Becker Muscular Dystrophy (BMD)

BECKER MUSCULAR DYSTROPHY

Becker Muscular dystrophy is an inherited disorder that is more frequent among males and is characterized by progressive muscle weakness and atrophy or wasting.  It is similar to Duchenne muscle dystrophy but symptoms are milder in form, appear later in childhood or adolescents, and progress at a slower rate. 

Genetics

Becker muscle dystrophy is inherited in an X-linked recessive manner.  In majority of the cases, the condition is passed on by a mother who carries an altered copy of the DMD gene to her son.  In these cases, the mother is the carrier and does not present with signs and symptoms of the disorder.  However, some may have mild muscle weakness and cramps and are at an increased risk of developing heart disease such as dilated cardiomyopathies. 

The gene involved is the DMD gene, which is responsible in producing a protein called dystrophin.  Dystrophin contributes in the stabilization of the cell membrane and in minimizing the injury related to the stress of muscle movement.  Mutations in this gene modify the structure and therefore the function of dystrophin, leading to cell damage, especially of the skeletal and heart muscles.  

Signs and Symptoms

The symptoms usually appear from 2 to 21 years old.  Early in the disease, there may be delay in walking and running, difficulty in getting up from the sitting/ lying position, and frequent falling.  There is also proximal muscle weakness in the arms, neck, and areas but is not as severe as in the lower body.  As the disease progresses, loss of muscle mass is often observed. 

Becker muscular dystrophy is also associated with a heart disease called dilated cardiomyopathy, which is characterized by heart enlargement leading to a weakening of the heart muscles and therefore an ineffective pumping action of the heart.  Symptoms usually appear during early and middle adulthood.

Diagnosis

Aside from a thorough medical history and physical examination, diagnosis can be made through an elevated serum creatine kinase.  The second step is genetic testing to check for a mutation in the dystrophin gene.  If the first two tests are negative or have equivocal results, muscle biopsy is performed to confirm the diagnosis.  Muscle biopsy with dystrophin antibody staining shows the presence of dystrophin in variable percentages.

Other tests that may be done include an Electromyography (EMG), Spinal radiographs, Electrocardiogram (ECG), and Pulmonary function testing.

Treatment

There is currently no known cure or effective treatment for Becker muscular dystrophy.  Management is aimed at controlling the symptoms and in the improvement of the patient’s quality of life. 

Physical and occupational therapy deal with the patient’s functional needs and the activities of daily living.  Speech therapy is beneficial to those with advanced disease because of the possible development of difficulty in swallowing or dysphagia, which puts the patient at risk for aspiration pneumonia.  Surgical treatment may be indicated in those patients with progressive scoliosis and contractures. 

Genetic testing is recommended, especially for women who are daughters of a man who has been diagnosed with the condition because they may be carriers and could pass the condition to their sons. 

References:

http://ghr.nlm.nih.gov/condition/duchenne-and-becker-muscular-dystrophy

http://www.mdausa.org/disease/bmd.html

http://www.umm.edu/ency/article/000706.htm

http://emedicine.medscape.com/article/313417-overview

Tselikas L, et al. Rev Med Interne 2010 Nov 29.

Helderman-van Enden A, et al. Clin Genet 2010 Oct 23.

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