Disease Description (Causes and Symptoms)
- Definition summary: An X-linked recessive genetic disorder and muscle degeneration disease caused by a partial defect in the dystrophin protein. It has a later age of onset and slower progression than the Duchenne type.
- Causes/pathophysiology: Caused by abnormalities in the DMD (dystrophin) gene on Xp21. Most cases involve gene deletions, and many variants preserve the reading frame, allowing some functional dystrophin to be produced; as a result, symptoms are mild or appear later. Approximately one-third of cases arise from mutations without a family history.
- Major symptoms: Mainly proximal muscle weakness (especially in the lower limbs) and muscle atrophy, pseudohypertrophy of the calf muscles, and gait instability. The age at onset is usually 5–25 years, and progression is slow, so loss of the ability to walk may not occur until several decades later. Cardiomyopathy and respiratory muscle weakness are less common than in the Duchenne type but can occur.
- Test findings helpful for diagnosis: Elevated serum CK (an indicator of muscle injury), a myopathic pattern on electromyography (EMG), abnormal size and amount of dystrophin on muscle biopsy, and confirmation of the DMD gene (usually a deletion) by molecular genetic testing (observed in >90% of cases).
Treatment Methods
- Goals: Relieve symptoms, maintain function, prevent complications (cardiac and respiratory), and improve quality of life.
- Drug treatment
- If cardiomyopathy occurs, follow heart failure treatment guidelines, including ACE inhibitors (or ARBs) and beta-blockers.
- Corticosteroids are standard treatment for the Duchenne type, but in the Becker type they should be decided cautiously on an individual basis after considering benefits and adverse effects (there is no general recommendation).
- Supportive treatment, such as analgesics and medications to prevent osteoporosis, depending on symptoms and complications.
- Rehabilitation and supportive therapy
- Physical therapy and appropriate exercise (low-intensity and non-straining; exercises that cause excessive muscle fatigue or sudden muscle contractions are prohibited).
- Stretching to prevent joint contractures and use of customized orthoses (walkers and assistive devices).
- Respiratory rehabilitation and nocturnal noninvasive ventilation when respiratory muscle weakness occurs, if necessary.
- Surgery/procedures
- Heart transplantation is rare, but consultation with a cardiologist is needed in end-stage heart failure.
- Consider orthopedic surgery (tenotomy and joint correction) for long-term deterioration of ambulation and contractures.
- Genetic counseling and prevention
- Explain the pattern of familial transmission (X-linked recessive), carrier testing (female family members), and preconception and prenatal genetic counseling and prenatal diagnosis options.
- Latest developments and clinical trials
- Approved gene therapies specifically for BMD are limited. Because gene-based research and clinical trials (e.g., exon skipping and gene delivery) are focused mainly on the Duchenne type, checking the possibility of clinical trial participation at a specialized center is recommended.
Checkpoints Before an Outpatient Visit (Including Example Questions)
Items and records to prepare (print and bring if possible)
- A list of all medications and supplements currently being taken (including dosage and frequency)
- Previous test results: CK levels, genetic test results (the report, if available), echocardiography and electrocardiogram (ECG) results, and pulmonary function test (PFT) results
- Family history (men with reduced muscle strength, heart failure at a young age, etc.)
- Record of symptom changes: walking distance (e.g., how many meters), difficulties that have developed in daily activities, and symptoms suggesting shortness of breath or sleep apnea (daytime sleepiness and severe snoring)
- Lifestyle information: exercise habits, occupation, and pregnancy plans (for female carriers) Examples of items that are helpful for patients to write down in advance for the outpatient visit (prepare as questions)
- When did the symptoms begin, and what was the first symptom to appear?
- Have there been any changes in function (such as walking or climbing stairs) during the past 6–12 months?
- Is there shortness of breath, nighttime breathing problems, or symptoms of aspiration (difficulty swallowing or frequent coughing)?
Examples of General Questions to Ask the Doctor
- Based on my current condition (diagnostic results), what course of progression can be expected?
- How often should cardiac and respiratory monitoring be performed, and what tests are needed?
- What are the major side effects of the medications I am taking, and what should I be careful about in daily life?
- What specific physical therapy or exercise program do you recommend?
- Is participation in a clinical trial possible, or is additional genetic testing recommended?
Examples of Disease-Specific Questions
- Based on the variant observed in my (or my family member's) genetic test results, what is the exact risk to children (and how does it differ between males and females)? What carrier testing and prenatal diagnosis options are available?
- Based on the current condition of the heart (echocardiography and ECG results), how do you determine when to start cardiac medication and preventive treatment (e.g., whether to recommend starting an ACE inhibitor)?
Additional Information
- During anesthesia and surgery: Patients with muscular dystrophy may face risks (such as hyperkalemia and rhabdomyolysis) when certain anesthetics (e.g., succinylcholine) or some inhalational anesthetics are used. Therefore, be sure to inform the anesthesiologist of the medical history before any planned anesthesia.
- Emergencies: Immediate medical attention is recommended if acute shortness of breath, sudden severe worsening of muscle pain or weakness, or dark brown urine (suspected rhabdomyolysis) occurs.