Muscular dystrophy is the name for a group of inherited disorders in which
strength and muscle bulk gradually decline. Nine types of muscular
dystrophies are generally recognized.
The muscular dystrophies include:
DMD occurs in about one in 3,500 male births and affects approximately
8,000 boys and young men in the United States. A milder form occurs in
very few female carriers.
BMD occurs in about one in 30,000 male births.
Fewer than 300 cases of EDMD have been identified.
The number of people affected with LGMD in the United States may be in the
FSH occurs in about one out of every 20,000 people and affects
approximately 13,000 people in the United States.
Myotonic dystrophy is the most common form of muscular dystrophy,
affecting more than 30,000 people in the United States.
OPMD is most common among French Canadian families in Quebec and in
Spanish-American families in the southwestern United States.
DD is most common in Sweden and rare in other parts of the world.
Fukuyama CMD is most common in Japan.
Causes and symptoms
Several of the muscular dystrophies, including DMD, BMD, CMD, and most
forms of LGMD, are due to defects in the genes for a complex of muscle
proteins. This complex spans the muscle cell membrane to unite a fibrous
network on the interior of the cell with a fibrous network on the outside.
As of 2004 the theory was that by linking these two networks, the complex
acts as a "shock absorber," redistributing and evening out
the forces generated by contraction of the muscle, thereby preventing
rupture of the muscle membrane. Defects in the proteins of the complex
lead to deterioration of the muscle. Symptoms of these diseases set in as
the muscle gradually exhausts its ability to repair itself. Both DMD and
BMD are caused by flaws in the gene for the protein called dystrophin. The
flaw leading to DMD prevents the formation of any dystrophin, while that
of BMD allows some protein to be made, accounting for the differences in
severity and onset between the two diseases. Differences among the other
diseases in the muscles involved and the ages of onset are less easily
The causes of the other muscular dystrophies are not as well understood:
The muscular dystrophies are genetic diseases, meaning they are caused by
defects in genes. Genes, which are linked together on chromosomes, have
two functions. They code for the production of proteins, and they are the
material of inheritance. Parents pass along genes to their children,
providing them with a complete set of instructions for making their own
Because both parents contribute genetic material to their offspring, each
child carries two copies of almost every gene, one from each parent. For
some diseases to occur, both copies must be flawed. Such diseases are
called autosomal recessive diseases. Some forms of LGMD and DD exhibit
this pattern of inheritance, as does CMD. A person with only one flawed
copy, called a carrier, will not have the disease but may pass the flawed
gene on to children. When two carriers have children, the chances of
having a child with the disease is one in four for each pregnancy.
Other diseases occur when only one flawed gene copy is present. Such
diseases are called autosomal dominant diseases. Other forms of LGMD
exhibit this pattern of inheritance, as do DM, FSH, OPMD, and some forms
of DD. When a person affected by the disease has a child with someone not
affected, the chances of having an affected child is one in two.
Because of chromosomal differences between the sexes, some genes are not
present in two copies. The chromosomes that determine whether a person is
male or female are called the X and Y chromosomes. A person with two X
chromosomes is female, while a person with one X and one Y is male. While
the X chromosome carries many genes, the Y chromosome carries almost none.
Therefore, a male has only one copy of each gene on the X chromosome, and
if it is flawed, he will have the disease that defect causes. Such
diseases are said to be X-linked. X-linked diseases include DMD, BMD, and
EDMD. Women are not usually affected by X-linked diseases, since they
will likely have one unaffected copy between the two chromosomes. Some
female carriers of DMD suffer a mild form of the disease, probably because
their one unaffected gene copy is shut down in some of their cells.
Women carriers of X-linked diseases have a one-in-two chance of passing
the flawed gene on to each child born. Daughters who inherit the disease
gene are carriers. A son born without the disease gene is free of the
disease and cannot pass it on to his children. A son born with the defect
has the disease. He will pass the flawed gene on to each of his daughters,
who will then be carriers, but to none of his sons (because they inherit
his Y chromosome).
