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MUSCULAR DYSTROPHY
What is muscular dystrophy?
The term "muscular dystrophy" actually refers to a group of
degenerative muscle diseases characterized by gradual weakening and
deterioration of skeletal muscles, and sometimes the heart and respiratory
muscles. Children with the disease are born with an abnormal genetic trait that
causes their muscles to develop improperly. The most common types of muscular
dystrophy result in dramatic physical weakness, so children lose the ability to
do things like walk, sit upright, breathe easily, and move their arms and
hands. The increasing weakness often leads to other serious complications and,
for many, a shortened life span. Other forms can result in relatively minor
physical disabilities or develop late in life, allowing affected people to have
fairly normal life spans and activity levels.
In most cases, the genetic abnormality for muscular dystrophy is inherited,
so the condition tends to run in families. Some types of muscular dystrophy,
including Duchenne, are X-linked, which means that the abnormality is carried
on the X chromosome that the mother contributes. A girl receives two X
chromosomes, one from each parent, while a boy receives a Y chromosome from the
father and an X from the mother. As a result, it is almost always boys who
develop symptoms; girls inherit a normal X chromosome that may "cancel
out" the abnormal one. Girls who carry the abnormal gene have a 50% chance
of passing the condition to their sons.
The different types of muscular dystrophy affect different sets of muscles
and result in different degrees of muscle weakness.
What are the first symptoms of muscular dystrophy?
Dr. Harold Marks, a neurologist specializing in muscular dystrophy at the
duPont Hospital for Children in Wilmington, DE, says that many parents first
learn of a potential problem from a teacher who notices that their child just
"isn't as active as other children."
The symptoms of Duchenne usually appear between the ages of two and five.
Parents may notice that their child stumbles more frequently, waddles, has
difficulty going up stairs, and toe-walks. Toddlers may develop a swayed back
to compensate for weakening hip-area muscles. Children may struggle to get up
from a sitting position. Many children also develop enlarged calf muscles, a
condition called calf pseudohypertrophy, as muscle tissue is destroyed and
replaced by non-muscle tissue.
Symptoms can first appear during early childhood or late adult life,
depending on the type of muscular dystrophy a child develops. For example, the
symptoms of Becker dystrophy are similar to Duchenne, but they may start during
the school-age years, are less severe, and allow children to live well into
adulthood. In contrast, Duchenne dystrophy begins during early childhood and
causes fairly rapid weakness.
How is muscular dystrophy diagnosed?
Dr. Marks describes the different tests used to confirm that a child has the
disease. "In addition to a clinical history and a physical exam, we
perform a test that measures blood levels of serum creatine kinase, a muscle
enzyme that's released into the bloodstream when muscle fibers are
deteriorating in the body; elevated levels indicate that something is causing
muscle damage." If a child is found to have a high level of this enzyme,
the next test may be a DNA test or a muscle biopsy. The DNA test is used to
check for gene abnormalities, while the muscle biopsy is used to examine a
muscle tissue sample for patterns of muscle deterioration and abnormal levels
of dystrophin, a building block of muscle. These tests reveal the type of
muscular dystrophy the child has.
Caring for a child with Muscular Dystrophy
"Muscular dystrophy is a treatable but not curable disease, but we're
working on a cure," says Dr. Marks. "Kids are living longer and
having a better quality of life because we have new treatments." These
treatments improve muscle and joint function, slow muscle deterioration, and
keep kids comfortable, active, and independent for a longer period of time.
Many children with muscular dystrophy also develop weakened heart and
respiratory muscles. Dr. David Hammond, a neurologist at the Nemours Children's
Clinic in Jacksonville, FL, notes that because children can't cough out phlegm
due to weakened respiratory muscles, they sometimes develop respiratory
infections that can quickly become serious. Good general health care and
regular vaccinations are especially important for children with muscular
dystrophy to prevent these infections.
Many children eventually need devices to help them do simple things because
they become so weak. Anjali Weber, Director of Rehabilitation Engineering at
duPont, says that assistive technology devices can be customized to meet the
changing needs of children, making them much more independent, comfortable, and
active.
The search for a cure
Researchers are quickly discovering new information about muscular
dystrophy, information that helps doctors and other researchers better
understand its causes, patterns of development, and possible treatments. Both
Dr. Marks and Dr. Hammond agree that the most promising cure involves gene
therapy. In the case of Duchenne and Becker dystrophy, researchers are working
on ways to introduce normal dystrophin into a genetically engineered virus that
can then bind to afflicted muscle cells. Once bound to muscle cells,
researchers hope the virus can transfer its normal dystrophin gene to the
weakened muscles, enabling them to reproduce normal dystrophin and become
stronger.
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