What is muscular dystrophy?
Muscular dystrophy is a group of genetic disorders that affect the muscles. These rare diseases cause muscular weakness and degeneration. They mainly affect voluntary skeletal muscles that control movement. Some of them also involve involuntary muscles, such as the heart and muscles in the respiratory and digestive tracts.
Abnormal genes cause muscular dystrophy. The genes involved make proteins necessary for normal, healthy muscles. A different gene is responsible for each of the muscular dystrophy types. These genes can be passed from parents to children. The genetic abnormality may also develop spontaneously during development in the womb.
Muscle weakness is the main symptom of these disorders. The specific muscular dystrophy symptoms vary with the forms of the disorder and the muscles they affect. All of them are progressive, meaning they get worse with time.
The muscular dystrophy types differ in the age of onset (when symptoms begin), affected muscles, severity, and rate of progression. Some develop in childhood, while others do not begin until adulthood. They also differ in the pattern of inheritance—or how people inherit the genes. The pattern of inheritance determines who the disease affects and who is just a genetic carrier.
There are more than 30 muscular dystrophy types. The most common forms of muscular dystrophy include:
Duchenne muscular dystrophy is the most common type. It mainly affects boys between the ages of 3 and 5 years. In affected families, there is a 50% chance that girls will carry the gene and pass it on to their sons. Girls rarely have symptoms of the disorder.
Becker muscular dystrophy is similar to Duchenne. However, it is milder, progresses slower, and tends to develop in males during teenage years.
Facioscapulohumeral muscular dystrophy (FSHD) affects boys and girls equally. It typically develops during the teenage years or early 20s.
Myotonic muscular dystrophy also affects males and females equally. It most commonly strikes people between the ages of 10 and 30. However, it can begin during infancy or old age.
There is no cure for muscular dystrophy. Medications can help ease symptoms and may slow progression. Various forms of therapy can also be useful for managing symptoms.
See your doctor if you notice any problems with muscle weakness, mobility, or difficulty with everyday tasks. Doctors routinely check developmental progress in children during well-child visits. This routine medical care can identify potential problems. However, you should contact your child’s doctor for concerns between visits.
What are the symptoms of muscular dystrophy?
Muscular dystrophy causes progressive muscle weakness and deterioration. When it affects skeletal muscle, it leads to problems with movement and mobility. Some forms of muscular dystrophy also affect muscles involved in involuntary functions, such as breathing. These disorders lead to problems with bodily functions and processes vital for life. The severity of symptoms and the rate of progression vary with the type of muscular dystrophy.
Common symptoms of Duchenne muscular dystrophy
Duchenne muscular dystrophy mainly affects the muscles of the arms, legs and pelvis and progresses rapidly. The most common symptoms are:
Difficulty walking, climbing stairs, running or jumping, which progresses to most boys being unable to walk by age 12
Enlarged calf muscles
Frequent falls and stumbles
Gait changes including waddling gait and walking on the toes
Learning disabilities and mental developmental delays
Muscle pain and stiffness
Trouble rising from a lying or seated position
Common symptoms of Becker muscular dystrophy
Becker muscular dystrophy is similar to Duchenne, but milder and with a slower progression. It affects the same muscles and results in the same physical effects. However, the disease progresses over decades instead of years. Males with the disorder may only need assistance from canes or walkers. Some will require wheelchairs by middle age.
Common symptoms of FSHD
FSHD affects muscles of the face, shoulders, arms and legs. It progresses very slowly, with some people going decades before noticeable symptoms appear. Common symptoms include:
Difficulty reaching over the head or with throwing motions
Shoulder blades that stick out like wings
Trouble drinking through a straw, blowing up a balloon, or whistling
Common symptoms of myotonic dystrophy
Myotonic dystrophy affects muscles of the face, neck, arms, hands, hips and legs. The specific symptoms and their severity vary with the age of onset. Symptoms also depend on the subtype—DM1 or DM2. In general, myotonia is the main characteristic of this disorder. Myotonia means the person can’t relax muscles at will. For example, it may be difficult to let go of something once the person has grasped it. The disease can also involve muscles that control bodily functions, such as digestion. The progression of this disorder varies, but is usually slow.