Not all genetic flaws are inherited. As many as one-third of the cases of
DMD are due to new mutations that arise during egg formation in the
mother. New mutations are less common in other forms of muscular
All of the muscular dystrophies are marked by muscle weakness as the major
symptom. The distribution of symptoms, age of onset, and progression
is sometimes a symptom of each, usually due to the effects of weakness on
A boy with Duchenne muscular dystrophy usually begins to show symptoms as
a preschooler. The legs are affected first, making walking difficult and
causing balance problems. Most affected persons walk three to six months
later than expected and have difficulty running. Later on, the boy with
DMD will push his hands against his knees to rise to a standing position,
to compensate for leg weakness. About the same time, his calves will begin
to swell, though with fibrous tissue rather than with muscle and feel firm
and rubbery; this condition gives DMD one of its alternate names,
pseudohypertrophic muscular dystrophy. The boy will widen his stance to
maintain balance and walk with a waddling gait to advance his weakened
legs. Contractures (permanent muscle tightening) usually begin by age five
or six, most severely in the calf muscles. This pulls the foot down and
back, forcing the boy to walk on tip-toes, called equinus, and further
decreases balance. Frequent falls and broken bones are common beginning at
this age. Climbing stairs and rising unaided may become impossible by age
nine or ten, and most boys use a wheelchair for mobility by the age of 12.
Weakening of the trunk muscles around this age often leads to
(a side-to-side spine curvature) and kyphosis (a front-to-back
The most serious weakness of DMD is weakness of the diaphragm, the sheet
of muscles at the top of the abdomen that perform the main work of
breathing and coughing. Diaphragm weakness leads to reduced energy and
stamina and increased lung infection because of the inability to
effectively. Young men with DMD often live into their twenties and
beyond, provided they have mechanical ventilation assistance and good
About one third of boys with DMD experience specific learning
disabilities, including trouble learning by ear rather than by sight and
trouble paying attention to long lists of instructions. Individualized
educational programs usually compensate well for these disabilities.
The symptoms of BMD usually appear in late childhood to early adulthood.
Though the progression of symptoms may parallel that of DMD, the symptoms
are usually milder, and the course more variable. The same pattern of leg
weakness, unsteadiness, and contractures occurs later for the young man
with BMD, often allowing independent walking into the twenties or early
thirties. Scoliosis may occur but is usually milder and progresses more
slowly. Heart muscle disease (cardiomyopathy) occurs more commonly in BMD.
Problems may include irregular heartbeats (arrhythmias) and congestive
heart failure. Symptoms may include fatigue, shortness of breath, chest
. Respiratory weakness also occurs and may lead to the need for mechanical
This type of muscular dystrophy usually begins in early childhood, often
with contractures preceding muscle weakness. Weakness affects the shoulder
and upper arm originally, along with the calf muscles, leading to
foot-drop. Most men with EDMD survive into middle age, although a defect
in the heart's rhythm (heart block) may be fatal if not treated
with a pacemaker.
While there are at least six genes that cause the various types of LGMD,
two major clinical forms of LGMD are usually recognized. A severe
childhood form is similar in appearance to DMD but is inherited as an
autosomal recessive trait. Symptoms of adult-onset LGMD usually appear in
a person's teens or twenties and are marked by progressive weakness
and wasting of the muscles closest to the trunk. Contractures may occur,
and the ability to walk is usually lost about 20 years after onset. Some
people with LGMD develop respiratory weakness that requires use of a
ventilator. Lifespan may be somewhat shortened. (Autosomal dominant forms
usually occur later in life and progress relatively slowly.)
FSH varies in its severity and age of onset, even among members of the
. Symptoms most commonly begin in the teens or early twenties, though
infant or childhood onset is possible. Symptoms tend to be more severe in
those with earlier onset. The disease is named for the regions of the body
most severely affected by the disease: muscles of the face (facio-),
shoulders (scapulo-), and upper arms (humeral). Hips and legs may be
affected as well. Children with FSH often develop partial or complete
The first symptom noticed is often difficulty lifting objects above the
shoulders. The weakness may be greater on one side than the other.
Shoulder weakness also causes the shoulder blades to jut backward, called
scapular winging. Muscles in the upper arm often lose bulk sooner than
those of the forearm, giving a "Popeye" appearance to the
arms. Facial weakness may lead to loss of facial expression, difficulty
closing the eyes completely, and inability to drink through a straw, blow
up a balloon, or whistle. A person with FSH may not develop strong facial
wrinkles. Contracture of the calf muscles may cause foot-drop, leading to
frequent tripping over curbs or rough spots. People with earlier onset
often require a wheelchair for mobility, while those with later onset
Symptoms of myotonic dystrophy include facial weakness and a slack jaw,
drooping eyelids (ptosis), and muscle wasting in the forearms and calves.
A person with this dystrophy has difficulty relaxing his grasp, especially
if the object is cold. Myotonic dystrophy affects heart muscle, causing
arrhythmias and heart block, and the muscles of the digestive system,
leading to motility disorders and
. Other body systems are affected as well: myotonic dystrophy may cause
cataracts, retinal degeneration, low IQ, frontal balding, skin disorders,
apnea, and insulin resistance. An increased need or desire for sleep is
common, as is diminished motivation. Severe disability affects most people
with this type of dystrophy within 20 years of onset, although most do not
require a wheelchair even late in life.
