Becker Muscular Dystrophy

Signs and Symptoms

In Becker muscular dystrophy (BMD), the sequence of muscle degeneration typically starts in the hips and pelvic region, extends to the thighs, and then progresses to the shoulders. Individuals with BMD often develop a distinctive manner of walking to counteract muscle weakness; they may adopt a swaying, waddle-like gait, walk on the balls of their feet, or protrude their stomachs. The initial appearance of BMD symptoms can occur at any age between early childhood and late adulthood.

The progression of muscle weakening in BMD can vary significantly from one individual to another. Generally, individuals diagnosed with BMD are able to walk unaided until at least the age of 16, with many maintaining ambulatory capabilities throughout much of their lives.

Pain and Sensation

Muscular dystrophies, such as Becker muscular dystrophy (BMD), primarily affect skeletal muscles—the muscles that are involved in movement—because the condition does not directly impact the nerves, sensation including touch, as well as other senses remain intact. Additionally, control over smooth muscles, which are responsible for involuntary actions in the bladder and bowel, as well as sexual function, is typically preserved.

Muscle deterioration in BMD generally does not cause pain directly. However, muscle cramps can occur, which some individuals with BMD might experience. When cramps do arise, they are often manageable with over-the-counter pain medications. It’s always recommended to consult with a healthcare provider before starting any new medication, even over-the-counter drugs, to ensure they are safe and appropriate for your specific health condition.

The heart

Heart muscles, like the muscles in limbs, can also suffer from the absence of dystrophin. A majority of individuals with Becker muscular dystrophy (BMD) eventually face cardiomyopathy, a condition marked by the weakening of the heart muscle, as a result of dystrophin shortage. This leads to a deterioration of the myocardium, the muscular layer of the heart, analogous to the decline observed in skeletal muscles.

Typically, those diagnosed with BMD initially exhibit signs of muscle weakness prior to any indication of heart issues. Nevertheless, a few exceptional cases documented in medical studies report the emergence of cardiac symptoms before any muscular weakness. Electrocardiography tests reveal cardiac involvement in a significant proportion — 60% to 70% — of BMD cases, which in some instances can be a prominent aspect of the disease. This condition can affect all four chambers of the heart, with fibrosis leading to potentially rapid heart failure.

The cardiac complications associated with BMD can pose a serious risk to life, sometimes as early as during teenage years. There are instances where patients with BMD experience only mild skeletal muscle symptoms yet suffer from critical heart conditions. There is a notion that high-intensity exercise, while generally possible for BMD patients, might actually exacerbate the condition of the cardiac muscle cells that contain defective dystrophin. Due to these factors, it is advised that all individuals with BMD undergo regular cardiac evaluations.

Breathing and coughing

In Becker muscular dystrophy (BMD), the muscles responsible for respiration typically retain their strength for an extended period, but over time, they may gradually weaken. When this occurs, it can compromise the effectiveness of breathing and the ability to cough, which is essential for clearing mucus and other secretions from the airways.

Cognition

Medical professionals suggest that anomalies in dystrophin within the brain might be the root of cognitive and behavioral deficits, as well as various neuropsychiatric disruptions. In individuals with Becker muscular dystrophy (BMD), intellectual disabilities or cognitive impairments are generally less frequent and less profound than in those with Duchenne muscular dystrophy (DMD). It’s estimated that around 10% of BMD patients have an IQ below 70, indicating a lower incidence of significant cognitive challenges in BMD compared to DMD.

Causes:

Genes act as blueprints for proteins, which are crucial components in all living organisms. Becker muscular dystrophy (BMD) arises due to a mutation in the dystrophin gene located on the X chromosome, which leads to the production of insufficient amounts of functional dystrophin protein. In individuals with BMD, the dystrophin that is produced by muscle cells is structurally flawed, causing it to function improperly. Dystrophin’s role is to maintain the integrity of muscle cells; without it, muscle cells become delicate and are more prone to damage.

In cases of BMD, a truncated version of dystrophin is still produced, retaining partial functionality. This presence of partially working dystrophin means that the muscles in BMD patients do not deteriorate as severely or rapidly as they do in those with Duchenne muscular dystrophy (DMD), where there is a complete lack of functional dystrophin.

Inheritance in BMD

Becker muscular dystrophy (BMD) can be present in a family even if only a single individual is known to have the condition, due to the patterns of genetic inheritance. BMD is passed down in an X-linked recessive manner, which means the mutation responsible for the condition is located on the X chromosome.

Since males have one X chromosome and one Y chromosome, a son receiving the X chromosome with the dystrophin mutation from his mother will have BMD. He inherits the Y chromosome from his father, which determines his male sex but does not carry the dystrophin gene. Daughters, on the other hand, inherit two X chromosomes, one from each parent. If a daughter inherits the mutated gene from her mother, she becomes a carrier of BMD. She has a 50% chance of passing the mutated gene to her offspring. Although carriers often do not show symptoms of the disease, they are at an increased risk of developing cardiomyopathy.

