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Muscular dystrophy (MD) is a genetic disorder that gradually weakens the body’s muscles. It’s caused by incorrect or missing genetic information that prevents the body from making the proteins needed to build and maintain healthy muscles.
A child who is diagnosed with MD gradually loses the ability to do things like walk, sit upright, breathe easily, and move the arms and hands. This increasing weakness can lead to other health problems.
There are several major forms of muscular dystrophy, which can affect the muscles to varying degrees. In some cases, MD starts causing muscle problems in infancy; in others, symptoms don’t appear until adulthood.
There is no cure for MD, but researchers are quickly learning more about how to prevent and treat it. Doctors are also working on improving muscle and joint function and slowing muscle deterioration so that those with MD can live as actively and independently as possible.
Many kids with muscular dystrophy follow a normal pattern of development during their first few years of life. But in time common symptoms begin to appear. A child who has MD may start to stumble, waddle, have difficulty going up stairs, and toe walk (walk on the toes without the heels hitting the floor). A child may start to struggle to get up from a sitting position or have a hard time pushing things, like a wagon or a tricycle.
Kids with MD often develop enlarged calf muscles (called calf pseudohypertrophy) as muscle tissue is destroyed and replaced by fat.
Diagnosis
When first suspecting that a child has muscular dystrophy, a doctor will do a physical exam, take a family history, and ask about any problems – particularly those affecting the muscles – that the child might be having.
In addition, the doctor may perform tests to determine what type of MD is involved and to rule out other diseases that could cause the problem. These might include a blood test to measure levels of serum creatine kinase, an enzyme that’s released into the bloodstream when muscle fibers are deteriorating. Elevated levels indicate that something is causing muscle damage.
The doctor also may do a blood test to check the DNA for gene abnormalities or a muscle biopsy to examine a muscle tissue sample for patterns of deterioration and abnormal levels of dystrophin, a protein that helps muscle cells keep their shape and length. Without dystrophin, the muscles break down.
Types of Muscular Dystrophy
The different types of muscular dystrophy affect different sets of muscles and result in different degrees of muscle weakness.
Duchenne muscular dystrophy is the most common and the most severe form of MD. It affects about 1 out of every 3,500 boys. (Girls can carry the gene that causes the disease, but they usually have no symptoms.) This form occurs because of a problem with the gene that makes dystrophin. Without this protein, the muscles break down and a child becomes weaker.
In cases of Duchenne muscular dystrophy, symptoms usually begin to appear around age 5, as the pelvic muscles begin to weaken. Most kids with this form need to use a wheelchair by age 12. Over time, their muscles weaken in the shoulders, back, arms, and legs.
Eventually, the respiratory muscles are affected, and a ventilator is required to assist breathing. Kids who have Duchenne MD typically have a life span of about 20 years.
Although most kids with Duchenne muscular dystrophy have average intelligence, about one-third of them experience learning disabilities and a small number have mental retardation.
While the incidence of Duchenne is known, it’s unclear how common other forms of MD are because the symptoms can vary so widely between individuals. In fact, in some people the symptoms are so mild that the disease goes undiagnosed.
Becker muscular dystrophy is similar to Duchenne, but it is less common and progresses more slowly. This form of MD affects approximately 1 in 30,000 boys. It too is caused by insufficient production of dystrophin.
Symptoms begin during the teen years, then follow a pattern similar to Duchenne MD. Muscle weakness first begins in the pelvic muscles, then moves into the shoulders and back. Many children with Becker MD have a normal life span and can lead long, active lives without the use of a wheelchair.
Myotonic dystrophy, also known as Steinert’s disease, is the most common adult form of MD, although half of all cases are diagnosed in people under 20 years old. It is caused by a portion of a particular gene that is larger than it should be. The symptoms can appear at any time during a child’s life.
The main symptoms include muscle weakness, myotonia (in which the muscles have trouble relaxing once they contract), and muscle wasting, where the muscles shrink over time. Kids with myotonic dystrophy also can experience cataracts and heart problems.
Limb-girdle muscular dystrophy affects boys and girls equally. Symptoms usually begin when kids are between 8 and 15 years old. This form progresses slowly, affecting the pelvic, shoulder, and back muscles. The severity of muscle weakness varies – some kids have only mild weakness while others develop severe disabilities and as adults need to use a wheelchair.
Facioscapulohumeral muscular dystrophy can affect both boys and girls, and the symptoms usually first appear during the teen years. It tends to progress slowly.
Muscle weakness first develops in the face, making it difficult for a child to close the eyes, whistle, or puff out the cheeks. The shoulder and back muscles gradually become weak, and kids have difficulty lifting objects or raising their hands overhead. Over time, the legs and pelvic muscles also may lose strength.
Other types of MD, which are rare, include distal, ocular, oculopharyngeal, and Emery-Dreifuss.