Becker Muscular Dystrophy

What Causes Becker Muscular Dystrophy?

Muscular dystrophy occurs when the body cannot produce the kinds of proteins needed to build and protect muscle cells. Genes control the production of these proteins, and each type of MD is characterized by a gene abnormality that causes the abnormal production of a particular protein.

In the case of Becker muscular dystrophy, the affected protein is called dystrophin. An abnormal change (mutation) in the DMD gene interferes with the production of dystrophin; the lack of the protein causes muscle cells to be especially susceptible to damage.

Problems with dystrophin are also the cause of Duchenne muscular dystrophy. In DMD, gene mutations cause an almost total absence of dystrophin. In contrast, the mutations associated with BMD produce an altered form of dystrophin that doesn’t function as well as it should. This difference likely explains BMD’s milder symptoms compared to those of DMD.

Is Becker Muscular Dystrophy Hereditary?

Most types of muscular dystrophy run in families, and the genetic trigger for the disease is passed from parent to child. Becker muscular dystrophy is an X-linked inherited disorder because the gene responsible for the condition lies on the X chromosome. Women’s cells contain two X chromosomes, and men’s cells have one X and one Y chromosome.

Everyone inherits one X chromosome from their mother and either an X or Y chromosome from their father, so the BMD genetic mutation could be inherited from either parent. But because girls have two X chromosomes, they probably have inherited at least one healthy X chromosome, making it unlikely to develop the disease. However, girls with the mutation sometimes develop mild muscle weakness and heart problems. In addition, boys who inherit the BMD mutation don’t have a healthy X chromosome to counteract the mutation and are more likely to develop BMD.

How Is Becker Muscular Dystrophy Detected?

The earliest symptoms of BMD typically begin between adolescence and early adulthood. Early signs of BMD may include:

• Muscle weakness, especially in the legs and pelvis
• Frequent falls
• Muscle stiffness
• Change in walking gait
• Difficulty with physical activities or sports

In some cases, heart problems are the first sign of BMD. Symptoms of cardiomyopathy can include:

• Irregular heartbeat
• Shortness of breath
• Fatigue
• Swelling in the legs and feet

How Is Becker Muscular Dystrophy Diagnosed?

If a doctor is presented with symptoms that look like those of muscular dystrophy, they will begin the diagnostic process by conducting a physical exam and gathering a medical history. If it appears that a muscle disease is likely, several different tests can help determine if there is a muscle problem and which disease is the cause. Diagnosis of BMD can be challenging because its symptoms closely resemble those of DMD and other muscular disorders.

Possible diagnostic tests include:

• Creatine kinase (CK) test. Creatine kinase (CK) is a type of protein called an enzyme. CK in the blood is normal, but higher enzyme levels are created when muscles are damaged. Therefore, an elevated CK level when there is no apparent muscle injury can show the presence of a muscle disease like MD.
• Electromyography. This test uses an electricity-sensing needle probe to measure muscle function. The test can detect muscle abnormalities that could be a sign of MD.
• Muscle biopsy. This test involves removing and examining a small amount of muscle tissue. A biopsy may be able to detect muscle abnormalities caused by MD.
• Genetic testing. These blood tests look for the specific genetic abnormalities that are responsible for BMD.

PLEASE CONSULT A PHYSICIAN FOR MORE INFORMATION.

How Is Becker Muscular Dystrophy Treated?

There is no cure for muscular dystrophy, but with treatment, symptoms can often be managed to keep the patient mobile as long as possible and help prevent severe, life-threatening complications. Therapy programs directed at specific problems associated with BMD may delay or prevent the worst of the complications.

Commonly used therapies include:

• Physical therapy
• Respiratory therapy
• Speech therapy
• Occupational therapy

Regular monitoring of the patient’s heart health is necessary to watch for the development of cardiomyopathy.

How Does Becker Muscular Dystrophy Progress?

BMD often progresses slowly, and symptoms may be relatively mild. In severe cases, however, progressive muscle degeneration can lead to debilitating or even fatal complications. Cardiomyopathy and respiratory problems may eventually be life-threatening, but with proper management of these conditions, most people with BMD survive well into adulthood.

Potential complications of BMD include:

• Limited mobility. Muscle weakness can make it hard to get around, and some people with BMD eventually lose the ability to walk altogether and need a wheelchair.
• Skeletal problems. The spine, in particular, is vulnerable to abnormal development when weak muscles are unable to support it.
• Respiratory problems. The muscles responsible for controlling breathing can be affected by MD, making it difficult for patients to breathe easily on their own.
• Heart problems. Cardiomyopathy sometimes develops rapidly and can cause life-threatening complications.

How Is Becker Muscular Dystrophy Prevented?

There is no known way to prevent the onset of Becker muscular dystrophy in someone born with a genetic mutation responsible for the disease. Therefore, people who have a family history of the disease should seek the advice of a genetic counselor to assess their risk if they plan to have children.