OPMD usually begins in a person's thirties or forties, with
weakness in the muscles controlling the eyes and throat. Symptoms include
drooping eyelids, difficulty swallowing (dysphagia), and weakness
progresses to other muscles of the face, neck, and occasionally the upper
limbs. Swallowing difficulty may cause aspiration or the introduction of
food or saliva into the airways.
DD usually begins in the twenties or thirties with weakness in the hands,
forearms, and lower legs.
Difficulty with fine movements such as typing or fastening buttons may be
the first symptoms. Symptoms progress slowly, and the disease usually does
not affect life span.
CMD is marked by severe muscle weakness from birth, with infants
displaying "floppiness" and very little voluntary movement.
Nonetheless, a child with CMD may learn to walk, either with or without
some assistive device, and live into young adulthood or beyond. In
contrast, children with Fukuyama CMD are rarely able to walk and have
severe mental retardation. Most children with this type of CMD die in
A doctor should be consulted whenever muscle development is thought to be
abnormal or slow.
Diagnosis of muscular dystrophy involves a careful medical history and a
thorough physical exam to determine the distribution of symptoms and to
rule out other causes. Family history may give important clues, since all
the muscular dystrophies are genetic conditions (though no family history
will be evident in the event of new mutations).
Lab tests may include the following:
For most forms of muscular dystrophy, accurate diagnosis is not difficult
when done by someone familiar with the range of diseases. There are
exceptions, however. Even with a muscle biopsy, it may be difficult to
distinguish between FSH and another muscle disease, polymyositis.
Childhood-onset LGMD is often mistaken for the much more common DMD,
especially when it occurs in boys. BMD with an early onset appears very
similar to DMD, and a muscle biopsy may be needed to accurately
distinguish them. The muscular dystrophies may be confused with diseases
involving the motor neurons, such as
spinal muscular atrophy
; diseases of the neuromuscular junction, such as myasthenia gravis; and
other muscle diseases, as all involve generalized weakening of varying
As of 2004 there were no cures for any of the muscular dystrophies.
Prednisone, a corticosteroid, has been shown to delay the progression of
DMD somewhat, for reasons that as of 2004 are still unclear. Prednisone is
also prescribed for BMD.
Treatment of muscular dystrophy is mainly directed at preventing the
complications of weakness, including decreased mobility and dexterity,
contractures, scoliosis, heart defects, and respiratory insufficiency.
Physical therapy, in particular regular stretching, is used to maintain
the range of motion of affected muscles and to prevent or delay
contractures. Braces are used as well, especially on the ankles and feet
to prevent equinus. Full-leg braces may be used in DMD to prolong the
period of independent walking. Strengthening other muscle groups to
compensate for weakness may be possible if the affected muscles are few
and isolated, as in the earlier stages of the milder muscular dystrophies.
helps maintain general good health. Strenuous exercise is usually not
recommended, since it may damage muscles further.
When contractures become more pronounced, tenotomy surgery may be
performed. In this operation, the tendon of the contractured muscle is
cut, and the limb is braced in its normal resting position while the
tendon regrows. In FSH, surgical fixation of the scapula can help
compensate for shoulder weakness. For a person with OPMD, surgical lifting
of the eyelids may help compensate for weakened muscular control. For a
person with DM, sleep apnea may be treated surgically to maintain an open
airway. Scoliosis surgery is often needed in DMD but much less often in
other muscular dystrophies. Surgery is recommended at a much lower degree
of curvature for DMD than for scoliosis due to other conditions, since the
decline in respiratory function in DMD makes surgery at a later time
dangerous. In this surgery, the vertebrae are fused together to maintain
the spine in the upright position. Steel rods are inserted at the time of
operation to keep the spine rigid while the bones grow together.
When any type of surgery is performed in people with muscular dystrophy,
anesthesia must be carefully selected. People with MD are susceptible to a
severe reaction, known as malignant hyperthermia, when given halothane
The occupational therapist suggests techniques and tools to compensate for
the loss of strength and dexterity. Strategies may include modifications
in the home, adaptive utensils and dressing aids, compensatory movements
and positioning, wheelchair accessories, or communication aids.
helps to promote general health in all the muscular dystrophies. No
special diet or supplement has as of 2004 been shown to be of use in any
the conditions. The weakness in the throat muscles seen especially in
OPMD and later DMD may necessitate the use of a gastrostomy tube, inserted
in the stomach to provide nutrition directly.