A family with no apparent history of BMD may have a child with the condition due to several reasons:

1. The mutation causing BMD could have been silently passed down through female carriers in the family for generations. If no males were born with the mutation, or the condition was not properly identified in the past, the family may not have been aware of its presence.
2. Another explanation is the occurrence of a de novo mutation, meaning a new mutation arises spontaneously in the mother’s egg cell that is transmitted to the child. Since this type of mutation is not present in the mother’s blood, it would not be detected in routine carrier screenings, which could explain the unexpected emergence of BMD in the child.

Diseases inherited in an X-linked recessive pattern mostly affect males, because a second X chromosome usually protects females from showing symptoms.

If a mother has one child with Becker muscular dystrophy (BMD), it may indicate that she carries a mutation in one of her dystrophin genes, suggesting a risk that she could pass this mutation to additional children. If a son is born with BMD, he inherited the mutation from his mother. If a daughter is born without BMD, she might still be a carrier of the mutated gene and could potentially pass it on to her own children.

A man with BMD does not pass the disorder to his sons, as they receive his Y chromosome, which does not carry the BMD gene. However, his daughters will always receive his X chromosome, which contains the BMD mutation, making them carriers. As carriers, his daughters have a 50% chance of passing the mutation to each of their children, with sons having a chance of being affected by BMD and daughters having a chance of being carriers.

Families affected by BMD are encouraged to seek information on their specific inheritance pattern and risks by consulting with a medical professional at an MDA Care Center or a genetic counselor, who can provide personalized guidance based on the family’s genetic history.

Diagnosis

The process of diagnosing Becker muscular dystrophy (BMD) can greatly differ since symptoms may manifest as early as age 5 or as late in life as age 60. Some individuals with BMD may not achieve developmental milestones on time, or they may discover physical limitations during activities such as physical education classes or military exercises.

To diagnose BMD or any other type of muscular dystrophy, a physician typically begins with a comprehensive review of the patient’s medical history and a thorough physical examination. This preliminary assessment can provide significant insights that guide the diagnosis even before any advanced diagnostic procedures are undertaken.

A critical part of the diagnostic process is to discern whether the observed muscle weakness is due to a defect in the muscles or in the nerves that control muscular movements. Weakness can also arise from issues in the motor neurons, which are nerve cells in the spinal cord and brain that connect to muscles throughout the body; such issues can mimic muscle-related problems.

BMD can present symptoms that overlap with other conditions such as Duchenne muscular dystrophy (DMD) or limb-girdle muscular dystrophy (LGMD), which makes an accurate diagnosis challenging and necessitates a thorough evaluation, often including genetic testing.

One of the early tests in diagnosing muscle diseases is measuring creatine kinase (CK) levels in the blood. CK is an enzyme that escapes from damaged muscle tissue. High levels of CK typically indicate muscle damage from a condition like muscular dystrophy. Elevated CK levels can signal that muscle deterioration is the source of the weakness, though it doesn’t specify the exact muscle disorder. In males with BMD, CK levels are generally significantly higher than normal, while carrier females may have CK concentrations ranging from mildly to substantially elevated.

For a definitive diagnosis, genetic testing is performed, including dystrophin gene deletion analysis through methods like Multiplex ligation-dependent probe amplification (MLPA), fluorescence in situ hybridization (FISH), and polymerase chain reaction (PCR), with MLPA being a commonly used technique. These tests can detect specific gene mutations or deletions associated with BMD, providing clarity on the diagnosis.

In some instances, when Becker muscular dystrophy (BMD) is suspected, a physician may order an electromyography (EMG) test. This procedure involves inserting needles with electrodes into the muscle to deliver small electrical currents and measure the muscle’s electrical activity, providing insight into the muscle’s health and function.

Another diagnostic tool is a muscle biopsy, which entails extracting a small piece of muscle tissue, typically from the thigh, to evaluate dystrophin levels. Absent dystrophin indicates Duchenne muscular dystrophy (DMD), while reduced levels suggest BMD.

Nerve conduction studies are usually performed to rule out nerve disorders, with normal results expected in cases of BMD. Additionally, heart function may be assessed using an electrocardiogram (EKG) or echocardiogram, and pulmonary function tests may be conducted to evaluate respiratory capacity.

X-rays may be necessary to identify bone complications that can arise from muscle contractures and wasting, such as scoliosis. Liver function tests, including transaminase levels, may also be part of the evaluation to exclude other causes of muscle damage.

Cardiac MRI can provide detailed images of the heart, allowing for the assessment of muscle damage and dysfunction related to cardiomyopathy, a common cardiac manifestation in BMD patients.

