional glycoprotein complex → partially functional mechanical links between the cytoskeleton and extracellular matrix of muscle
  • Partial loss of dystrophin proteins → ↑ susceptibility to myofiber damage and necrosis
  • Suboptimal attempts at myofiber regeneration → replacement of muscle with fibrous and adipose tissue

Clinical Presentation


Becker muscular dystrophy has a highly variable presentation.

  • Clinical symptoms may present between 5 and 60 years of age, but most often present by adolescence.
  • Most patients are nonambulatory by approximately 20 years of age.
  • Death often occurs around the age of 40 and is frequently due to dilated cardiomyopathy.
  • Patients with less-severe disease may have a near-normal life span.


Becker muscular dystrophy follows a course of slowly progressive muscle weakness in a proximal-to-distal pattern.


  • Muscle cramping with strenuous activity
  • Difficulty walking and running
  • Difficulty climbing stairs and jumping
  • Easily fatigued
  • Toe walking

Physical exam findings:

  • Hypotonia
  • Hyporeflexia
  • Fasciculations
  • Lumbar lordosis
  • Gower’s sign
    • The use of the arms and hands to maneuver the body to a standing position
    • Due to proximal muscle weakness
  • Calf pseudohypertrophy
    • Large but weak gastrocnemius muscles
    • Caused by replacement of muscle with adipose and fibrous tissue
  • Achilles tendon shortening and contractures


Muscle enzymes

  • ↑ CK 
    • Typically 5–10 times the upper normal limit
    • Peaks at around 10–15 years of age and declines as muscle is replaced by fat and fibrous tissue
  • ↑ Aldolase 
  • ↑ AST and ALT

Genetic testing

  • Sufficient for the diagnosis
  • Evaluating for DMD gene deletions and duplications
  • Techniques:
    • Multiplex ligation-dependent probe amplification (MLPA)
    • FISH
    • PCR

Muscle biopsy

  • Indicated if genetic testing does not confirm a mutation but there is still a high clinical suspicion
  • Findings: 
    • Necrotic muscle fibers of varying sizes
    • Replacement of muscle with fat and fibrous tissue
    • Dystrophin on immunostaining
Histopathological exam of Becker muscular dystrophy

Muscle biopsy in Becker muscular dystrophy:
Histopathological examination shows necrotic muscle fibers with replacement by fibrous and adipose tissue (A). Immunostaining shows partial positivity for dystrophin in Becker muscular dystrohy (B) compared with normal muscle (C).

Image: “Histopathological examination” by Jing Miao et al. License: CC BY 4.0


  • Not commonly used for diagnosis, but can help differentiate BMD from other forms of muscle weakness 
  • Shows small polyphasic potentials

Cardiac screening

  • Electrocardiogram: detects conduction abnormalities  
  • Echocardiogram: assesses for dilated cardiomyopathy


No curative treatment exists for BMD. Management is aimed at supportive and palliative care.

General management

  • Multidisciplinary care is required.
  • Physical therapy
  • Mobility aids
  • Nutritional support

Medical therapy

  • Corticosteroids:
    • Data in BMD are limited.
    • Goal is to slow the progression of muscle weakness.
  • Investigational therapies:
    • Gene therapy
    • Cell therapy

Surgical management

  • Tendon-release surgery for contractures
  • Treatment of scoliosis

Palliative care and advanced planning

  • Patients and families should be informed of the long-term prognosis.
  • Address end-of-life issues.
  • Palliative measures can be used at any point in the disease.


