Muscular Dystrophy

MD refers to a group of more than 30 diseases that cause muscle weakness and loss of muscle mass and tissue.

Different types of MD affect different areas of the body and vary in symptom severity. Some forms of MD appear in infancy or childhood, while others may not appear until middle age or even later. All forms of MD get worse with time, as a person’s muscles get weaker.¹

Because some types of MD are more common than others, statistics about the number of people affected by MD may differ. The Centers for Disease Control and Prevention provides more details about the number of people affected by MD.

NIH research on MD is led by the National Institute of Neurological Disorders and Stroke (NINDS). The NINDS website on MD offers more specific information.

Most cases of MD are caused by gene mutations (changes in the DNA sequence) that affect muscle proteins.

The mutations are usually inherited, but in some cases they occur spontaneously. These spontaneous mutations can then be inherited by an affected person’s offspring.¹

There are three different inheritance patterns for most forms of MD. When a mutation that causes MD is inherited by a parent with the condition, this is known as autosomal dominant inheritance.

In contrast, for most autosomal recessive conditions, the gene mutation must be inherited from both parents. Both matching genes must include a mutation to cause the disease.

However, the inheritance pattern for many types of MD is called “X-linked recessive,” meaning that the genetic change is passed from one generation to the next through the X chromosome.²

Girls and women have two X chromosomes (XX), while boys and men have one X and one Y chromosome (XY). This pattern is the reason certain types of MD, whose mutations are on the X chromosome, are more common in males than in females.

• If a female has one X chromosome with the genetic mutation and one X chromosome without, she may not have symptoms or may have milder MD than males have. She is called a “carrier” because she has the genetic mutation and can pass it on to her children.
• Because males have only one X chromosome, if they have the genetic mutation, they will usually have symptoms of MD or more severe MD symptoms than females do.

Hundreds of genes are involved in making proteins that affect muscles. Each form of MD is caused by a genetic mutation that is unique to that type. For instance:

• Duchenne MD results from a genetic mutation that leads to a lack of dystrophin, a protein that helps strengthen muscle fibers and protect them from injury.¹ It can be inherited in an X-linked recessive manner.
• Myotonic MD is caused by an abnormal expansion of certain DNA sequences on one of two different genes. Most people may have around 40 repeats of a certain DNA code in their gene, but people with myotonic MD have 4,000 or more repeats. These repeats cause errors in the “instructions” for making muscle proteins, meaning the body may not make enough of the protein or may not make usable forms of the protein. In some cases, the instructions themselves build up to high levels; this buildup causes problems with the protein. Myotonic MD can be inherited in an autosomal dominant manner.

MD is not contagious and cannot be caused by injury or activity.¹

There are more than 30 types of MD, each with features that are unique in some way. Brief descriptions of some common (sometimes called “primary”) types of MD and a few of their symptoms are included here.¹

For more detailed information about MD types and symptoms, visit the National Institute of Neurological Disorders and Stroke website, Muscular Dystrophy: Hope Through Research.

The first step in diagnosing MD is a visit with a healthcare provider for a physical exam. He or she will ask a series of questions about the person’s family history, including any family members with MD, and medical history, such as muscle problems the person may be experiencing.

Different tests can help healthcare providers diagnose MD and determine which type of MD is present. The tests also may rule out other problems that could cause muscle weakness, such as injury, toxic exposure, medications, or other muscle diseases. These tests may include:¹

• Blood tests to measure levels of certain substances that may be high in someone with MD. Elevated levels of these substances can signal muscle weakness, injury, and disease and point to a need for additional testing. Some of these may include:
  • Serum creatine kinase, an enzyme released into the bloodstream when muscle fibers are damaged
  • Serum aldolase, an enzyme that helps break down sugars into energy
  • Myoglobin, a protein that carries and stores oxygen in muscles
• Muscle biopsies, which involve the removal of a small piece of muscle tissue using a needle or small incision. Providers examine the tissue under a microscope to check for hallmarks of MD. Patients diagnosed by muscle biopsy usually need genetic testing as well to confirm mutations in their genes.²
• Genetic testing to look for genes known either to cause or be associated with inherited muscle disease. DNA analysis and enzyme assays can confirm the diagnosis of certain neuromuscular diseases, including MD.
• Neurological tests to rule out other nervous system disorders, identify patterns of muscle weakness and wasting, test reflexes and coordination, and detect contractions.
• Heart testing, such as an electrocardiogram (ECG), to measure the rate and frequency of heartbeats, or echocardiogram (Echo), to measure the force of heartbeats and look at the structure of the heart. Some forms of MD cause heart problems such as an irregular heartbeat.³
• Exercise assessments to measure the patient’s muscle strength and breathing and detect any increased rates of certain markers following exercise.
• Imaging tests such as magnetic resonance imaging (MRI) and ultrasound imaging, which use radio waves/magnetic fields and sound waves, respectively, to take pictures of the inside of the body, examine muscle quality and bulk, and measure fatty replacement of muscle tissue.