DNA testing for the dystrophin gene mutation from a blood sample is widely available and can often distinguish BMD from DMD with high accuracy, especially when clinical signs and elevated CK levels point towards a dystrophinopathy. The genetic testing primarily includes deletion/duplication analysis, which can detect the mutations responsible for 70% to 80% of cases, and sequence analysis for point mutations.

The Western blot test is another laboratory technique used to measure the quantity and size of dystrophin protein, providing additional details on the extent of muscle involvement.

For female relatives of individuals with BMD, DNA testing can determine carrier status. Identifying carriers is essential, as they have a 50% probability of passing the gene mutation to their offspring, who may then either be carriers or have BMD.

Other Treatment

Since Becker muscular dystrophy (BMD) currently has no cure, treatment efforts are centered on symptom management and slowing the progression of the disease. As BMD advances, patients may face emergencies stemming from cardiac and respiratory complications, which are indicators of the disease’s progression. Research into potential future treatments for BMD is ongoing and includes several promising avenues:

• Gene therapy may eventually lead to effective treatment, given proper identification of the gene defect and effective administration of the corrective gene to the muscle targets.
• Myoblast treatment, as well as the use of stem cells, also may be alternative modalities if proven successful.
• Steroids have been reported to show benefit in patients with DMD, but there are conflicting reports. There is no conclusive proof that steroids have a beneficial effect on Becker muscular dystrophy.

Differential Diagnosis

It is critical to accurately differentiate Becker muscular dystrophy (BMD) from other conditions that manifest primarily with muscle weakness.

Duchenne Muscular Dystrophy (DMD) is a more severe pathology with an earlier onset compared to BMD. Patients with DMD typically become dependent on a wheelchair at a younger age and have a reduced lifespan. A notable characteristic is a lower concentration of the protein dystrophin in these individuals.

In the case of Polymyositis, this idiopathic inflammatory myopathy is notable for symmetrical weakness in the muscles close to the body’s center, which could be mistaken for BMD. However, the lack of muscle enlargement often seen at the distal ends of the limbs in BMD aids in setting them apart.

Spinal Muscular Atrophy, an inherited autosomal-recessive condition, presents with reduced reflexes, muscle twitches of the tongue, and weakness in the muscles controlled by the cranial nerves, with comparatively fewer cognitive deficits. The lack of mutations in the dystrophin gene, confirmed by DNA testing, points towards this diagnosis instead of BMD.

Differentiating Limb-girdle Muscular Dystrophy from BMD is challenging; however, the characteristic calf muscle enlargement seen in BMD is not present in this condition.

Dilated Cardiomyopathy is a grave complication often seen in patients with muscular dystrophy and is a leading cause of death. Nevertheless, it can also occur independently, due to a variety of other genetic or non-genetic causes.

With Emery-Dreyfuss Muscular Dystrophy, the presence of early joint contractures and heart issues are distinguishing features, alongside muscle wasting and weakness in the humeroperineal distribution which begins in the early decades of life, setting it apart from BMD.

Myasthenia Gravis can imitate BMD due to fluctuating weaknesses in skeletal muscles; however, symptoms like facial muscle weakness, drooping eyelids, and double vision are more prominent, although sometimes it may present with only proximal muscle weakness.

Lastly, Metabolic Myopathies, which are a group of storage diseases caused by enzyme deficiencies affecting the metabolism of glycogen, lipids, and mitochondria, usually trigger muscle weakness and pain during exercise rather than at rest, differing from the muscle weakness pattern observed in BMD.

Treatment and Management

Currently, there is no cure for Becker muscular dystrophy; however, medical professionals employ a variety of management strategies to alleviate symptoms and support mobility:

– Orthotic devices such as ankle or foot braces are commonly prescribed, and assistive mobility equipment like scooters and wheelchairs can greatly aid patients in their daily activities.

– Pharmacological interventions are available for cardiac complications that often accompany this condition.

– Continuous cardiac evaluation is essential to track the progression of any heart-related issues.

– In instances of advanced cardiomyopathy, surgical intervention or even a heart transplant may be necessary to address severe cardiac dysfunction.

Occupational Therapy

Modifications to Activities of Daily Living (ADL) can be tailored according to the extent of impairment experienced by individuals. By incorporating assistive devices, individuals can maintain independence and ease in their daily routines. Tools such as dressing sticks, strategically installed grab bars, adapted dining sets, custom grips, and elevated toilet seats can significantly enhance functionality and safety. For those confined to wheelchairs, positioning essential items at an accessible height is an important adjustment that facilitates ease of access and autonomy.

Orthosis

Addressing mobility issues is a crucial aspect of managing conditions that impair movement. This involves evaluating the need for mobility aids and providing the appropriate devices. A scooter or a customized wheelchair, complete with a tailored seat and back, individualized supports, and electric power, can be instrumental in enhancing the mobility and independence of individuals with such concerns. These personalized mobility solutions are designed to meet the specific needs of the user, ensuring comfort, ease of use, and improved access to various environments.

