Also called: MD
Muscular dystrophy is a group of diseases that cause muscles throughout the body to deteriorate. The diseases, also known as MD, result from genetic mutations. These mutations cause a decrease in the production of proteins that are necessary to build and maintain muscle tissue. Weakness typically begins in the muscles involved in movement and may limit a patient’s mobility. Eventually the weakness progresses to the heart and the muscles of the lungs and may cause these organs to fail.
Researchers have divided MD into 30 diseases classified into nine groups. They are all characterized by muscle weaknesses, but differ in the typical age when symptoms begin and which muscle groups are affected. The disease groups are:
- Duchenne MD
- Myotonic MD
- Facioscapulohumeral MD
- Becker MD
- Congenital MD
- Emery-Dreifuss MD
- Limb-girdle MD
- Distal MD
- Oculopharyngeal MD
The genetic mutations that cause MD are usually inherited. A parent with a family history of the disease may have up to a 50 percent chance of passing it to a child. Some mutations that cause MD are found on the genetic material (chromosomes) that determine gender. This means that those forms of MD may occur only in males, or may be more prevalent or severe in males.
A diagnosis of MD is often based on the onset of signs and symptoms in addition to a family history of the disease. Other tests may be necessary to confirm this diagnosis and eliminate other potential causes of muscular weakness. These might include blood tests, urine tests, tissue biopsies and imaging tests (e.g., MRI scans) of the affected muscles.
Upon diagnosis, supportive treatment may begin to reduce the patient’s symptoms and delay muscle degeneration. At present, there is no cure. Treatment often consists of medication, physical and speech therapy and use of orthopedic devices.
About muscular dystrophy
Muscular dystrophy, or MD, is a collection of genetic diseases that cause muscles to degrade. It can affect both males and females and is generally passed down from parent to child. Although there are many different types of MD, most are characterized by muscle weakness, progressive crippling, loss of mobility and, eventually, death.
Muscles are composed of thousands of muscle fibers that contract as a response to signals from nerves. This results in movement of a body part. As the signals fade, the fibers relax and the body part returns to its resting position.
The relaxation-contraction process of muscles is complex and requires large amounts of energy and proteins to avoid damaging the muscles. Dystrophin and glycoprotein are proteins that help protect the muscles by maintaining a membrane that surrounds each muscle fiber. The absence of these proteins, which occurs in some types of MD, causes the fiber membrane to become damaged and eventually results in the degeneration of the muscles. In general, the muscles are replaced by fatty and connective tissues.
At first, most forms of MD affect the voluntary muscles. These muscles cause movement in the extremities (e.g., arms, legs, fingers, toes) and are controlled by the patient. Eventually, MD progresses from the voluntary muscles to the muscles of the lungs and heart. This limits the patient’s blood circulation and the ability to breathe. Other symptoms related to muscle weakness may be felt throughout the body, including the gastrointestinal system, endocrine glands, spine, eyes and brain. Due to its widespread impact, most forms of MD eventually cause death.
The most common form of the disease, Duchenne MD, is more prevalent in males and rarely affects females. It is estimated that 400 to 600 boys are born with Duchenne MD each year in the United States, according to the U.S. Centers for Disease Control and Prevention.
Types and differences of muscular dystrophy
There are 30 types of muscular dystrophy (MD) that are commonly divided into nine groups. In general, they each cause muscle weakness, lack of coordination, progressive crippling and loss of mobility. They vary in the age of onset, severity, pattern of affected muscles and the gene mutation that causes them.
The four most common groups of MD include:
- Duchenne MD. This is the most common form of the disease and represents approximately half of all cases. According to the National Institutes of Health (NIH), approximately two out of 10,000 people develop this disease. It is also one of the most severe forms of MD. Most patients with Duchenne MD are males. Females may also carry the genetic mutation, although they are less likely to develop the disease and usually have milder symptoms if the disease does occur. Duchenne MD results from a lack of the protein dystrophin, which causes muscle weakness and may lead to scoliosis. This type of MD usually develops between the ages of two and five. Eventually patients become dependent on a wheelchair for mobility. Mortality usually occurs in the late teens or early 20s. Common causes of death include pneumonia, respiratory muscle weakness or cardiac complications.
