Becker Muscular Dystrophy
Becker muscular dystrophy (BMD) is an X-linked recessive inherited disorder characterised by slowly progressing muscle weakness, particularly affecting the legs and pelvis. It is a type of dystrophinopathy caused by mutations in the dystrophin (DMD) gene. This condition is related to Duchenne muscular dystrophy (DMD), but Becker muscular dystrophy is typically milder due to in-frame deletions in the gene.
Signs and Symptoms
Individuals with BMD typically experience progressive muscle weakness, beginning in the legs and pelvis and eventually affecting the arms, neck, and other areas. Common symptoms include severe upper extremity muscle weakness, toe-walking, difficulty breathing, and the use of Gower's manoeuvre to rise from the floor. Skeletal deformities such as scoliosis and pseudohypertrophy of the calf muscles are also observed. Other symptoms include muscle cramps, heart muscle problems, and elevated creatine kinase levels in the blood.
Complications
Complications associated with BMD include cardiac arrhythmias, mental impairment (less common than in DMD), pulmonary failure, and pneumonia.
Genetics
The DMD gene, located on the X chromosome, is responsible for BMD. It is inherited in an X-linked recessive pattern. Women, having two X chromosomes, can often compensate for the mutation with a working copy of the gene on the other X chromosome, which is why they rarely develop symptoms. Carrier females have a 50% chance of passing the mutation to their offspring. Men with BMD can pass the mutation to their daughters (who become carriers), but not to their sons.
Diagnosis
Diagnosis of BMD involves several tests and exams. A physical exam reveals muscle wasting primarily in the legs and pelvis, with noticeable calf muscle enlargement (pseudohypertrophy). Diagnostic tests include:
- Muscle biopsy: To check for dystrophin in muscle cells.
- Creatine kinase test: Elevated levels of creatine kinase in the blood indicate muscle damage.
- Electromyography: Demonstrates muscle tissue destruction rather than nerve damage.
- Genetic testing: Identifies deletions, duplications, or mutations in the dystrophin gene.
Treatment
There is no known cure for BMD. Treatment aims to control symptoms and improve the quality of life. Regular activity and physical therapy are essential for maintaining muscle strength. Orthopaedic appliances such as braces and wheelchairs may aid in mobility. Immunosuppressant steroids like prednisone can slow disease progression by increasing the production of utrophin, a protein similar to dystrophin.
Cardiac issues associated with BMD may require a pacemaker, ACE inhibitors, or even cardiac transplant. The investigational drug Debio-025, which inhibits cyclophilin D, has shown promise in reducing muscle damage in preclinical studies. Researchers are also looking at the upregulation of compensatory proteins to alleviate symptoms.
Prognosis
The progression of BMD is highly variable. Onset at an earlier age (around 7-8 years) is associated with more severe cardiac involvement, while onset around age 12 shows less cardiac involvement. Despite the symptoms, individuals with BMD can maintain active lifestyles with the help of assistive devices and proper management.
Research
Research efforts are ongoing to find a cure for BMD. Potential treatments include gene therapy (Microdystrophin) and antisense drugs (Ataluren, Eteplirsen). Other medications under investigation include corticosteroids (Deflazacort), calcium channel blockers (Diltiazem), anticonvulsants, and immunosuppressants (Vamorolone). Physical therapy and assisted ventilation remain very important for managing symptoms.
History
Becker muscular dystrophy is named after Dr. Peter Emil Becker, who first described the condition in 1955.
Self-assessment MCQs (single best answer)
What type of inheritance pattern does Becker muscular dystrophy follow?
Which gene mutation is responsible for Becker muscular dystrophy?
What protein is deficient in individuals with Becker muscular dystrophy?
Which of the following symptoms is NOT typically associated with Becker muscular dystrophy?
What type of genetic mutation characterises Becker muscular dystrophy, distinguishing it from Duchenne muscular dystrophy?
What diagnostic test is used to check for dystrophin in muscle cells?
Which medical device may be necessary for individuals with Becker muscular dystrophy due to cardiac complications?
Which investigational drug has shown promise in reducing muscle damage in preclinical studies of BMD?
What is the typical age range for the onset of symptoms in Becker muscular dystrophy?
Who first described Becker muscular dystrophy?
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