Medicine – Becker Muscular Dystrophy

Becker muscular dystrophy (BMD) is an inherited X-linked recessive muscular dystrophy caused by abnormalities in the dystrophin protein. It is closely related to Duchenne muscular dystrophy (DMD), but the dystrophin abnormality is usually less severe, so the disease presents later and progresses more slowly.

1. Inheritance

Becker muscular dystrophy is inherited in an X-linked recessive pattern.

Therefore, it mainly affects males, while females are usually carriers, although some female carriers can develop muscle weakness or cardiac involvement.

The abnormal gene is the DMD gene on the X chromosome, which encodes dystrophin.

2. Dystrophin Abnormality

Dystrophin is a structural protein that helps connect the muscle-cell cytoskeleton to the surrounding extracellular matrix.

It stabilises the muscle membrane during contraction.

In Becker muscular dystrophy, dystrophin is usually reduced in quantity or abnormal in structure, but some functional protein remains.

This is the major reason BMD is milder than Duchenne muscular dystrophy.

3. Comparison with Duchenne Muscular Dystrophy

The key molecular distinction is:

Duchenne muscular dystrophy → dystrophin is essentially absent or severely deficient.

Becker muscular dystrophy → dystrophin is present but reduced or abnormal.

Because Becker patients retain some functional dystrophin, muscle-cell damage progresses more slowly.

4. Later Age of Onset

Becker muscular dystrophy generally manifests later than Duchenne muscular dystrophy.

Symptoms may begin in later childhood, adolescence, or occasionally adulthood.

This contrasts with Duchenne muscular dystrophy, which usually becomes clinically apparent in early childhood.

5. Milder Clinical Course

BMD generally causes a milder and more slowly progressive muscular dystrophy than DMD.

Patients often remain independently ambulant for much longer.

However, severity varies considerably, and some patients can still develop major skeletal-muscle, respiratory, or cardiac complications.

6. Muscle Weakness

The typical pattern is progressive proximal muscle weakness, especially involving the pelvic girdle and lower limbs.

Patients may develop difficulty:

Running.

Climbing stairs.

Getting up from the floor.

Rising from a chair.

Walking long distances.

Weakness generally progresses more slowly than in DMD.

7. Gowers Sign

Patients with significant proximal lower-limb weakness may demonstrate Gowers sign.

When rising from the floor, the patient uses the hands to “climb up” the thighs because the hip and thigh muscles are weak.

Gowers sign is not specific to Becker muscular dystrophy, but it is characteristic of proximal muscular weakness.

8. Calf Pseudohypertrophy

Calf pseudohypertrophy may occur.

The calves appear enlarged, but the enlargement is partly due to replacement of muscle tissue by fat and connective tissue, rather than true increase in functional muscle mass.

This finding is seen in both Becker and Duchenne muscular dystrophy.

9. Serum Creatine Kinase

Serum creatine kinase (CK) is usually markedly elevated because damaged skeletal muscle releases CK into the bloodstream.

An elevated CK may be detected even before severe clinical weakness develops.

However, CK levels alone cannot distinguish Becker from Duchenne muscular dystrophy.

10. Cardiac Involvement

Cardiac disease is an important complication of Becker muscular dystrophy.

Patients may develop dilated cardiomyopathy and cardiac rhythm abnormalities.

Importantly, the severity of cardiac disease does not always parallel the severity of skeletal-muscle weakness.

Therefore, even relatively mobile patients may require regular cardiac surveillance.

11. Female Carriers and the Heart

Female carriers of dystrophin mutations can occasionally develop cardiomyopathy, even when skeletal-muscle symptoms are minimal or absent.

This is why carrier identification and appropriate cardiac monitoring can be clinically important.

12. Respiratory Involvement

Respiratory muscle weakness can develop as the disease progresses.

This may lead to:

Reduced respiratory reserve.

Sleep-related hypoventilation.

Recurrent respiratory infections.

Respiratory failure in advanced disease.

Respiratory involvement generally occurs later than in classic Duchenne muscular dystrophy.

13. Diagnosis

Diagnosis is primarily based on genetic testing of the DMD gene.

This can identify deletions, duplications, or other pathogenic variants affecting dystrophin production.

Genetic testing has largely reduced the need for muscle biopsy in straightforward cases.

14. Muscle Biopsy

If genetic testing is inconclusive, muscle biopsy may sometimes be useful.

Immunohistochemical or protein analysis can demonstrate dystrophin that is reduced in amount or abnormal in size.

This contrasts with DMD, where dystrophin is usually nearly or completely absent.

15. Management

Management is multidisciplinary and focuses on preserving mobility, preventing complications, and monitoring cardiac and respiratory function.

Care may involve:

Neurology.

Physiotherapy.

Cardiology.

Respiratory medicine.

Rehabilitation.

Genetic counselling.

16. Physiotherapy

Physiotherapy helps maintain:

Joint mobility.

Muscle function.

Posture.

Walking ability.

Stretching and contracture prevention are important as weakness progresses.

Excessive high-intensity exercise that causes muscle injury should generally be avoided.

17. Cardiac Management

Patients require periodic assessment of cardiac function.

This may include:

ECG.

Echocardiography.

Cardiac MRI when indicated.

Cardiomyopathy may be treated with standard heart-failure therapies such as ACE inhibitors or related agents and beta-blockers when appropriate.

18. Genetic Counselling

Because BMD is X-linked, genetic counselling is important for affected families.

Carrier testing can help identify female relatives who may have reproductive implications or require cardiac surveillance.

Prenatal or reproductive genetic options may also be discussed when appropriate.

19. Becker versus Duchenne – Note Form

Inheritance in both: X-linked recessive.

Gene in both: DMD gene.

Protein in both: dystrophin.

Duchenne: dystrophin essentially absent.

Becker: dystrophin reduced or structurally abnormal but partly functional.

Duchenne onset: early childhood.

Becker onset: later childhood, adolescence, or adulthood.

Duchenne course: more severe and rapidly progressive.

Becker course: milder and more slowly progressive.

Both may show: proximal weakness, Gowers sign, calf pseudohypertrophy, elevated CK and cardiomyopathy.

Key Clinical Pattern

Remember Becker muscular dystrophy as:

X-linked dystrophin disorder + later onset + milder progression than Duchenne.

The easiest distinction is:

Duchenne → little or no functional dystrophin.

Becker → some functional dystrophin remains.

Therefore:

More dystrophin → later presentation and milder disease.