  • Cardiac:
    • Cardiac muscle fibrosis leads to:
      • Dilated cardiomyopathy
      • Conduction abnormalities and arrhythmias
    • Heart failure due to dilated cardiomyopathy is the most common cause of death.
    • Cardiac involvement is more common than in Duchenne muscular dystrophy.
  • Respiratory:
    • Progressive impaired pulmonary function due to:
      • Chest wall and diaphragm muscle weakness
      • Abnormal posture from scoliosis
    • Assisted ventilation may be required.
    • Increased risk for pneumonia
  • Orthopedic:
    • Scoliosis
    • Fractures secondary to falls
    • Contractures
  • Neurocognitive:
    • Intellectual disability
    • Less common than in Duchenne muscular dystrophy

Differential Diagnosis

  • Duchenne muscular dystrophy (DMD): the most common and most severe form of muscular dystrophy. Duchenne muscular dystrophy is due to an X-linked recessive frameshift mutation in the DMD gene, which produces abnormal dystrophin protein. The condition is more severe than BMD, with an earlier onset of symptoms, more rapid clinical progression, and shorter life expectancy. The diagnosis is based on markedly elevated CK, genetic testing, and muscle biopsy. Management is supportive.
  • Facioscapulohumeral dystrophy: an autosomal dominant disorder resulting from mutations in DUX4 or SMCHD1 genes. Both boys and girls are affected. Patients present with progressive weakness of facial, scapular, and muscles of the upper arm by 20 years of age. Cardiac involvement is rare. There is a modest elevation in CK and the diagnosis is confirmed by genetic testing. Management is supportive.
  • Congenital muscular dystrophy: a group of mostly autosomal recessive genetic disorders. Onset is at birth or in early infancy. Symptoms include hypotonia, delayed motor development, progressive muscular weakness, and contractures. Diagnosis is by genetic testing, and management is supportive.
  • Limb-Girdle muscular dystrophy: a group of myopathic disorders resulting from varying genetic defects. Both boys and girls are affected. The time of onset for the disease varies and is characterized by slowly progressive atrophy and weakness of the proximal muscles of the hip and shoulder. Cardiac disease is not typical. Diagnosis is confirmed by genetic testing. Management is supportive.
  • Myotonic dystrophy: a group of autosomal dominant disorders that can affect multiple systems. Myotonic dystrophy can be congenital or adult onset. Findings include myotonia, distal and facial muscle wasting, cataract, intellectual disability, and endocrine disorders. The diagnosis is based on genetic testing, and management is mainly supportive.
  • Emery-Dreifuss muscular dystrophy: a genetic disease with various modes of inheritance. The disease is characterized by slowly progressive weakness of the upper arms and lower legs, contractures, and cardiac abnormalities in the 1st or 2nd decade of life. Modestly elevated CK may be seen. Genetic testing is used to confirm the diagnosis. Management is supportive, and most individuals do not lose the ability to ambulate.
  • Spinal muscular atrophy: a group of autosomal recessive disorders leading to degeneration of the anterior horn cells of the spinal cord and brainstem. The clinical presentation varies. More severe forms of spinal muscular atrophy present in infancy to early childhood with progressive weakness, muscle atrophy, gross motor delay, tongue atrophy and fasciculations, dysphagia, and respiratory insufficiency. Diagnosis is confirmed based on genetic testing. Management is supportive, and life expectancy varies by the disease type.


  1. Nair, D. (2019). Dystrophinopathies. Medcape. Retrieved February 21, 2021, from
  2. National Institutes of Health. (2018). Spinal Muscular Atrophy.
  3. Centers for Disease Control and Prevention. (2020). What is Muscular Dystrophy?
  4. Darras, B.T. (2021). Duchenne and Becker Muscular Dystrophy. UpToDate. Retrieved February 21, 2021, from
  5. Darras, B.T. (2020). Duchenne and Becker muscular dystrophy: Clinical features and diagnosis. In Dashe, J.F. (Ed.), Uptodate. Retrieved February 28, 2021, from
  6. Darras, B.T. (2020). Duchenne and Becker muscular dystrophy: Management and prognosis. In Dashe, J.F. (Ed.), UpToDate. Retrieved February 28, 2021, from

Study on the Go

Lecturio Medical complements your studies with evidence-based learning strategies, video lectures, quiz questions, and more – all combined in one easy-to-use resource.

Learn even more with Lecturio:

Complement your med school studies with Lecturio’s all-in-one study companion, delivered with evidence-based learning strategies.

🍪 Lecturio is using cookies to improve your user experience. By continuing use of our service you agree upon our Data Privacy Statement.