Becker muscular dystrophy (BMD) is a neuromuscular disease characterized by progressive muscle wasting and weakness due to degeneration of skeletal, smooth and cardiac muscle. This form of muscular dystrophy is named after the German doctor Peter Emil Becker who described the condition in 1955. Becker muscular dystrophy follows x-linked recessive inheritance so it mostly affects males, but some females are affected. The clinical picture is similar to that of Duchenne muscular dystrophy (DMD). BMD is generally milder than DMD, and the onset of symptoms usually occurs later – teens or early twenties and symptoms vary greatly between affected individuals.
BMD is caused by a defect in the dystrophin gene located on the X-chromosome. The faulty gene results in a deficiency of the protein dystrophin, causing muscles to deteriorate and break down in males. While females have two copies of the X-chromosome, a defect in one can nearly always produce enough dystrophin to have normal muscle function making her a carrier. Males, however, have only one X-chromosome and therefore one dystrophin gene copy. So, a faulty dystrophin gene results in DMD or BMD.
The incidence and prevalence of BMD are lower than those of DMD. The estimated incidence of BMD is 1 individual per 30,000 male births, compared with 1 individual per 3500 male births for DMD. The prevalence of BMD is 17-27 cases per 1 million population.
Symptoms include muscle weakness of the lower body, including the legs and pelvis area, slowly gets worse, causing:
- Difficulty walking that gets worse over time; by age 25 to 30, the person is usually unable to walk
- Frequent falls
- Difficulty getting up from the floor and climbing stairs
- Difficulty with running, hopping and jumping
- Loss of muscle mass
- Toe walking
- Muscle weakness in the arms, neck and other areas is not as severe as in the lower body
Other symptoms may include:
- Breathing problems
- Cognitive problems (these do not get worse over time)
- Loss of balance and coordination
Muscles lose their elasticity, leading to tightness (contractures) around joints, and difficulty with stretching leg and heel muscles. Contractures can lead to skeletal deformities such as scoliosis or a curved spine. Due to the weakening of the heart muscle, people with BMD have a high risk of developing heart disease (cardiomyopathy). Many patients die, due to complications, in their mid-to-late 20s. Less than half of those with Becker MD survive to 40 years of age. Those that do are typically severely disabled.
Once BMD is suspected, diagnostic tests will be offered to establish a definite diagnosis. These may include:
- CPK (CK) Testing: A positive blood test for BMD will demonstrate higher than normal levels of the muscle protein creatine phosphokinase. This enzyme leaks out of damaged muscles, and into the blood serum. This is not, however, a conclusive test, as an elevated amount of CPK is also a feature of other muscular dystrophies.
- DNA Studies: DNA studies are able to give definitive information about the genetic abnormality responsible for the faulty BMD gene, whilst in others, the abnormality is not able to be exactly defined.
- Muscle Biopsy: The test is positive for BMD if there is an abnormally low level of dystrophin present.
- Electromyography: EMG gives information on the electrical activity of the muscle tested. It tells whether the muscle weakness is caused by damage to the muscles, as in BMD, or damage to the nerves, as in other muscular dystrophy conditions such as Friedrich’s Ataxia.
- Genetic Counselling
No specific treatment is available for Becker muscular dystrophy but the quality of life and lifespan can be improved with appropriate care. Physical and occupational therapy can reduce or delay joint contractures. Surgery is sometimes recommended to treat contractures or scoliosis. Weight control can help to reduce stress on the heart and muscles. Corticosteroids are often prescribed to help slow down the loss of muscle function. Routine monitoring by a cardiologist is recommended.
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