What Causes Muscular Dystrophy?
What is Muscular Dystrophy?
Muscular dystrophy (MD) is a group of rare inherited muscle diseases
in which muscle fibers are unusually susceptible to damage. Muscles, primarily
your voluntary muscles, become progressively weaker. In the late stages
of muscular dystrophy, fat and connective tissue often replace muscle
fibers. In some types of muscular dystrophy, heart muscles, other involuntary
muscles and other organs are affected. There are many forms of muscular
dystrophy, some noticeable at birth (congenital muscular dystrophy), others
in adolescence (Becker MD), but the 3 most common types are Duchenne,
facioscapulohumeral, and myotonic. The various types of the disease affect
more than 50,000 Americans. There's no cure, but medications and therapy
can slow the course of the disease.
Duchenne MD - primarily affects boys and is the result
of mutations in the gene that regulates dystrophin - a protein involved
in maintaining the integrity of muscle fiber. Onset is between 3-5 years
and progresses rapidly. Most boys become unable to walk at 12, and by
20 have to use a respirator to breathe.
Becker-type muscular dystrophy - Like Duchenne dystrophy,
Becker-type muscular dystrophy is linked to the X chromosome, affects
dystrophin production, and occurs in males. However, the illness is about
10 times rarer than Duchenne, and it produces milder symptoms. Some people
seem to have a form of disease that is intermediate in severity between
Duchenne and Becker-type.
Facioscapulohumeral MD - appears in adolescence and causes
progressive weakness in facial muscles and certain muscles in the arms
and legs. It progresses slowly and can vary in symptoms from mild to disabling.
Limb-girdle muscular dystrophy - This form of muscular
dystrophy affects muscles of the shoulders and hips. It includes several
different illnesses, which can be inherited by both males and females.
Myotonic MD - varies in the age of onset and is characterized
by myotonia (prolonged muscle spasm) in the fingers and facial muscles;
a floppy-footed, high-stepping gait; cataracts; cardiac abnormalities;
and endocrine disturbances. Individuals with myotonic MD have long faces
and drooping eyelids; men have frontal baldness.
Symptoms of muscular dystrophy, as well as their age of onset, vary according
to the specific form of illness:
- Duchenne dystrophy - Signs and symptoms of Duchenne's
usually appear between the ages of 2 and 5. It first affects the muscles
of the pelvis, upper arms and upper legs. By late childhood, most children
with this form of muscular dystrophy are unable to walk. Most die by
their late teens or early 20s, often from pneumonia, respiratory muscle
weakness or cardiac complications. Some people with Duchenne's MD may
exhibit curvature of their spine (scoliosis).
- Becker-type muscular dystrophy - Signs and symptoms
of Becker's MD are similar to those of Duchenne's. The onset of the
signs and symptoms is generally later, from age 5 to 16
- Myotonic dystrophy - Muscle myotonia (abnormally
prolonged muscle contraction, with difficulty relaxing) may develop
soon after birth or begin as late as early adulthood, especially affecting
the hands, wrists and tongue. There also is wasting and weakening of
facial muscles, neck muscles, and muscles of the wrists, fingers and
ankles. Involvement of the tongue and throat muscles causes speech problems
and difficulty swallowing. If the diaphragm and chest muscle also are
involved, there may be breathing problems.
- Limb-girdle muscular dystrophy - Symptoms begin
in late childhood or early adulthood. They include progressive muscle
weakness in the shoulders and hips, together with breathing problems
(if the diaphragm is involved). If illness also affects the heart muscle,
there may be heart failure or abnormal heart rhythms.
- Facioscapulohumeral muscular dystrophy - Symptoms
may begin during infancy, late childhood, or early adulthood. Usually,
the first sign is facial weakness, with difficulty smiling, whistling
and closing the eyes. Later, there is difficulty raising the arms or
flexing the wrists and/or ankles.
Muscular dystrophy is a general term for a group of inherited diseases
involving a defective gene. Each form of muscular dystrophy is caused
by a genetic mutation that's particular to that type of the disease.
Duchenne's and Becker's muscular dystrophies are passed from mother to
son through one of the mother's genes in a pattern called X-linked recessive
inheritance. Boys inherit an X chromosome from their mother and a Y chromosome
from their father. The X-Y combination makes them male. Girls inherit
two X chromosomes, one from their mother and one from their father. The
X-X combination determines that they are female.
