What is Muscular Dystrophy?
Muscular dystrophy (MD) is a collective term that refers to a group of more than 30 diseases. The common characteristic of all the conditions is that they cause muscle weakness and a progressive loss of muscle tissue. There is no known cure for any of the diseases.
Some of the differences between the different types of MD lie in the muscles affected and the stage of life at which their symptoms first appear.
Duchenne Muscular Dystrophy
Duchenne muscular dystrophy (DMD) is the most common type of muscular dystrophy. It almost exclusively affects boys, but girls may develop a milder form of the disease. Symptoms usually appear first in early childhood (generally at age 2 or 3) and get progressively worse.
Symptoms of DMD include:
- Difficulty walking, running, or jumping
- Awkward gait (waddling or toe-walking)
- Trouble moving from a lying or sitting position
- Muscle stiffness or pain
- Unusually large calf muscles
- Learning disabilities
Becker Muscular Dystrophy
Symptoms of Becker MD are similar to those of DMD but may be milder. Becker MD’s signs usually first appear later than those of DMD, with onset occurring in the patient’s teens or 20s.
Myotonic Muscular Dystrophy (Steinert’s Disease)
This form of the disease is characterized by muscles that fail to relax after they contract. Muscles of the face and neck are usually the first to be affected, and the symptoms typically first appear in adulthood.
Congenital Muscular Dystrophy
These forms of the disease have symptoms that are apparent at birth or during infancy. The severity of the symptoms and the speed at which they progress vary.
What Causes 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 abnormal production of a particular protein.
In the case of Duchenne muscular dystrophy, the affected protein is called dystrophin. In the 1980s, scientists discovered the protein and the gene abnormality that affects it. When the genetic mutation interferes with dystrophin production, the lack of the protein causes muscle cells to be especially susceptible to damage.
Is Muscular Dystrophy Hereditary?
Most types of muscular dystrophy run in families, and the genetic trigger for the disease is passed from parent to child. Sometimes, though, the genetic abnormality that causes the condition isn’t present at birth and occurs sometime later in life. This makes it possible for someone who doesn’t have a family history of MD to develop the disease.
Duchenne muscular dystrophy is called an X-linked inherited disorder because the gene responsible for the disease 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; therefore, the DMD 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 that they will develop the disease. However, boys who inherit the DMD mutation don’t have a healthy X chromosome to counteract the mutation and are more likely to develop DMD.
How is Muscular Dystrophy Detected?
The first DMD symptoms often begin to appear around age 2 or 3, but some signs may be present earlier. However, the earliest signs may be difficult to spot, and the average age of diagnosis of DMD is 4.
Be alert for the developmental warning signs of DMD in your child. Signs include:
- Difficulty standing from a sitting or lying position
- Delayed walking (later than 15 months)
- Weakness or stiffness in the neck
- Walking with a waddling, toe-walking, or legs-apart gait
- Difficulty running or jumping
- Speech delays
In other types of MD, symptoms may surface later. Causes for concern include progressive muscle weakness, frequent falls, or muscle stiffness.
How is 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.
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. A CK level when there is no apparent muscle injury can show 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 different types of MD.
PLEASE CONSULT A PHYSICIAN FOR MORE INFORMATION.
How is Muscular Dystrophy Treated?
There is no cure for muscular dystrophy, but treatments may slow the progression of symptoms. With treatment, symptoms can often be managed to keep the patient mobile as long as possible and help prevent severe, life-threatening complications.
Medications are typically used to slow the progression of MD and to treat potential complications. Drugs commonly used include:
- Corticosteroids. The steroid prednisone may be able to keep muscles stronger and slow the progressive degeneration of muscle tissue. However, regular use of steroids carries the risk of side effects such as weight gain and brittle bones.
- Immunosuppressants. Medications that limit the action of the body’s immune system may also help to delay muscle degeneration.
- Eteplirsen (Exondys 51) is a new drug that may improve muscle weakness in some DMD cases by targeting specific gene mutations. The drug has been approved as a DMD treatment by the FDA, but evaluation of its effectiveness and safety is ongoing.
Therapy programs directed at specific problems associated with MD may slow down the disease’s progression and delay the worst of the complications.
