Fundraising telethons and vague images of disabled children loom in most parents’ minds when they hear the words “muscular dystrophy.” The truth is that rapid advances in molecular genetic engineering hold promise for children with muscular dystrophy. Support of these efforts makes good sense.
The muscular dystrophies are a group of illnesses that share several things in common. They are all, first and foremost, muscle diseases as opposed to brain or nerve diseases. They all involve the death of individual muscle fibers. They are all hereditary conditions. And they all progress over time (as opposed to cerebral palsy, which doesn’t get worse or better).
Duchenne muscular dystrophy is the most common of the muscular dystrophies. It is an X-linked recessive condition, so it occurs in boys whose mothers are carriers. It appears around the world in all ethnic groups. Becker muscular dystrophy is a milder form of the same condition.
Emery-Dreifuss muscular dystrophy is a very rare form of muscular dystrophy that is also an X-linked recessive condition, with affected boys born to mothers who are carriers.
Myotonic muscular dystrophy (Steinert disease) is the second most common type. It is found most often in North America, Europe, and Australia. It is an autosomal dominant condition, which means that when one of the parents has the condition, about half of the children will (both boys and girls). There are no carriers without the illness.
Facioscapulohumeral muscular dystrophy (Landouzy-Dejerine disease) is a very rare form of muscular dystrophy that is also an autosomal dominant condition. When a parent has the condition, about half of the children will. There are no carriers without the illness.
Congenital muscular dystrophy and limb-girdle muscular dystrophy are autosomal recessive conditions. If both of the parents are carriers, about half of the children will be carriers, and about one-fourth of the children will have the disease. If only one parent is a carrier, the disease is not passed on, but about one-fourth of the children will be carriers.
The Fukuyama type of congenital muscular dystrophy is especially common in Japan, but is also found in Europe and the Middle East.
The hallmark symptom of muscular dystrophy is progressive muscle weakness. In classic Duchenne muscular dystrophy, the boys appear normal at birth. Looking back, perhaps they had poor head control compared to their peers. Nevertheless, they roll over, sit, stand, and walk at a typical age. By age 3, the weakness is clear. They will often need to walk their hands up their legs in order to stand up (the Gower sign). They tend to have large calves, and waddle when they walk. With aggressive treatment, most can walk until about age 12, but death usually occurs before adulthood. These boys often also have heart disease. Learning disability or mental retardation are some of the many other symptoms common in this condition.
Becker muscular dystrophy is a milder form of the same condition. The progressive course may take more than twice as long, but the progress is still relentless.
Children with limb-girdle muscular dystrophy appear normal until the school years or even into young adulthood. Weakness develops first in the muscles close to the trunk–around the shoulders and hips. Most can walk until about age 30. Enlargement of the calf muscles is also common in this condition. Intellectual growth is normal.
Children with Enery-Dreifuss muscular dystrophy usually appear healthy until school age. Weakness around the elbows and the ankles is often the first sign. Enlargement of the calf muscles does not occur. Intellectual growth is normal.
Children with congenital muscular dystrophies are noticeably weak at the time of birth. Nevertheless, these tend to be milder forms of muscular dystrophy with a slowly progressive course.
Facioscapulohumeral muscular dystrophy also appears in young babies. The earliest signs are weakness of the face and shoulder muscles. The eyes are often open during sleep.
Myotonic muscular dystrophy may also have symptoms in the first few years, including an upper lip shaped like an upside-down V. Muscles of the face and fingers usually show weakness first.
Depending on the type of muscular dystrophy, complications may also include cataracts, diabetes, heart disease, hypothyroidism, immunodeficiency, mental retardation, scoliosis, seizures, or testicular atrophy.
The muscular dystrophies are all lifelong, progressive conditions. Some, such as Duchenne muscular dystrophy, usually lead to death in late childhood, while others, such as Becker muscular dystrophy, commonly allow people to live to age 40.
The diagnosis is made by muscle biopsy. It is suspected by the history and physical exam, and by lab tests, such as one for a muscle enzyme called CK. An electromyogram (EMG) is a test of the electrical activity in muscles that may be used to evaluate nerve and muscle conditions.
So far, there is no cure for the muscular dystrophies. Aggressive treatment is important to prevent and manage complications. This may include physical therapy and nutritional support. Meanwhile, scientists are searching for a cure or at least for ways to slow progression. Molecular genetic engineering seems to hold the most promise (Expert Opinion on Biological Therapy. 8(8):1051-61, 2008 Aug.).
One of the best summaries of research on muscular dystrophies can be found on the website of the National Institute of Neurological Disorders and Stroke, part of the NIH.
They note that current research can be divided into several categories:
Once a child has been conceived with the genes for muscular dystrophy, the disease cannot be prevented.
The Gower Sign, Landouzy-Dejerine Disease, Steinert Disease.