For more information about diagnosing MD, visit the National Institute of Neurological Disorders and Stroke website Muscular Dystrophy: Hope Through Research.

Currently available treatments for MD can help manage and reduce the severity of symptoms. Ongoing research on treatments, including some gene-based approaches, also show promise for slowing or even reversing some symptoms of certain types of MD.

The information provided here is not all-inclusive of the treatments or medications that might be used or prescribed for people with MD. If you have questions about treatments for MD, please discuss them with your healthcare provider.

NIH research on MD is led by the National Institute of Neurological Disorders and Stroke (NINDS). The NINDS website on MD offers more comprehensive information about treatments.

MD treatments may include the following.^1,2,5

Physical Therapy

Beginning physical therapy early can help keep muscles flexible and strong. A combination of physical activity and stretching exercises may be recommended for people with MD.

Respiratory Therapy

Because the body relies on muscles such as the diaphragm to breathe, weakened muscles from MD may affect breathing. Many people with MD do not realize they have lost respiratory strength until they have difficulty coughing or an infection leads to pneumonia. Shortly after MD is diagnosed, specialists can suggest treatments to prevent or delay respiratory problems. Eventually, some people with MD may need a ventilator to help them breathe.

Speech Therapy

MD patients who experience weakness in the facial and throat muscles may benefit from speech therapy to teach them how to maximize their muscle strength. Some methods include slowing the pace of their speech, pausing more between breaths,³ and using specialized communication equipment.

Occupational Therapy

As physical abilities change, occupational therapy can help patients with MD relearn lost motor skills and learn ways to work around weakened muscles. Occupational therapy also teaches people with MD how to use assistive devices, such as wheelchairs, eating utensils, and personal items, including hair- and toothbrushes.

Surgery

At various times and depending on the form of MD, many people with MD need surgery to treat some of the conditions associated with MD. For instance, people with myotonic MD may need to have a pacemaker installed to treat heart problems or surgery to remove cataracts, a clouding of the lens of the eye that blocks light from entering the eye. Some people with MD may need surgery for scoliosis, or curvature of the spine.

Drug Therapy

Certain medications can help delay damage to muscles or minimize the symptoms of MD. These can include the following:

• Glucocorticoids^4,5 such as prednisone or deflazacort, which was approved by the U.S. Food and Drug Administration (FDA) for treating DMD in 2017. Studies show that daily treatment with prednisone can increase muscle strength and respiratory function and slow the progression of weakness in MD.
  • A new glucocorticoid treatment called vamorolone is being studied in boys with DMD. Early results showed the treatment had similar benefits to those from prednisone but without the side effects.⁶
  • NICHD-funded researchers found that vamorolone also helped treat symptoms of limb-girdle MD in animal models. (PMID 30166241)
• Anticonvulsants. Typically taken for epilepsy, these drugs may help control seizures and some muscle spasms in people with MD.
• Immunosuppressants. Commonly given to treat autoimmune diseases such as lupus and eczema, immunosuppressant drugs may help delay some damage to dying muscle cells in MD.
• Beta blockers, angiotensin-converting-enzyme (ACE) inhibitors, and other medications for treating heart problems, such as high blood pressure and heart failure, which are associated with certain types of MD.

Gene-Based Therapy

Restoring a gene’s ability to produce usable proteins as a treatment for MD is an active area of study, but many of these therapies are still in development. Some methods focus on correcting the function of a specific gene, while others rely on a genome-wide approach.⁷

Other gene-based methods, such as the drug eteplirsen, uses a process called “exon skipping” to produce usable dystrophin protein by “skipping” over the part of the gene that causes problems with the muscle proteins. In exon skipping, more muscle protein is available and usable, even though it is shorter than the normal protein. FDA approved eteplirsen for treatment of DMD in 2016,⁸ golodirsen in 2019,⁹ and viltolarsen in 2020.¹⁰ These treatments require weekly intravenous injection and do not cure DMD. Studies are ongoing for all three of these drugs to demonstrate clinical benefit beyond increased dystrophin production. Because the gene that causes DMD is very large, less than one-quarter of people with DMD may respond to these treatments. Research is also ongoing on other drugs that increase production of dystrophin in fetuses and correct other problems with protein instructions and production.