- Myotonic MD. This is the most common form of adult-onset MD. Male and female patients typically start experiencing symptoms of the disease in their 20s and 30s, though some cases start earlier. The disease typically progresses over many years, causing increasing disability. A childhood form of myotonic MD may begin between the ages of five and 10. There is also a rare form found in fetuses and newborns. All types of myotonic MD are characterized by myotonia, which is a delayed relaxation of muscles following contractions (e.g., difficulty releasing grip, stiff gait). Myotonic MD also affects the central nervous system, heart, adrenal glands, thyroid, eyes, and the gastrointestinal tract. Diabetes, an endocrine system disorder, is also associated with myotonic MD. Myotonic MD may be mild in the first generation that experiences the genetic mutation, but usually becomes more severe when passed to later generations.
- Facioscapulohumeral MD. The third most common form of MD initially weakens the muscles of the face, shoulders and upper arms. It may then progress to other parts of the body. According to the NIH, five out of 100,000 people, both males and females, develop this form of MD. It most often starts while patients are teenagers, but symptom onset is sometimes delayed until they reach their 40s. This disease progresses slowly and patients typically have a normal life expectancy. Later in life, it may lead to severe disabilities.
- Becker MD. This disease is similar to Duchenne MD, though is usually less severe. The NIH estimates between three and six males out of 100,000 have Becker MD. Symptoms typically appear around age 11, though sometimes do not start until age 25. The disease progresses at various speeds, but most patients are still able to walk in their 30s and live into middle age.
The remaining types of MD are rare. They include:
- Congenital MD. Male and female patients may show symptoms of congenital MD at birth or by the age of two. Muscle degeneration can range from mild to severe and most children are unable to sit or stand without support. In many cases, the patient eventually develops scoliosis. Mortality linked to congenital MD is likely to result from lung failure.
- Emery-Dreifuss MD. This disease most often affects males and is usually evident by the time the patient is 10 years old. Some cases do not appear until the patient is in his 20s. Emery-Dreifuss MD may cause arm muscles to contract and elbows can become locked in the bent position. Many patients develop heart conditions by the age of 30 and require a pacemaker. Mortality due to Emery-Dreifuss MD is usually related to lung or heart failure.
- Limb-girdle MD. There are 11 forms of this type of MD that differ in their genetic origin. Each produces a loss of muscle and weakening, mostly in shoulders and hips. Patients typically develop symptoms as teenagers or in early adulthood and it can affect both males and females. Limb-girdle MD progresses at different rates, but most patients are severely disabled within 20 years of disease onset.
- Distal MD. This is one of the less severe types of MD. Initial symptoms are felt in the forearms, hands, lower legs and feet, which are known as the distal (farthest from the hips and shoulders) parts of the body. It progress slowly and can spread to other muscles, including the heart and the muscles around the lungs. Most patients eventually require respiratory assistance from a mechanical ventilator. It affects both men and women and most cases begin between the ages of 40 and 60. There is also a form of distal MD that begins in infants.
- Oculopharyngeal MD. Men and women in their 40s and 50s may experience the first symptoms of this form of the disease. It progresses slowly, but eventually most patients lose their ability to walk. This disease is most common in families of French Canadian descent and Hispanic people of northern New Mexico.
Potential causes of muscular dystrophy
Muscular dystrophy (MD) is generally an inherited condition that results from a mutation in one of several genes that program certain proteins. Proteins are important components of the body’s cells and are essential for the cells to function properly. Genetic mutation can result in abnormal proteins, which can have a wide range of consequences. In some cases, no disease or abnormality results. In others, the impact ranges from minor to severe.
Genetic mutations that affect the proteins involved in building and maintaining muscle can lead to MD. These mutations are often passed from parent to child, but may also occur spontaneously. Children who have a spontaneous mutation in their genes may, in turn, pass the mutation to future generations.
There are several ways in which the genetic mutations that cause MD can be passed from parent to child. Some types of MD (e.g., Emery-Dreifuss MD) can be inherited in more than one way.
