Muscular dystrophy
(MD)
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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.
Nine major types of muscular dystrophy occur. The
most common muscular dystrophies appear to be due to
a genetic deficiency of the muscle protein
dystrophin.
There's no cure, but medications
and therapy can slow the course of the disease.
Causes
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 gene.
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.
When to seek medical advice
Duchenne's muscular dystrophy occurs almost exclusively in boys,
although it can occur in girls. Your young child may have difficulty
walking, running, getting up or climbing the stairs, or may appear
clumsy and fall often. These may be early indications of muscular
dystrophy. A child with MD may learn to walk later than other children
do and may exhibit signs of muscle weakness between the ages of 2 and 5.
By school age, a child with MD may walk unsteadily and on the toes or
balls of his feet. Duchenne's MD usually results in children losing the
ability to walk between the ages of 7 and 12.
If you're concerned about your child's motor abilities, clumsiness or
muscle strength and development, see your doctor. Once muscular
dystrophy is diagnosed, medications and physical therapy can help slow
its progression.
Because muscular dystrophies are inherited disorders, genetic counseling
may be helpful if you're considering having children and to assess the
risk of the disease in other family members.
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