Becker’s Muscular Dystrophy (BMD) is a progressive genetic disorder that causes the voluntary muscles to weaken and waste away over time. It primarily affects the muscles used for movement. BMD progresses slower and is generally milder than Duchenne Muscular Dystrophy (DMD), though both share a common genetic root. This article provides an overview of the underlying cause, typical symptoms, diagnostic steps, and long-term management strategies for BMD.
The Genetic Basis of Becker’s Muscular Dystrophy
Becker’s Muscular Dystrophy is caused by a mutation in the X-linked DMD gene, which provides instructions for making the protein called dystrophin. Dystrophin is a large protein that stabilizes and protects muscle fibers during contraction. The mutation in BMD typically results in a partially functional or reduced amount of dystrophin being produced.
This mutation is often an “in-frame” deletion. This means that while a segment of the gene’s code is missing, the remaining code can still be read to create a shortened, but somewhat working, dystrophin protein. This differs from Duchenne Muscular Dystrophy, where the mutation is usually “out-of-frame,” leading to a complete absence or non-functional version of the protein. The presence of partially functional dystrophin explains why BMD is less severe and progresses more slowly than DMD.
Because the DMD gene is located on the X chromosome, BMD is inherited in an X-linked recessive pattern and almost exclusively affects males. Males inherit one X chromosome, so a single mutated gene is enough to cause the condition. Females, who have two X chromosomes, are typically carriers and usually do not experience symptoms because their second, healthy X chromosome produces functional dystrophin.
Symptoms and Disease Progression
The symptoms of Becker’s Muscular Dystrophy generally begin later, often appearing in late childhood, adolescence, or even early adulthood, with onset varying widely between 5 and 60 years. The initial physical signs involve muscle weakness that starts in the proximal muscles—those closest to the center of the body, particularly the hips, pelvis, and thighs.
Individuals may first notice difficulty with activities such as climbing stairs, running, or getting up from the floor without support (Gower’s sign). A waddling gait and muscle cramps, particularly after exercise, are also common early indicators. The muscle weakness progresses slowly, eventually extending to the shoulder girdle and arms. Many people retain the ability to walk well into their 40s or later.
Involvement of the heart muscle, called cardiomyopathy, is a serious long-term complication of BMD. This weakening of the heart’s ability to pump blood can occur even before significant skeletal muscle symptoms are apparent. Cardiomyopathy is a major factor in the long-term outlook and requires regular monitoring and specialized care.
Diagnostic Procedures
The diagnosis of Becker’s Muscular Dystrophy begins with a physical examination and a review of the patient’s and family’s medical history to note the pattern of muscle weakness and symptom progression. This initial assessment helps distinguish BMD from other muscle-wasting disorders. The physician often orders a blood test to check the levels of creatine kinase (CK), an enzyme that leaks into the bloodstream when muscle tissue is damaged.
In individuals with BMD, CK levels are elevated, often ranging from five to one hundred times the normal limit, indicating a muscle problem. While elevated CK levels point toward a muscular dystrophy, they do not specify the type, making genetic testing the definitive diagnostic tool. Genetic testing involves DNA sequencing of the DMD gene to identify the specific mutation, such as an in-frame deletion or duplication.
Identifying the precise gene change confirms the diagnosis and is necessary for establishing the long-term prognosis. Although less common due to advancements in genetic testing, a muscle biopsy may still be performed in some cases. A biopsy involves taking a small muscle sample to analyze the amount and structure of the dystrophin protein present, which supports the diagnosis.
Current Management and Long-Term Outlook
While there is no cure for Becker’s Muscular Dystrophy, management focuses on a multidisciplinary approach to control symptoms. Supportive therapies are used to maintain function and independence:
- Physical therapy (PT) to maintain muscle strength and flexibility.
- Occupational therapy (OT) to assist with daily tasks.
- Interventions to slow the development of joint contractures.
- Strategies to prolong the ability to walk.
Medical management includes medications aimed at protecting the heart, as cardiomyopathy is a frequent and serious complication. Angiotensin-converting enzyme (ACE) inhibitors and beta-blockers are commonly prescribed to manage heart weakness and delay the progression of heart failure, even in patients without cardiac symptoms. Corticosteroids, such as prednisolone, may be used in some cases to help preserve muscle function, though their use is less standard than in DMD.
The long-term outlook for individuals with BMD is variable but is generally much better than for those with more severe forms of muscular dystrophy. Most people with BMD survive well into mid-to-late adulthood, with life expectancy largely dependent on the severity of cardiac involvement. Regular cardiac monitoring is required to detect and treat heart problems early. This monitoring includes echocardiograms and electrocardiograms. Ongoing, coordinated care from a team of specialists, including cardiologists and neurologists, is necessary for maintaining long-term health and function.