Some forms of MD are autosomal dominant, which means that only one parent must carry the gene mutation for the disease to be passed to a child. In the case of autosomal dominant forms of MD, if one parent has the gene mutation, there is a 50 percent likelihood that the mutation will be passed to a child. Forms of MD that are inherited in this way include:
- Distal MD
- Emery-Dreifuss MD
- Facioscapulohumeral MD
- Limb-girdle MD (some types)
- Myotonic MD
Other forms of MD are autosomal recessive. This means that both parents must carry the defective gene in order for the disorder to be passed to a child. In the case of autosomal recessive forms of MD, each parent is a “carrier” of one mutated gene but does not develop the disorder. When both parents are carriers of the gene mutation, there is a 25 percent chance of passing both copies of the mutated gene to their child. Forms of MD that are inherited in this way include:
- Congenital MD
- Distal MD
- Emery-Dreifuss MD
- Limb-girdle MD (some types)
A third type of inheritance pattern is called X-linked inheritance. This form is also called sex-linked inheritance because it involves the chromosomes that determine gender – specifically the male gender. Males inherit an X chromosome from their mother and a Y chromosome from their father. Females, on the other hand, inherit an X chromosome from each parent. Forms of MD that are X-linked are passed down from mother to son. Sons of mothers with a mutated X chromosome have a 50 percent chance of inheriting the gene mutation and the disorder. Fathers cannot pass mutated X chromosomes to their sons because the son inherits only a Y chromosome from his father. However, daughters of parents with mutated X chromosomes become carriers of the disease and, in rare cases, develop mild symptoms of MD, such as heart muscle weakness (cardiomyopathy) and some muscle weakness. MD forms linked to X-linked mutations include:
- Duchenne MD
- Becker MD
- Emery-Dreifuss MD
Signs and symptoms of muscular dystrophy
The signs and symptoms of muscular dystrophy (MD) vary with each type of the disease. All forms are characterized by progressive muscular weakness. They differ in which muscles are first affected and when the symptoms begin. Signs and symptoms of the many types of MD include:
|Disease||Location of Muscle Weakness||Other Signs and Symptoms|
|Duchenne MD||Body core and lower extremities||Loss of reflexes, waddling, clumsiness, difficulty rising from sitting or lying position, difficulty climbing stairs, posture changes, impaired breathing, enlarged calf muscles, curvature of spine, mild mental retardation|
|Myotonic MD||May start in feet, hands, lower legs and forearms. Progresses to facial and neck muscles||Inability to relax muscles following contraction (myotonia), difficulty swallowing, drooping eyelids, cataracts, frontal baldness, weight loss, mental impairment, drowsiness, fainting, dizziness, constipation, diarrhea, insulin resistance|
|Facioscapulohumeral MD||Starts in muscles around the eyes and mouth. Progresses to shoulders and chest||Impaired reflexes in arms, changes in facial appearance, difficulty swallowing and chewing, difficulty speaking, hearing loss|
|Becker MD||Symmetric in body core and lower extremities||Toe walking, frequent falls, difficulty rising from floor|
|Congenital MD||Present throughout body at birth||Inability to move joints freely, curvature of spine, respiratory and swallowing difficulties, foot and joint deformities|
|Emery-Dreifuss MD||Starts in upper arms and lower legs||Locked elbows, toe walking, rigid spine, facial weakness, muscle contractures|
|Limb-girdle MD||Starts in hips. Progresses to shoulders, legs and neck||Waddling, difficulty rising from chairs and climbing stairs, unable to carrying heavy objects, rigid spine|
|Distal MD||Starts in muscles in extremities||Unable to perform fine hand movements, difficulty extending fingers, difficulty walking and climbing stairs|
|Oculopharyngeal MD||Starts in facial and throat muscles. Progresses to shoulders and neck||Drooping eyelids, difficulty swallowing, change in voice, tongue atrophy, vision loss, difficulty walking and climbing stairs|
Diagnosis methods for muscular dystrophy
Muscular dystrophy (MD) is typically diagnosed using a physical examination in conjunction with the patient’s medical history and evidence of a family history of the disease. The physical examination will look for signs of muscle atrophy that correspond to the disease (e.g., replacement of muscle with fatty tissue). In addition, other tests are performed to rule out other causes of muscle weakness. Tests used to diagnose MD are likely to include:
- Blood and urine tests. Body fluids are analyzed for the quantities of aldolase, creatine kinase and myoglobin. High levels of these proteins and enzymes often indicate muscle damage before physical signs of MD appear. Blood cells may also be used for DNA tests that can identify mutations in the genes related to muscle proteins.