Depending on the type of muscular dystrophy, symptoms may become obvious quickly or develop over decades. Regular medical care, including well-child visits, are important for screening for muscle problems. If you notice symptoms of muscle weakness between regular visits, contact your doctor. Early diagnosis can help slow the progression of symptoms and complications.
What causes muscular dystrophy?
The muscular dystrophies are genetic disorders. They involve genes that are responsible for making proteins necessary for normal, healthy muscles. Defects, or mutations in these genes result in muscle weakness and degeneration. Each form of muscular dystrophy has its own genetic mutation. In most cases, the mutation passes from parent to child. This is an inherited mutation. Sometimes, the mutation happens by accident during development before birth. This is a spontaneous mutation.
What are the risk factors for muscular dystrophy?
The various forms of muscular dystrophy affect both sexes, all ages, and all races. The most common form, Duchenne muscular dystrophy, typically affects boys between the ages of 3 and 5 years.
Because muscular dystrophy is usually inherited, the risk is higher in families with a history of it. However, each form of muscular dystrophy has its own inheritance pattern:
Duchenne MD is X-linked recessive. This means the gene is located on the X chromosome and women with the mutation are carriers. Carriers rarely have symptoms of the disorder themselves and probably do not know they carry the mutated gene. They have a 50% chance of passing the disorder to their sons. There is also a 50% chance of passing their carrier status to their daughters.
Becker MD is also X-linked recessive.
FSHD is autosomal dominant. This means if you inherit the mutated gene you will have the disorder. The gene can come from either parent.
Myotonic is also autosomal dominant.
Reducing your risk of muscular dystrophy
Currently, there is no way of preventing muscular dystrophy. However, genetic testing can assist individuals, couples and families in planning their future. Carrier testing can identify people at risk of passing the mutation or the disorder to their children. This can help people make decisions about having biological children or not. Knowing the specific mutation in someone who has the disorder may also be helpful as new therapies are available.
Issues surrounding genetic testing are complex. It is important to work with a genetic counselor if you decide to go this route. A counselor can help you fully understand the implications of testing and provide guidance.
How is muscular dystrophy treated?
Doctors do not have a way to cure muscular dystrophy today. But finding the disease early can help slow the progression. Muscular dystrophy treatments may include:
Assistive devices, such as canes, walkers and wheelchairs help with mobility and maintain independence.
Braces keep muscles and tendons stretched and support weak muscles.
Corticosteroids may help improve muscle strength and delay progression of some forms. However, long-term use can cause problems, especially with bones.
Eteplirsen (Exondys 51) may increase muscle strength in people with Duchenne. It is for people with a specific mutation, but its effectiveness is still unclear.
Heart medications support circulation when heart damage is present.
Physical therapy increases muscle strength, flexibility, and range of motion.
Surgery may be necessary in some cases. It can release muscle tension and correct spinal curvatures.
What are the potential complications of muscular dystrophy?
Muscular dystrophy is progressive. It will worsen with time and cause complications. Most boys with Duchenne will need a wheelchair by the age of 12. Muscular dystrophy can cause contractures—shortening of the muscles and tendons around a joint. A curved spine can also develop due to weakened support muscles. Both of these complications will further limit mobility.
When muscular dystrophy affects involuntary muscles, several complications can develop. As the disease progresses, breathing can become difficult. Eventually, a ventilator may be necessary to assist with the work of breathing. Similarly, swallowing problems can develop due to muscle weakness. A feeding tube may be necessary to provide nutrition. Heart problems can be an issue as well. A weakened heart muscle may struggle to pump blood effectively to the rest of the body.
Life expectancy for the most common form—Duchenne—has increased dramatically in recent years. In the past, boys could only expect to live through their teens. Today, it is common for men with access to good medical care and a support team (family, friends and caregivers) to survive into their 30s and even beyond.
The rate of progression varies with the type of muscular dystrophy and other factors. Healthcare providers who help people with neuromuscular diseases like MD include neurologists, physiatrists (physical medicine and rehabilitation), neuromusculoskeletal experts, physical therapists, orthopedic specialists, and occupational therapists. Other specialists like cardiologists may be necessary depending on the specific problems the disease causes.