Commonly used therapies include:
- Physical therapy
- Respiratory therapy
- Speech therapy
- Occupational therapy
Sometimes surgery may be required to address problems, such as abnormal skeletal development caused by MD. Myotonic MD can affect the heart, and a pacemaker may be necessary to keep the heart functioning properly.
How Does Muscular Dystrophy Progress?
Some cases of MD progress slowly, and symptoms may be relatively mild. In severe cases, though, progressive muscle degeneration can lead to complications that are debilitating or life-threatening.
Potential complications of MD include:
- Limited mobility. Muscle weakness can make it hard to get around, and some people with MD eventually lose the ability to walk altogether.
- 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. Some patients may require the assistance of a mechanical ventilator.
- Swallowing problems. Muscles that control the swallowing reflex can be affected. When this happens, maintaining proper nutrition may be difficult, and sometimes a feeding tube is necessary.
- Heart problems. The muscular function of the heart may be impacted by MD, too.
How is Muscular Dystrophy Prevented?
There is no known way to prevent muscular dystrophy in someone born with a genetic mutation responsible for the disease. The cause of spontaneous disease-producing mutations after birth is also unknown, so there’s no way to prevent those cases from happening, either.
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, including educational resources, guides, and links to caregiver networks and support groups.
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. This suggests that MD, at least sometimes, affects the brain, too. Researchers are trying to understand how abnormalities in protein production that weaken muscles might harm brain development or function.
- The genetic mutation that causes myotonic MD produces a toxic chemical that damages muscle tissue. But symptoms of myotonic MD also often include memory, cognitive, and behavioral problems, leading scientists to suspect that the toxic chemical might also damage the brain. Studies have shown that the chemical is present in myotonic MD patients’ brains, and animal studies have shown that the chemical could produce neurological symptoms.
- 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). Dystrophin, the protein impacted by DMD, is also present in the brain, but scientists are not sure what it does. 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.
These research areas could be the first steps in understanding MD’s neurological impact, and a broader understanding could lead to more effective treatments.
Muscular Dystrophy Research
Title: Sleep Intervention in Young Boys With Duchenne Muscular Dystrophy (DMD)
Principal investigator: Roxanna M. Bendixen, PhD
University of Pittsburgh
This project will systematically plan and evaluate the Transdiagnostic Sleep and Circadian Intervention implementation for youth (TranS-CY). As an early-stage study, investigators will focus on recruitment strategies to reach the target population and collection of preliminary data on primary and secondary effects of the TranS-CY. Weekly remote (video web conferencing) parent training sessions will allow investigators to explore adoption through parent adherence and examine whether the essential elements of the TranS-CY intervention (e.g., motivational interviewing, goal setting, problem-solving, sleep routine scheduling, monitoring) can be consistently taught by clinicians and implemented by parents into the home setting.
Title: Limb Girdle Muscular Dystrophy Type 2E Recruitment Study
Principal investigator: Jerry R. Mendell, MD
Nationwide Children’s Hospital
This is a longitudinal observational study. It is a 24-month study with the possibility of extending the data time points. Visits will occur monthly. However, at the discretion of the PI, subjects may not be required to return monthly. These subjects may return at intervals ranging from 2 months to a max of 6 months apart.
If the subjects fall out of the inclusion criteria or not be eligible for the LGMD2E gene therapy trial, they will be given the opportunity to roll over into the Natural History for LGMD (IRB17-01086). If a subject is invited to screen for the gene therapy trial, they will discontinue this trial. By being in this study, it is not a guarantee that subjects will be invited to screen for the LGMD2E gene therapy trial.
Title: Validating Cardiac MRI Biomarkers and Genotype-Phenotype Correlations for DMD
Principal investigator: Daniel Ennis, PhD
University of California, Los Angeles
Los Angeles, CA
This study will collect MRIs from healthy volunteer boys and boys with Duchenne Muscular Dystrophy (DMD) to help researchers identify and validate cardiac MRI biomarkers to better understand the heart’s health and changes in heart health over time in boys with DMD.
Currently, there is a lack of sufficiently well characterized cardiac MRI biomarkers that can serve as endpoints for detecting on-target and/or off-target cardiac effects during clinical drug trials for boys with DMD.
Consequently, the first objective is to identify and characterize several cardiac MRI biomarkers for boys with DMD.