What are the types of muscular dystrophy?

Types of Muscular Dystrophy

Muscular dystrophies are a group of inherited genetic disorders characterized by progressive muscle weakness and degeneration, with various types affecting different muscle groups and having distinct genetic causes and clinical presentations. 1

Major Types of Muscular Dystrophy

Dystrophinopathies

• Duchenne Muscular Dystrophy (DMD)

  • X-linked disorder affecting approximately 1 in 5,000 live male births 1
  • Caused by mutations in the dystrophin gene leading to absence of dystrophin protein
  • Presents in early childhood with progressive proximal muscle weakness
  • Associated with significant cardiomyopathy and respiratory failure
  • Without supportive care, death typically occurs in late teens or early twenties 1

• Becker Muscular Dystrophy (BMD)

  • Milder variant of dystrophinopathy with partial dystrophin expression
  • Later onset and slower progression than DMD
  • Variable cardiac involvement 1, 2

Myotonic Dystrophies

• Myotonic Dystrophy Type 1 (DM1)

  • Autosomal dominant disorder caused by CTG repeat expansion
  • Characterized by myotonia (delayed muscle relaxation), muscle weakness, and multisystem involvement
  • Cardiac conduction defects common 1, 2

• Myotonic Dystrophy Type 2

  • Similar to DM1 but generally milder with later onset 2

Facioscapulohumeral Muscular Dystrophy (FSHD)

• Typically affects face, shoulder girdle, and upper arms
• Autosomal dominant inheritance
• Variable progression and severity 1, 2

Limb-Girdle Muscular Dystrophies (LGMD)

• Heterogeneous group with multiple subtypes
• Primarily affects shoulder and pelvic girdles
• Can be autosomal dominant (type 1) or recessive (type 2)
• Cardiac involvement varies by subtype 1
• Some forms (types 2C, 2F, and 2I) present primarily as non-ischemic cardiomyopathy 1

Emery-Dreifuss Muscular Dystrophy (EDMD)

• Characterized by early contractures, slowly progressive muscle weakness, and cardiac involvement
• X-linked, autosomal dominant, or autosomal recessive inheritance
• Associated with Lamin A/C mutations in some forms
• High risk of sudden cardiac death due to conduction defects and arrhythmias 1
• ICD placement may be indicated for primary prevention 1

Congenital Muscular Dystrophies

• Present at birth or early infancy
• Multiple subtypes with varying severity
• Often associated with brain and eye abnormalities
• Some forms have significant cardiac involvement 1

Other Types

• Oculopharyngeal Muscular Dystrophy

  • Late-onset disorder affecting eyelid and throat muscles
  • Minimal cardiac involvement 1

• Distal Muscular Dystrophies

  • Primarily affect distal limb muscles (hands, forearms, lower legs)
  • Various genetic causes 2

Clinical Significance and Management

Cardiac Involvement

• Varies significantly between different types of muscular dystrophy
• Some types primarily cause cardiomyopathy (DMD, BMD, some LGMDs)
• Others primarily cause conduction defects and arrhythmias (EDMD, LGMD1B, DM1)
• Some affect both (Barth syndrome, myofibrillar myopathies) 1
• Regular cardiac monitoring is essential in most forms 1

Genetic Testing

• Critical for definitive diagnosis and genetic counseling
• Allows for precise subtype classification
• Guides cardiac surveillance and management strategies
• May identify candidates for emerging gene-specific therapies 1

Monitoring Recommendations

• Regular cardiac assessment is recommended even in asymptomatic patients with muscular dystrophy 1
• ICD placement should be considered in high-risk subtypes such as EDMD and LGMD1B 1
• Primary and secondary prevention ICDs are recommended for patients with neuromuscular disorders using the same indications as for non-ischemic cardiomyopathy if meaningful survival greater than 1 year is expected 1

Diagnostic Approach

• Muscle biopsy remains an important diagnostic tool for distinguishing inflammatory from non-inflammatory myopathies 1
• Genetic testing is increasingly the gold standard for definitive diagnosis 1
• Electromyography helps confirm myopathic processes and target muscles for biopsy 1
• Cardiac imaging (echocardiography, cardiac MRI) is important for detecting cardiac involvement 1

The prevalence of different muscular dystrophy types varies by population, with Duchenne dystrophy, limb-girdle dystrophy, and Becker dystrophy being among the most common forms in many populations 3.