Becker muscular dystrophy

Overview

Becker muscular dystrophy (BMD) is a form of muscular dystrophy that leads to progressive weakness and breakdown of the skeletal muscles, which are the muscles used for movement. It also often affects the heart muscle. BMD is a genetic condition, meaning it is caused by alterations in a person's DNA. While symptoms can vary significantly between individuals, they generally appear later in childhood or adolescence and progress more slowly compared to a related condition, Duchenne muscular dystrophy [PMID:31536294].

BMD primarily affects males, with an estimated prevalence of about 1 in 18,000 live male births. Females can carry the genetic change but usually do not show significant symptoms, though some may experience mild muscle weakness or heart problems. The condition is named after Dr Peter Emil Becker, who first described it in the mid-20th century.

Symptoms & clinical features

The initial symptoms of Becker muscular dystrophy often involve the muscles of the hips, pelvis, thighs, and shoulders. Individuals may experience difficulty with physical activities such as running, jumping, climbing stairs, or getting up from the floor. Muscle cramps, especially during exercise, can also be an early sign. Over time, the weakness spreads to other muscle groups, including those in the arms and legs.

Unlike Duchenne muscular dystrophy, individuals with BMD typically retain the ability to walk into adulthood, though some may eventually require assistance with mobility. Heart muscle involvement, known as cardiomyopathy, is a common feature of BMD and can occur even before significant skeletal muscle weakness is apparent. It is an important aspect of the condition that requires regular monitoring. Some individuals may also experience learning difficulties or behavioural differences, though these are generally less severe than in Duchenne muscular dystrophy [PMID:24130310].

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Affected organs

The primary organs affected in Becker muscular dystrophy are the skeletal muscles throughout the body, leading to weakness and eventual muscle tissue loss. This particularly impacts the large muscle groups that support movement, such as those in the thighs, hips, shoulders, and upper arms. The diaphragm, a crucial muscle for breathing, can also be affected in later stages, potentially leading to respiratory issues.

A significant organ affected in BMD is the heart. Many individuals with BMD develop cardiomyopathy, a disease of the heart muscle that makes it harder for the heart to pump blood effectively. This can lead to heart failure over time. Regular cardiac monitoring is therefore a critical part of managing BMD. While less common, the smooth muscles of the digestive system can also occasionally be affected, leading to issues like gastrointestinal motility problems.

Brain

Central nervous system involvement

Nervous system

Peripheral nerve involvement

Risks & severity

The severity of Becker muscular dystrophy varies considerably among affected individuals. Some may experience only mild symptoms and remain mobile well into their later years, while others may have more significant muscle weakness and require mobility aids earlier. The age of symptom onset is typically later than in Duchenne muscular dystrophy, often in late childhood, adolescence, or even early adulthood [PMID:31536294].

The progression of muscle weakness is generally slower in BMD compared to Duchenne muscular dystrophy. However, cardiac complications, particularly dilated cardiomyopathy, represent a significant risk and can occur independently of the severity of skeletal muscle weakness. Life expectancy can be reduced due to cardiac or respiratory complications, but with appropriate medical management, many individuals with BMD live well into adulthood and middle age.

Genetic causes

Becker muscular dystrophy is caused by pathogenic variants in the *DMD* gene. This gene is one of the largest known human genes and provides instructions for making a protein called dystrophin. Dystrophin is crucial for the proper functioning and structure of muscle cells.

Within muscle cells, dystrophin acts as a vital structural link, connecting the internal framework of the muscle cell (cytoskeleton) to the outer membrane and the surrounding extracellular matrix. This connection helps to protect muscle fibres from damage during muscle contraction and relaxation. In BMD, pathogenic variants in the *DMD* gene lead to the production of a dystrophin protein that is either abnormal in size or reduced in quantity, but still partially functional. This contrasts with Duchenne muscular dystrophy, where the *DMD* gene variants typically result in a complete absence or non-functional dystrophin, leading to more severe symptoms [PMID:20301309].

• DMD
  dystrophin
  The DMD gene provides instructions for producing dystrophin, a protein essential for maintaining the structural integrity of muscle fibres, particularly in skeletal and heart muscles.

Inheritance pattern

Becker muscular dystrophy is inherited in an X-linked recessive pattern. This means that the *DMD* gene is located on the X chromosome, and a pathogenic variant on this chromosome can lead to the condition. Males have one X and one Y chromosome, so if their single X chromosome carries a pathogenic *DMD* variant, they will develop BMD.