The defective gene that causes Duchenne's and Becker's muscular dystrophies
is located on the X-chromosome. Women who have the defective gene that
causes these muscular dystrophies are simply carriers and exhibit no signs
or symptoms of the disease. The disease can "skip" a generation
until another son inherits the defective gene on the X-chromosome. In
some cases of Duchenne's and Becker's muscular dystrophies, the disease
arises from a new mutation in a gene rather than from an inherited defective
Myotonic dystrophy is passed along in a pattern called autosomal dominant
inheritance. If either parent carries the defective gene for myotonic
dystrophy, there's a 50 percent chance the disorder will be passed along
to a child.
Some of the less common types of muscular dystrophy are passed along
in the same inheritance pattern that marks Duchenne's and Becker's muscular
dystrophies. Other types of muscular dystrophy can be passed on from generation
to generation and affect males and females equally. Still others require
a defective gene from both parents.
There is no cure for muscular dystrophy, although some drugs still in
the trial stage have shown promise in slowing or delaying the progression
of the disease. For the time being, treatment is aimed at preventing complications
due to the effects of weakness, decreased mobility, contractures, scoliosis,
heart defects and respiratory weakness.
Physical therapy: Physical therapy, especially regular
stretching, is important in helping to maintain the range of motion for
affected muscles and to prevent or delay contractures. Strengthening other
muscles to compensate for weakness in affected muscles may be of benefit
also, especially in earlier stages of milder MD. Regular exercise is important
in maintaining good, overall health, but strenuous exercise may damage
muscles further. For patients whose leg muscles are affected, braces may
help lengthen the period of time that they can walk independently.
Medications: Doctors prescribe medications to treat
some forms of muscular dystrophy:
- For myotonic dystrophy. The medications phenytoin
(Dilantin, Phenytek), quinine and procainamide (Pronestyl) may be
used to treat the delayed muscle relaxation that occurs in myotonic
- For Duchenne's muscular dystrophy. The anti-inflammatory
corticosteroid medication prednisone (Deltasone) may help improve
muscle strength and delay the progression of Duchenne's MD.
Occupational therapy: Occupational therapy involves
employing methods and tools to compensate for a patient’s loss of
strength and mobility. This may include modifications at home, dressing
aids, wheelchair accessories and communication aids.
Nutrition: Nutrition has not been shown to treat any
conditions of MD, but it is essential to maintaining good health.
Cardiac care: Arrhythmias are often a symptom with Emery-Dreifuss
and Becker MD and may need to be treated with special drugs. Pacemakers
may also be needed in some cases and heart transplants are becoming more
common for men with Becker MD.
Respiratory care: When the muscles of the diaphragm
and other respiratory muscles become too weak to function on their own,
a patient may require a ventilator to continue breathing deeply enough.
Air may also be administered through a tube or mouthpiece. It is therefore
very important to maintain healthy lungs to reduce the risk of respiratory
Surgery: To release the contractures that may develop
and that can position joints in painful ways, doctors can perform a tendon
release surgery. This may be done to relieve tendons of your hip and knee
and on the Achilles tendon at the back of your foot. Surgery may also
be needed to correct curvature of your spine.
MD Caregiver Well-Being
For family members of people with muscular dystrophy, coping with the
illness involves a major commitment of physical, emotional and financial
effort. The disease presents challenges in the classroom, in the home
and in all aspects of life.
In dealing with a disease such as muscular dystrophy, support groups
can be a valuable part of a wider network of social support that includes
health care professionals, family, friends and place of religious worship.
Support groups bring together people, family and friends who are coping
with the same kind of physical or mental health challenge. Support groups
provide a setting in which people can share their common problems and
provide ongoing support to one another.
Ask your doctor about self-help groups that may exist in your community.
Your local health department, public library, telephone book and the Internet
also may be good sources to locate a support group in your area.
The Muscular Dystrophy Association
3300 E. Sunrise Drive
Tucson, AZ 85718
Muscular Dystrophy Family Foundation
615 North Alabama Street Suite 330
Indianapolis IN 46204-1213