The arrhythmias of EDMD and BMD may be treatable with antiarrhythmia drugs
such as mexiletine or nifedipine. A pacemaker may be implanted if these do
not provide adequate control. Heart transplants are increasingly common
for men with BMD.
—A pattern of inheritance in which only one of the two copies of
an autosomal gene must be abnormal for a genetic condition or disease to
occur. An autosomal gene is a gene that is located on one of the
autosomes or non-sex chromosomes. A person with an autosomal dominant
disorder has a 50 percent chance of passing it to each of their
—A pattern of inheritance in which both copies of an autosomal
gene must be abnormal for a genetic condition or disease to occur. An
autosomal gene is a gene that is located on one of the autosomes or
non-sex chromosomes. When both parents have one abnormal copy of the
same gene, they have a 25 percent chance with each pregnancy that their
offspring will have the disorder.
Becker muscular dystrophy (BMD)
—A type of muscular dystrophy that affects older boys and men and
usually follows a milder course than Duchenne muscular dystrophy.
—A tightening or shortening of muscles that prevents normal
movement of the associated limb or other body part.
Distal muscular dystrophy (DD)
—A form of muscular dystrophy that usually begins in middle age
or later, causing weakness in the muscles of the feet and hands.
Duchenne muscular dystrophy (DMD)
—The most severe form of muscular dystrophy, DMD usually affects
young boys and causes progressive muscle weakness, usually beginning in
—A protein that helps muscle tissue repair itself. Both Duchenne
muscular dystrophy and Becker muscular dystrophy are caused by flaws in
the gene that tells the body how to make this protein.
Facioscapulohumeral muscular dystrophy (FSH)
—This form of muscular dystrophy, also known as Landouzy-Dejerine
disease, begins in late childhood to early adulthood and affects both
men and women, causing weakness in the muscles of the face, shoulders,
and upper arms.
Limb-girdle muscular dystrophy (LGMD)
—A form of muscular dystrophy that begins in late childhood to
early adulthood and affects both men and women. It causes weakness in
the muscles around the hips and shoulders.
—A form of muscular dystrophy, also known as Steinert's
disease, that affects both men and women. It is characterized by delay
in the ability to relax muscles after forceful contraction (myotonia)
and wasting of muscles, as well as other abnormalities.
Oculopharyngeal muscular dystrophy
—A type of muscular dystrophy that affects adults of both sexes,
causing weakness in the eye muscles and throat.
Two experimental procedures aiming to cure DMD have attracted a great deal
of attention. In myoblast transfer, millions of immature muscle cells are
injected into an affected muscle. The goal of the treatment is to promote
the growth of the injected cells, replacing the
defective host cells with healthy new ones. Despite continued claims to
the contrary by a very few researchers, this procedure is widely judged a
Gene therapy introduces good copies of the dystrophin gene into muscle
cells. The goal is to allow the existing muscle cells to use the new gene
to produce the dystrophin it cannot make with its flawed gene. Problems
have included immune rejection of the virus used to introduce the gene,
loss of gene function after several weeks, and an inability to get the
gene to enough cells to make a functional difference in the affected
muscle. Nonetheless, after a number of years of refining the techniques in
mice, researchers began human trials in 1998. These trials are ongoing.
The expected life span for a male with DMD has increased significantly
since the 1970s. Most young men live into their early or mid-twenties.
Respiratory infections become an increasing problem as their breathing
becomes weaker, and these infections are usually the cause of death.
The course of the other muscular dystrophies is more variable; expected
life spans and degrees of disability are hard to predict but may be
related to age of onset and initial symptoms. Prediction is made more
difficult because, as new genes are discovered, it becomes clear that
several of the dystrophies are not uniform disorders but rather symptom
groups caused by different genes.
People with dystrophies with significant heart involvement (BMD, EDMD,
Myotonic dystrophy) may nonetheless have almost normal life spans,
provided that cardiac complications are monitored and treated
aggressively. The respiratory involvement of BMD and LGMD similarly
require careful and prompt treatment.
As of 2004 there was no way to prevent any of the muscular dystrophies in
a person who has the genes responsible for these disorders. Accurate
genetic tests, including prenatal tests, are available for some of the
muscular dystrophies. Results of these tests may be useful for purposes of
There is no known link between nutrition and the onset of muscular
Prospective parents with first-degree relatives (parents, siblings, or
other children) who have been diagnosed with muscular dystrophy should
consider including counseling in their family planning process.
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