- Exercise tests. The patient may be requested to perform exercises for the physician and then examined after a period of rest. This allows the physician to assess muscle strength, respiratory capacity, and change in blood chemicals following exercise.
- Imaging tests. An MRI (magnetic resonance imaging) may be used to develop images that will show muscle quality, atrophy or abnormalities. MRIs can also indicate whether there has been a replacement of muscle tissue with fatty or connective tissue. Ultrasound may also be used to develop images of muscle tissue that may indicate certain abnormalities.
- Muscle biopsies. Taking small samples of muscle tissue allows physicians to monitor the course of MD and distinguish it from other diseases.
- Electromyogram (EMG). The electrical activity of muscles can be measured by inserting an electrode through the skin and into the target muscle. The patient is then asked to contract that muscle. If the patient’s activity pattern does not match normal patterns, it may be an indication that MD is affecting the body. This technique may also be used to determine the distribution of the disease in the body.
- Nerve conduction velocity (NCV) test. Similar to an electromyogram, this test uses an electrode and receiver attached to the skin to detect the ability of electrical signals to travel through nerves. An NCV test may also be used to rule out other potential causes of muscle weakness, such as nerve damage (neuropathy).
Treatment and prevention of MD
There is no cure for muscular dystrophy (MD). Its progression can not be stopped or prevented, but it can be slowed. This is one of the goals of most treatments. Treatment for MD also aims to keep the patient independent and mobile for as long as possible. Treatment can also help prevent or reduce the occurrence of painful deformities and life-threatening complications.
Medications may be prescribed to delay degeneration of the patient’s muscles. These often include corticosteroids or immunosuppressants, which must be taken over long periods. In addition, short-term medications may be prescribed to help control muscle spasms. Vitamin D supplements may also be recommended. These often help improve bone density and prevent fractures.
Some medications work to treat the delayed muscle relaxation associated with myotonic MD. These include medicines used to treat heart arrhythmia (mexiletine) and epilepsy (carbamazepine)
Other aspects of treatment may include:
- Physical therapy
- Orthopedic devices (e.g., braces, splints)
- Speech therapy
- Assisted ventilation
- Surgery to reduce cardiac issues, ease muscle contractions and correct scoliosis
In addition, regular physical exercise may help reduce patient’s symptoms and delay disease progression.
While there is no way to prevent MD, genetic counseling may be useful for couples with a family history of the disease. This may help determine the risk of a genetic mutation being passed to potential offspring.
Ongoing research about muscular dystrophy
Treatment of muscular dystrophy (MD) is a major subject of current medical research. To date, most treatment options that are available focus on reducing the symptoms of the disease. Researchers hope to discover ways to prevent and treat MD through understanding the disease and its causes.
Innovative treatment approaches for MD are being studied as possible cures for the disease. Many of these approaches use gene therapy. This type of therapy aims to replace mutated genes with properly functioning ones through cell transplants or by manipulating the patient’s cells. This has the potential of preventing or reversing the breakdown of muscles.
In addition to replacing genes, gene therapy may also be used to bypass certain gene mutations. This therapy may allow cells affected by MD to make the proper proteins required for muscle health.
While some researchers are trying to develop cures for MD, others continue to work on improving treatment of symptoms. Numerous medications are being studied that may reduce muscle degradation without harmful side effects.
Questions for your doctor regarding MD
Preparing questions in advance can help patients to have more meaningful discussions with healthcare professionalsregarding their condition. Patients may wish to ask their doctor the following muscular dystrophy-related questions:
- Am I at risk for MD?
- What type of MD do I have?
- What tests will you use to diagnose my disease?
- How will you treat my MD?
- Would I benefit from physical therapy? Can you recommend a physical therapist?
- What is the prognosis for my disease? What symptoms can I expect to experience?
- Will MD affect my lifespan?
- If I have a family history of MD, can I prevent the disease developing in myself or my children?
- If I have no family history of MD, why do you think I have the disease?
- Is there any ongoing research that may affect how my MD is treated?