Becker Muscular Dystrophy (BMD)
Becker muscular dystrophy, also known as “BMD”, is a form of muscular dystrophy, a genetic disorder that gradually makes the body's muscles weaker and smaller. BMD is similar to Duchenne muscular dystrophy “DMD”, but it is a less severe form and allows better voluntary muscle control except the heart muscle is also affected with dilated cardiomyopathy, typically begins in adolescence. Both BMD and DMD occurs primarily in boys, but BMD is less frequent in which the birth prevalence is 1 in 30,000 newborn males.
Symptoms
The symptoms of BMD are similar to DMD but start later and are milder with slower yet less predictable course.
BMD often has a range of onset age, from late childhood to adolescence or late twenties, with average age of diagnosis is about 11 years old. Initial symptoms include cramping during exercise and diminished stamina while doing physical activities. Muscle loss usually begins in the proximal muscles, most often from the hip, pelvic area, thighs and shoulders, and patients are noticed to often have enlarged calf muscles. To compensate for muscle deterioration, patients often walk on toes with their stomach forward or walk with a waddling gait. Over time, patients gradually lose their balance and coordination with signs of frequent falls. There is also a shortening of muscle fibers which lead to the inability to move certain muscles (contractures).
However, dissimilar to DMD, BMD patients can walk independently, and this ability is usually lost from between the ages of 40-60, although this could sometimes happen earlier. Breathing muscles tend to stay strong enough that a ventilator or other mechanical breathing help isn't needed although at times some patients may feel breathless and fatigued.
In later life, patient often have significant heart involvement such as dilated cardiomyopathy, the most common cause of death in individuals with BMD, which enlarges and weakens the heart muscle, preventing it from pumping blood efficiently.
Some patients are also noted to have cognitive problems which include attention focusing, verbal learning and memory, and emotional interaction.
Cause
Similar to DMD, BMD is caused due to a specific mutation of the dystrophin gene on the X chromosome. Instead of producing the protein dystrophin which helps protect muscle fibers and play a role in chemical signaling within cells, it produces a protein called dystrophia that causes muscle fibers to gradually weaken and wear away. However, it is different from DMD in the sense that while there is no functional dystrophin produced in DMD, some is produced in BMD, thus its symptoms are milder.
Carrier
Carriers are females who have a normal dystrophin gene on one X chromosome and an abnormal dystrophin on the other X chromosome. Most carriers appear normal, but a minority (about 10 percent) can exhibit symptoms associated to BMD, namely skeletal and cardiovascular complications.
BMD affects primarily on boys because the dystrophin gene is on the X chromosome. Males have only one X chromosome whereas females have two. Therefore, a female carrier will not develop the disease as the normal gene on one X chromosome compensates for the gene defect on the other X chromosome. A BMD mother has a 50% chance passing the genetic mutation on to her children - any son who receives the defective gene will have the disease as male only has one copy of the dystrophin gene while any daughter who receives the defective gene will become a carrier herself, the same way as her mother carrier.
Life expectancy
As the severity and conditions vary greatly amongst BMD patients, it is difficult to determine the life expectancy outlook for each individual. Over 90% of BMD patients live over 20 years of age while most patients will live between 40-50 years of age and about half pass away due to cardiac failure from cardiomyopathy (enlargement of the heart). However, in some cases with proper medical intervention and close monitoring a normal or nearly normal life can be expected.
Treatment
Although there is no cure for BMD at the moment, but there are certain therapies and medicines to help alleviate symptoms and control related complications, providing an improved quality of life.
Since the diseases can vary greatly in its severity, the uses and emphasis of non-pharmacologic and pharmacologic treatment options will vary according to the outlook of your BMD child.
- Non-pharmacologic treatments
In general, it is recommended that your child to remain active and do frequent exercise, since inactivity can worsen the deterioration. It is important to consult with your doctor first, since too much physical activity as well as certain postures/exercises can make muscle damage worse.
Therapy options should include physical therapy and active and passive exercise to build muscle strength and prevent contractures. Surgery may be recommended in some patients to treat contractures or scoliosis. Braces may be used to prevent the development of contractures. The use of mechanical aids (e.g., canes, braces, and wheelchairs) may become necessary to aid walking (ambulation). Please visit “Intervention” page on this website for the different therapies.
- Pharmacologic treatments
In terms of pharmacologic treatment, data for and against the use of corticosteroids in BMD is lacking. As long-term use of corticosteroids result in significant side effects, such as weight gain, decreased bone density, behavioral abnormalities, cataracts and growth retardation, prescription to your child will only be considered if his course is severe.
A nutrition guide to manage the side effects of corticosteroids can be found here.
The use of other drug treatments (e.g. muscle relaxants, anti-inflammatory medications) to alleviate muscle paint must also take into consideration their interactions with other medications and associated side effects, especially those that might affect cardiac or respiration function.
Heart medications, such as angiotensin-converting enzyme (ACE) inhibitors or beta blockers, may be used if muscular dystrophy damages the heart.
- Potential treatments under research and testing
Related R&D is primarily focused on DMD. These potential treatments, if proved effective, is expected to benefit BMD patients.