Speech Therapy

Concerns related to dysphagia, or difficulty swallowing, can be thoroughly assessed by a speech therapist. This specialist may conduct a clinical evaluation to understand the individual’s specific challenges with swallowing. Based on the findings, the therapist might recommend avoiding certain types of food textures or liquid consistencies that could pose a risk. Additionally, they may suggest specific positions or strategies to use during eating and drinking to facilitate safer swallowing and reduce the risk of aspiration. These tailored recommendations are aimed at ensuring adequate nutrition while minimizing the potential complications associated with dysphagia.

Recreational Therapy

Encouraging avocational pursuits, desires, and hobbies is an important strategy for enhancing the well-being and overall physical health of individuals with conditions like Becker muscular dystrophy. It’s vital to consider the child’s interests and abilities when choosing activities. Engaging in music, dance, crafts, art, or yoga can be both enjoyable and beneficial, potentially aiding in the maintenance of muscle function and mental health.

However, healthcare providers need to exercise caution with the use of anesthesia in individuals with Becker muscular dystrophy due to the increased risk of complications. Anesthetic agents must be chosen and administered carefully, and the patient should be monitored closely throughout any medical procedure requiring sedation.

Complications

Complications associated with conditions like Becker muscular dystrophy can be diverse and may include:

– Cardiomyopathy, which can lead to heart failure, as well as progressive loss of pulmonary and liver functions. The loss of the ability to walk, cognitive impairment, and an increased risk of bone fractures are also potential complications.

– A heightened risk of chest infections following surgical procedures, which can be exacerbated by the compromised respiratory function that often accompanies muscular dystrophies.

– Rhabdomyolysis, a serious syndrome resulting from the rapid breakdown of muscle, which can lead to myoglobinuria condition where muscle proteins are released into the bloodstream, potentially causing kidney failure.

– The prolonged use of corticosteroids as part of the treatment regimen can result in adrenal insufficiency, where the adrenal glands do not produce adequate steroid hormones, and can also lead to a suppressed immune system, increasing the risk of infections.

Close monitoring and proactive management of these complications are essential to improving quality of life and outcomes for individuals with this condition.

Prognosis

Patients diagnosed with Becker muscular dystrophy (BMD) typically experience a clinical course that is less severe and slower in progression compared to those with Duchenne muscular dystrophy (DMD). Despite the progressive nature of BMD, which can lead to a decline in survival over time, the implementation of supportive interventions plays a crucial role in extending the lifespan of affected individuals. The life expectancy for someone with BMD is generally estimated to be around 40 to 50 years.

Prevention

Becker muscular dystrophy (BMD) is indeed an inherited disorder, and there are no preventive measures for the condition itself because it is determined by one’s genetic makeup. If you are living with BMD or if there are concerns about the possibility of passing BMD or other hereditary disorders to offspring, it is advisable to seek the expertise of a healthcare provider or a genetic counselor. A genetic counselor can provide comprehensive information on the risks of hereditary conditions and discuss the available options, including genetic testing and family planning considerations, to help make informed decisions before conceiving a biological child.

Living With

For individuals with Becker muscular dystrophy (BMD), receiving regular, comprehensive medical care is crucial for preventing or managing complications related to the heart and respiratory system. Joining a support group can also be beneficial as it provides a community of peers who understand the challenges associated with BMD.

For caregivers, it’s critical to advocate for the person with BMD to ensure they receive optimal medical care, along with access to mobility aids and therapeutic services that promote independence.

Regarding when to see a healthcare provider, if you or your child has been diagnosed with BMD, it’s important to maintain regular appointments with your healthcare team. These consistent visits allow for the necessary treatments to be administered and for close monitoring of the condition’s progression. Your medical team can give you a tailored schedule for these visits based on the specifics of the diagnosis and individual health needs.

What is the difference between Becker muscular dystrophy and Duchenne muscular dystrophy

Both Becker muscular dystrophy (BMD) and Duchenne muscular dystrophy (DMD) arise from mutations in the dystrophin gene, which is vital for maintaining muscle function. In DMD, this mutation results in the absence of dystrophin in the muscles, leading to a severe and rapidly progressing condition. In BMD, the mutation allows for some production of dystrophin, but not at normal levels, which is why BMD progresses more slowly and is generally less severe than DMD.

BMD is indeed less common than DMD, and while the symptoms may be similar between the two—such as muscle weakness and difficulty with walking—those with BMD typically experience a slower onset and progression of these symptoms. Because of the presence of some dystrophin, muscles in BMD patients deteriorate at a slower rate, leading to a better overall prognosis and a longer life expectancy than is typical with DMD.