What Is Muscular Dystrophy?
Doctors explain the symptoms and causes of the types of muscular dystrophy that affect children.
Muscular dystrophy, a group of rare genetic diseases, affects people of all ages and races, and both genders -- approximately one quarter of a million people in the United States.
The diseases are caused by defective genes that weaken and break down muscle fibers over time. The genetic mutation is often passed down from one generation to the next, but there are also cases of muscular dystrophy with no family history.
Muscular dystrophy (MD) primarily affects skeletal muscles in the arms, legs, and trunk. As muscle mass and strength decrease, people with muscular dystrophy may lose the ability to walk and reach over their heads; eventually they may need support to sit. In some cases, MD starts to affect involuntary muscles, including those in the heart and gut. People in the advanced stages of MD may have trouble with breathing, swallowing, and other basic functions.
There is currently no cure, but good medical management, including attention to complications and medication to ease symptoms can help slow its effects. "I'm hopeful that we're going to see some [new] drugs on the market in the next five to ten years -- perhaps sooner," says Valerie A. Cwik, M.D., executive vice president and chief medical and scientific officer of the Muscular Dystrophy Association in Tucson.
For now, the corticosteroid prednisone has been shown to slow muscle deterioration in boys with Duchenne muscular dystrophy, sometimes allowing them to walk for up to three extra years. Physical therapy can also help patients stay on their feet longer. As the diseases progress, those affected may need to use mobility aids, including leg braces, walkers, and wheelchairs.
There are many types of muscular dystrophy. Some develop in infancy and childhood; others don't surface until adulthood. Each type varies in severity, rate of progression, and order of muscle groups affected. These are some of the main types affecting infants and children:
Duchenne muscular dystrophy accounts for roughly half of all childhood muscular dystrophy. It affects young boys almost exclusively. "Duchenne is one of the most common rare diseases that we deal with," says Darryl De Vivo, M.D., pediatric neurologist in the Pediatric Neuromuscular Disease Center at Columbia University Medical Center/NewYork-Presbyterian. It affects about 1 in 3,500 to 1 in 5,000 newborn male infants. Symptoms include late walking, enlarged calf muscles, clumsiness, frequent falls, and difficulty climbing stairs or getting up off the floor. The symptoms usually appear between ages 3 and 5. The areas affected typically first include the muscles of the hips, pelvis, thighs, and shoulders. Weakening of the arms, legs, and trunk muscles follows. The progression is relatively rapid. By their early teens, boys with Duchenne muscular dystrophy usually require a wheelchair and have related heart and respiratory issues. Duchenne muscular dystrophy shortens life, but many children live into their mid-twenties and some into their thirties and beyond.
Becker muscular dystrophy is similar to Duchenne muscular dystrophy but it is milder and its symptoms may not appear until later in childhood or adolescence. It primarily affects boys and shares many of the same symptoms as Duchenne muscular dystrophy. Becker muscular dystrophy progresses more slowly and less predictably than Duchenne. People affected typically live until mid- to late-adulthood.
Congenital muscular dystrophy refers to several types of the genetic disease that are diagnosed at birth or before age 2. The disorders vary in symptoms, severity, and rate of progression, but in general, babies and children with congenital muscular dystrophy have low muscle tone. Symptoms can also include a curved spine, trouble breathing, intellectual and learning disabilities, eye defects, and seizures. The life expectancy varies greatly. Children with the most severe forms may live into their teens or early twenties. Children with milder forms may live longer.
Limb-Girdle muscular dystrophy has many forms, including childhood forms. The disorder causes weakness in muscles in the hip and shoulder areas. Children may have trouble climbing stairs, standing from a sitting position, and walking. The severity varies. Those affected do not usually have a shortened life expectancy.
Congenital Myotonic muscular dystrophy is relatively rare in children. Babies with the disease have weak muscle tone, often have serious breathing problems, and may have an inward or upward turning foot, known as clubfoot. They may have delayed development and intellectual disabilities. Although some babies face life-threatening complications from respiratory distress and failure to thrive at birth, the majority overcome those challenges, Dr. Cwik says. Muscle-related symptoms may stabilize in childhood. Myotonic muscular dystrophy may appear in childhood, adolescence, or adulthood; cardiac complications are a common feature in adults with myotonic dystrophy, regardless of when the disease first appeared. The heart should be monitored regularly, as cardiac arrhythmias may be life-threatening.
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