Becker Muscular Dystrophy Caregiver Tips

Studies have shown that caring for someone with muscular dystrophy can significantly negatively impact the caregiver’s life. Caregivers are at risk for depression, sleep problems, stress, anxiety, relationship problems, and low self-esteem. Caregivers are also likely to have difficulty performing well at work, and many caregivers quit working entirely to care for their loved one.

Because of these risks, caregivers must take advantage of support systems to keep themselves healthy. The Muscular Dystrophy Association maintains a collection of resources for caregivers that includes educational resources, guides, and links to caregiver networks and support groups.

Many people with MD also suffer from other brain-related issues, a condition called co-morbidity. Here are a few of the disorders commonly associated with MD:

• People with MD are more likely to suffer from depression.
• People with MD are at increased risk of anxiety disorders such as generalized anxiety disorder.
• Obsessive-compulsive disorder (OCD) risk is higher in people with MD.

Becker Muscular Dystrophy Brain Science

The most apparent effects of muscular dystrophy occur in the muscles, but it’s not uncommon for MD sufferers to have cognitive or mental health problems, too. This suggests that MD, at least sometimes, affects the brain, too. Researchers are trying to understand how abnormalities in protein production that weakens muscles might also harm brain development or function.

People with Duchenne MD (DMD) often suffer from cognitive limitations and psychological disorders such as attention-deficit/hyperactivity disorder (ADHD) or obsessive-compulsive disorder (OCD). These symptoms are less common in Becker MD, but a small percentage of people with BMD have cognitive or intellectual disabilities.

Dystrophin, the protein impacted by BMD, is also present in the brain, but scientists are unsure of what it does there. Even though the protein’s role in the brain is still unknown, one study has linked dystrophin deficit with changes in brain development and a higher risk of cognitive problems.

Becker Muscular Dystrophy Research

Title:  A Study to Assess Safety, Tolerability, and PK of EDG-5506 in Healthy Volunteers and Becker Muscular Dystrophy Adults

Stage: Recruiting

Edgewise Therapeutics, Inc.

San Antonio, TX

EDG-5506 is an investigational product intended to protect and improve the function of dystrophic muscle fibers. This Phase 1 study of EDG-5506 will assess the safety, tolerability, and pharmacokinetics (PK) and EDG-5506 in healthy adult volunteers and adults with Becker muscular dystrophy (BMD).

Enrolled participants in this study will receive a single oral dose or multiple oral doses of EDG-5506 or a placebo. Blood and urine samples will be collected to measure how the body processes EDG-5506 and responds when exposed to EDG-5506. Participants in the single ascending dose part of the study will remain in the clinic for seven days with a 42-day follow-up period. Participants in the multiple ascending dose part of the study will remain in the clinic for 16 days with a 13-day follow-up period. Safety, tolerability, and pharmacokinetics of EDG-5506 will be assessed in healthy volunteers before enrolling participants with Becker muscular dystrophy.

Title:  Brain Involvement in Dystrophinopathies Part 2

Stage: Not Yet Recruiting

Contact: Professor Francesco Muntoni

University College London Hospitals

London, UK

This study aims to understand the relationship between DMD and BMD brain comorbidities and the location of the gene mutation that causes the disease.

Intellectual disability and neurobehavioural comorbidities affect at least 50% of individuals with Duchenne muscular dystrophy (DMD). Although a rare genetic disease, DMD is the most common form of muscular dystrophy in childhood. Several studies have documented that 25% of the DMD population has an intellectual disability, with recent studies suggesting that autism and clinically relevant hyperactivity affects 20% and 25% of DMD boys, respectively. A milder allelic variant, named Becker muscular dystrophy (BMD), has a similar prevalence in the population and is also associated with variable degrees of central nervous system (CNS) comorbidities, which have been less well defined.

This knowledge gap will be addressed in a large multicenter study funded by the European Commission (EU H2020) involving six countries (Denmark; The Netherlands; France; Spain; Italy, and the UK) with the most prominent European neuromuscular centers and advocacy groups. The aim will be to study the neurobehavioral aspects of DMD and BMD and their correlation to the genotype.

This study will involve male participants with DMD aged 5-17 years and with BMD aged 5-50 years, who will complete a battery of cognitive and behavioral assessments. This study aims to deep phenotype a cohort of 270 individuals with DMD and BMD, focusing on the cognitive and neurobehavioral aspects of these conditions. A sub-group of patients will also undergo magnetic resonance imaging (MRI) to investigate brain structure, volumetric features, perfusion, functional connectivity, and metabolism. This information will then be correlated to the location of the underlying DMD gene mutation. The brain imaging part is also going to involve age and sex-matched controls.

While there have been significant improvements in defining the genetic basis of the skeletal aspects of dystrophinopathies and their correlation to the DMD genotype, our knowledge on the spectrum of lifespan CNS comorbidities and the precise genotype/phenotype correlations in patients with different DMD mutations is still limited. A study looking into the association between different dystrophin isoforms and different CNS manifestations would therefore offer a unique opportunity to unravel the role of specific dystrophin isoforms and the associated circuitries in brain function.