Facioscapulohumeral muscular dystrophy (FSHD)
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Types and clinical signs
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This is one of the more common diseases in the group of muscular dystrophies, and
is second in frequency to
Duchenne muscular dystrophy.
The muscle weakness usually starts in the muscles of facial expression. The weakness
progresses and usually by adolescence the facial expression appears frozen, like
a mask, and the patient has difficulty in closing his eyelids and in moving his
lips while laughing. The disease also spreads to other parts of the body, mainly
the shoulders. The patient then has difficulty in lifting his shoulders and the
scapula (shoulder blade) becomes fixed. Sometimes the disease progresses more quickly
and sometimes more slowly. A precise diagnosis is important, and a diagnosis made
in the past is not always accurate by today's standards. Because of this, the diagnosis
must always be confirmed in a genetic institute by examining the patient, or at
least by reviewing the results of neurological tests, laboratory and/or EMG results,
and other data. Even though we know a lot about the inheritance patterns, the risk
of recurrence, pathogenesis, etc., most of these diseases have exceptions, and each
case/family must be examined individually in a genetic institute.
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Inheritance pattern
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Autosomal dominant inheritance.
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Penetrance
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The expression of the disease is usually full. There is great variation in the severity
of the disease; some patients have very few problems. In contrast, in others the
muscle weakness can be marked to the point of severe disability.
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Associated features that can be demonstrated in tests performed during pregnancy
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There are no specific signs in pregnancy.
In families in which the mutation that causes FSHD is present, a reliable genetic
test can be performed in the fetus if there is a high risk that he or she may be
affected.
The disease cannot be detected by
ultrasound examination in pregnancy.
It is important to bring to
genetic counseling all available data including the results of any additional
tests carried out during pregnancy such as alpha-fetoprotein, nuchal translucency, etc.
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What is the risk of recurrence in a subsequent pregnancy?
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Each patient has a 50% risk of having a child with the same condition. In a family
with FSHD, even asymptomatic individuals may develop the disease at a later age.
This means that healthy family members are also at risk of having affected children.
In families in which the characteristic gene for FSHD has been found, all the carriers
can be identified, even if signs of the disease have not yet appeared.
The exact risk for more distant relatives depends on the number of affected individuals
in the family, the relationship of each to the patients, consanguinity between the parents, if any, etc. The
risk is ascertained within genetic counseling.
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Molecular genetic information
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The gene for the disease and the location
of the gene
The mutation is a deletion in a relatively small segment at the end of chromosome
4, in a region known as 4Z4D. The characteristic of this region is that normally
there are multiple repeats of this segment - it is common to find regions that are
repeated a large number of times at the ends of the chromosomes. In FSHD, there
is a decrease in the number of repeats to less than 10 (normally there are 10 to
100 repeats). The deletion of a number of repeats can be demonstrated in FSHD using
molecular genetic methods.
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Genetic testing
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Diagnostic testing
When a patient presents with clinical FSHD, a direct test can be performed in order
to look for the common mutation that is present in most patients (the deletion of
the specific segment in chromosome 4). See: Testing the disease-causing
gene for mutations that are common in a specific ethnic group - autosomal dominant
diseases.
Carrier testing
The carriers are actually patients, even if they have not yet developed any signs
of the disease. In families in whom the specific mutation has been found, relatives
carrying the gene can be examined. Tests to identify carrier status in the healthy
population are currently not carried out.
Fetal testing
As for diagnostic testing.
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