Becker Muscular Dystrophy

What is Becker muscular dystrophy?

Summary

Becker muscular dystrophy (BMD) is a genetic condition that leads to progressive muscle wasting due to a mutation in the gene that makes a muscle-supporting protein called dystrophin.

BMD typically presents as a less severe form of muscle wasting than the similar Duchenne's muscular dystrophy (DMD) because people with BMD have reduced dystrophin, whereas people with DMD have a complete absence of functional dystrophin. BMD presents later in life than people with DMD, but both conditions can become debilitating and lead to early death. BMD is found in about three to six out of every 100,000 births and is much more common in males than females.

Symptoms include difficulty moving and standing up, extra-large calf muscles, heart trouble, and sometimes cognitive or behavioral issues.

The diagnosis is confirmed by genetic testing or, rarely, testing a piece of muscle tissue. Treatment mainly involves steroid medications.

Recommended care

You should visit your primary care physician to confirm the diagnosis and discuss treatment options for managing symptoms.

Becker muscular dystrophy symptoms

Some symptoms of BMD can be observed; others are discovered through testing.

Observable symptoms

The main, observable symptoms of BMD are detailed below.

• Difficulty with movement: The pattern of muscle weakness classically seen with BMD is one in which the muscles of the thighs and hips are affected before the muscles of the lower legs, and the legs are affected before the arms. This can lead to difficulty with running, walking up steps, or jumping. Unlike in DMD, in which children start to show difficulty with walking as very young children, most children with BMD remain ambulatory until about age 16.
• Difficulty getting up from a seated position: As described above, the muscles of the hips are usually the first to be affected in BMD. This leads to Gower's sign, which is one of the earliest clinical indicators that a child may be affected by DMD or BMD. The Gower's sign is a maneuver that children with DMD or BMD naturally develop to assist themselves in standing up. Because their lower limbs are weak, they predominantly use their arms to hoist themselves from a seated position. This usually entails using upper body strength to push themselves up from the ground and then continue to pull their upper bodies by pushing downwards against their lower limbs.
• Calf pseudohypertrophy: People with BMD may appear to have very large or muscular calves. "Pseudohypertrophy" indicates that the calves appear deceivingly muscular. Rather than excess of muscle tissue in the calves, there is an abundance of scar tissue from the breakdown of muscle that does not properly function thus creating this overly large appearance.

Symptoms discovered through testing

Symptoms of BMD that are discovered through testing include the following.

• Cardiomyopathy: This is a condition in which weakness in the heart muscle makes it difficult for the heart to pump the necessary amount of blood to the rest of the body. The blood ends up pooling in the chambers of the part, eventually leading to dilation of the chambers a condition called dilated cardiomyopathy. Cardiomyopathy is often the presenting feature in BMD patients, since the muscle weakness of the limbs may not appear until adolescence or young adulthood.
• Shortness of breath: People with BMD may experience shortness of breath, either at rest or with activity, for several reasons. As discussed above, BMD can affect the muscles of the heart. If the heart is not pumping properly, it cannot send blood to the lungs to pick up oxygen and deliver this oxygen to the rest of the body. This would lead to easy fatigue with even minimal activity. Alternatively, shortness of breath can be caused by wasting of the muscles of the diaphragm a muscle in the abdomen that moves air in and out of the lungs. In advanced cases of BMD, the diaphragm may be affected and function improperly.
• Irregular heart beat: People with BMD whose heart muscles are affected by the condition may begin to experience a feeling of "fluttering" in their chests as the result of an abnormal heartbeat. The poorly functioning heart muscle may start to break down, which leads to scarring of the tissue within the heart. The electrical signals that naturally move through the heart that allows it to beat at a regular rate do not move as well through scarred tissue. As a result, an irregular heartbeat can be felt.
• Cognitive or behavioral disorders: Most people with BMD will be cognitively and behaviorally normal. However, a small number of BMD patients have an impaired IQ, ADHD, and/or anxiety. Research suggests dystrophin plays a role in cognitive development, so a lacking dystrophin protein has learning and behavioral effects.

Becker muscular dystrophy causes

BMD is caused by a mutation in the gene that makes a protein called dystrophin, which normally provides support and stability to muscles as they contract and relax, preventing them from breaking down. The dystrophin protein is found in muscles in the limbs and the heart, which is why these are the two areas of the body most commonly affected by BMD.

The dystrophin gene is located on the X chromosome, which is one of the sex chromosomes. A pairing of X and Y sex chromosomes produces a male and two X chromosomes produces a female. BMD is classified as an X-linked recessive condition. Since dystrophin is on the X chromosome and males only have one X chromosome, their dystrophin is much more likely to be impaired if mutated than females, who have another X chromosome with likely normal dystrophin. If females inherit one copy of the mutated gene but have a normal other X chromosome, they are considered "carriers" of the condition and generally do not manifest BMD symptoms.

Treatment options and prevention

Steroids are the mainstay of therapy for people with BMD. Treatment with either prednisone or deflazacorthas been shown to improve heart and lung health, limb strength, and overall survival in people with DMD. BMD is treated the same way, but studies on the impact of steroids are much more limited in the BMD patient population.

When to seek further consultation

If you have already been diagnosed with BMD

If you have already been diagnosed with BMD and are experiencing irregular heartbeats, shortness of breath, or easy fatigue, you should seek care from your physician right away.

If you or your child are demonstrating symptoms

If you or your child are demonstrating persistent muscle weakness, especially when attempting to stand, you should go see your physician.