Females have two X chromosomes. If one X chromosome carries a pathogenic *DMD* variant, they are typically carriers and usually do not develop the full condition because their other normal X chromosome can compensate. However, some female carriers may experience mild symptoms such as muscle weakness, cramps, or heart problems. Each son of a female carrier has a 50% chance of inheriting the pathogenic variant and developing BMD, while each daughter has a 50% chance of being a carrier.

Diagnosis & testing

The diagnosis of Becker muscular dystrophy typically begins with a clinical evaluation based on characteristic symptoms like progressive muscle weakness, often observed in early childhood or adolescence. A blood test to measure creatine kinase (CK) levels is often an initial step, as CK levels are usually significantly elevated in individuals with muscular dystrophy due to muscle damage.

Confirmation of BMD is primarily achieved through genetic testing, which looks for pathogenic variants in the *DMD* gene. This testing can involve different methods, such as gene sequencing or deletion/duplication analysis, to identify the specific genetic change. In the UK, genetic testing for muscular dystrophies like BMD is available through the NHS Genomic Medicine Service, often following a referral from a neurologist or paediatrician. Relevant NHS R-codes for muscular dystrophies include R136 (Dystrophinopathy). Occasionally, a muscle biopsy may be performed to examine muscle tissue and assess dystrophin protein levels or structure, although genetic testing is now the preferred diagnostic method.

Management & lifestyle

Management of Becker muscular dystrophy focuses on managing symptoms, preventing complications, and improving quality of life. This typically involves a multidisciplinary team approach, including neurologists, cardiologists, physiotherapists, occupational therapists, and genetic counsellors.

Physical therapy and exercise programmes are often recommended to maintain muscle strength and flexibility, and to prevent contractures. Mobility aids may be introduced as needed. Regular cardiac monitoring, including echocardiograms and electrocardiograms, is essential to detect and manage cardiomyopathy early. Medications such as ACE inhibitors or beta-blockers may be prescribed to support heart function. Respiratory function should also be monitored, and interventions like breathing exercises or nocturnal ventilation may be considered if respiratory muscles become significantly weakened. Emotional and psychological support is also an important aspect of care for individuals and families affected by BMD.

UK care pathway

In the UK, individuals suspected of having Becker muscular dystrophy are typically referred by their GP to a specialist, such as a neurologist or a paediatrician. These specialists can then refer for genetic testing through the NHS Genomic Medicine Service. The testing panel for dystrophinopathies, including BMD, falls under NHS R-code R136, which covers sequencing and deletion/duplication analysis of the *DMD* gene.

Following a confirmed diagnosis, care is usually coordinated through specialist neuromuscular centres. These centres provide access to multidisciplinary teams who can offer comprehensive management and support. Genetic counsellors play a crucial role in explaining the inheritance pattern, discussing the implications for family members, and providing support for reproductive decision-making.

Related conditions

Becker muscular dystrophy belongs to a group of conditions known as dystrophinopathies, which are all caused by pathogenic variants in the *DMD* gene. The most closely related condition is Duchenne muscular dystrophy (DMD). While both are caused by *DMD* gene changes, DMD is generally much more severe, with earlier onset and faster progression of muscle weakness, often leading to loss of ambulation in childhood. This difference in severity is primarily due to the type of *DMD* gene variant and its impact on dystrophin protein function.

Other conditions that might present with similar symptoms of muscle weakness include limb-girdle muscular dystrophies, which are a heterogeneous group of genetic conditions affecting muscles around the hips and shoulders. Differential diagnosis relies heavily on specific genetic testing to identify the causative gene and distinguish between these conditions.

• Duchenne muscular dystrophy
  Neurogenetics
  Shares 1 gene

Frequently asked questions

References

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3. Kamdar F, Garry DJ. Dystrophin-Deficient Cardiomyopathy. Journal of the American College of Cardiology. 2016. PMID: 27230049
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5. Erol Ç. Becker Muscular Dystrophy, Biomarkers and Risk Scores. Anatolian journal of cardiology. 2026. PMID: 42779372
6. Escobar-Huertas JF, Vaca-González JJ, Guevara JM. Duchenne and Becker muscular dystrophy: Cellular mechanisms, image analysis, and computational models: A review. Cytoskeleton (Hoboken, N.J.). 2024. PMID: 38224155
7. Ho R, Nguyen ML, Mather P. Cardiomyopathy in becker muscular dystrophy: Overview. World journal of cardiology. 2016. PMID: 27354892
8. Wein N, Alfano L, Flanigan KM. Genetics and emerging treatments for Duchenne and Becker muscular dystrophy. Pediatric clinics of North America. 2015. PMID: 26022172