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Williams syndrome
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Types
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This is a syndrome caused by a deletion of a small segment of the long arm of chromosome 7 (7q11) in the region
of a gene called elastin. Elastin is a component of connective tissue in the body
that supports the tissues, joints and bones. This deletion usually encompasses a
number of genes apart from elastin, and the more genes that are missing, the more
severe will be the clinical presentation.
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Clinical signs
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The syndrome may involve a number of systems, so the signs of the disease are not
always identical in different patients. The characteristic signs include:
- Heart defects,
especially aortic stenosis (narrowing of the main artery coming from the heart)
due to thickening of its wall. This is present in approximately 75% of cases.
- A very sociable personality, without fear of strangers.
- Characteristic facies - only experienced physicians can detect these changes because
they are very subtle and not particularly exceptional. The facies are attractive,
the nose structure small with the nostrils facing forwards, the lips full, and the
teeth relatively small with gaps between them.
- A significant percentage of cases have developmental delay. These children have
a good memory and high musical ability. However, they have difficulties with spatial
adjustment, difficulties in performing complex tasks such as complicated jigsaw
puzzles, delay in speech, and in some cases sleep disorders.
- Their voices tend to be hoarse.
- Some have an umbilical or inguinal (groin) hernia, are excessively supple, and have
soft, resilient skin.
- About 70% of these children have some delay in growth in the first four years of
life, with improvement thereafter. Some have a permanently slightly short stature.
- Laboratory tests indicate that these children may have high calcium levels in the
blood and/or urine.
- In about 20% of these children there are variations in the structure of the urinary
tract. Some have renal (kidney) artery stenosis (narrowing).
The diagnosis is usually confirmed by
FISH tests, using a specific fluorescent marker for the region containing
the elastin gene. In a regular chromosome test, the deletion in Williams syndrome
cannot usually be identified, especially in the amniocentesis chromosome test.
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Inheritance pattern
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Autosomal dominant.
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Penetrance
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Complete
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Associated features that can be demonstrated in tests performed during pregnancy
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The heart defect and kidney changes can be seen on ultrasound examination. However, it is rare
to diagnose this condition in a family that does not already have affected children.
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What is the risk of recurrence in a subsequent pregnancy?
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Affected individuals have a 50% risk in every pregnancy of transmitting the disease
to their offspring. Parents who have an affected child have a small risk (less than
1%) of having another affected child if they are healthy themselves, and the same
applies for other relatives such as siblings, uncles, etc.
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Molecular genetic information
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The genes for the disease
A number of genes next to the gene for elastin.
Location
The long arm of chromosome 7.
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Genetic testing
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Diagnostic testing
FISH test. Use of a specific fluorescent marker for the region of the elastin gene.
In a regular chromosome test, the deletion in Williams syndrome cannot usually be
identified, especially in the
amniocentesis chromosome test.
Carrier testing
There are no carriers, because the carriers are affected.
Fetal testing
As for diagnostic testing.
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