Defect in the closure of the abdominal wall Omphalocele and gastroschisis
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Omphalocele
(Intestines herniating through the umbilical orifice).
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Clinical signs
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This is a defect in the abdominal wall manifesting in the herniation of some of
the intestines and possibly other organs too outside the abdominal wall. They protrude
through the umbilicus (navel), through a ring that surrounds the umbilical cord.
The intestines and organs inside the herniated sac in the umbilicus are not covered
by skin, only by a transparent membrane. The size of the sac depends on the how
extensive the herniation is. Surgical intervention is undertaken immediately after
birth and usually has a 50% - 60% success rate. The unsuccessful cases are usually
those that are very extensive or accompanied by other defects.
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Complications
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The intestines outside the abdominal wall are susceptible to infection, dehydration,
trauma, or impaired blood flow.
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Frequency
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1 in every 4,000 births.
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Associated defects
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These occur in 66% of cases of omphalocele.
The typical defects are
heart defects, and defects of the urogenital system and nervous system.
There are also specific syndromes associated with omphalocele, including Beckwith
Weidemann syndrome, where the patients have a large tongue and a relatively large
body in addition to omphalocele, and
Down syndrome.
It is important to test for Beckwith Weidemann syndrome, because early diagnosis
soon after birth and appropriate intervention can prevent hypoglycemia (low blood
sugar level), which is common in these patients after birth.
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Hypoglycemia occurring immediately after birth can result in brain damage and mental
retardation, although the hypoglycemia resolves later.
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Inheritance pattern
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Unknown - in a small number of families, autosomal dominant and X-linked inheritance have been found.
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Penetrance
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Unknown.
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Risk of recurrence
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Not known with certainty.
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Associated features that can be demonstrated in tests performed during pregnancy
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On ultrasound examination,
signs of intestinal blockage must be looked for and the size of the defect assessed.
Associated defects must be looked for (see above).
Amniocentesis
should be considered because of the relatively high risk of chromosome disorders that are associated with
this defect. In all these cases it is important to refer the couple for genetic
counseling, to which they should bring all available data, including the results
of other tests performed during the pregnancy such as alpha-fetoprotein, nuchal translucency, etc.
It is advisable to refer the parents to a multidisciplinary clinic in a hospital
for professional counseling by a geneticist, an expert in ultrasound examinations,
a pediatric surgeon, and a neonatologist, in order to collate all the data and discuss
the various risks in each specific case, the method of monitoring the fetus, possible
intervention if indicated, etc. The decisions taken will depend on the severity
of the problem, the presence of additional findings, etc.
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Molecular genetic information
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The gene for the disease
No specific gene for omphalocele is known. In Beckwith Weidemann syndrome a number
of genes responsible for the syndrome have been identified.
Location
In Beckwith Weidemann syndrome, the genes responsible are situated on chromosome
11.
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Genetic testing
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Diagnostic testing
There is no genetic test for diagnosing omphalocele. A number of genes associated
with Beckwith Weidemann syndrome have been identified. Only in a very small number
of cases of this condition is it possible to identify the genetic mutation. In a
small percentage of cases, it is possible to demonstrate in chromosome testing on
blood or amniotic fluid an insertion (duplication) of a small segment in chromosome
11. In another small percentage of cases of Beckwith Weidemann syndrome, the mutation
has been identified as an asymmetric transfer of genetic information in chromosome
11. In these cases both chromosomes 11 originate from the father rather than one
originating from each parent - a condition called uniparental disomy. In the great
majority of cases, however, it is difficult to identify the precise mutation, even
though the gene in question is known to be situated on chromosome 11. This is a
test performed in research laboratories, and it is carried out on an individual
basis. The test takes such a long time that it cannot be completed during the course
of a pregnancy, and it is not routinely performed apart from in special cases via
genetic institutes.
Carrier testing
There are no tests for carrier status of omphalocele.
Fetal testing
There are no genetic tests for diagnosing omphalocele in the fetus.
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Gastroschisis
(intestines protruding through the abdominal wall)
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Clinical signs
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This is a defect in the abdominal wall through which the intestinal loops protrude.
The loops are free, appear thickened (edematous) and are not covered with a membrane.
The umbilical cord is not involved and enters the abdominal wall, usually on the
left of the defect. Infants with this defect usually have a low birth weight.
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Complications
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The organs (usually intestines) that are outside the abdomen are susceptible to
infection, dehydration, trauma or impaired blood flow. In addition, the intestines
may twist around their axis, a condition called volvulus. This may lead to necrosis
(death) of the intestine or obstruction of the flow of food.
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Associated defects
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There are usually no associated defects, and the problem is to repair the existing
one. If the defect is large, the repair is often difficult and is carried out in
stages. The causes of gastroschisis are probably not genetic. The defect in the
abdominal wall characteristic of gastroschisis may be caused by impaired blood flow
to this region of the abdominal wall during intrauterine life.
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Frequency
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1 in 6,000 births.
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Inheritance pattern
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The defect is not considered hereditary.
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Risk of recurrence
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There is no precise information, but it is usually not high.
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Associated features that can be demonstrated in tests performed during pregnancy
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On ultrasound examination, signs of intestinal blockage must be looked for and the
size of the defect that has to be repaired must be assessed. It is important to
ascertain that there is no omphalocele. In all cases, it is important to refer the
couple for genetic counseling,
to which they should bring all available data, including the results of other tests
performed during the pregnancy such as alpha-fetoprotein, nuchal translucency, etc.
It is advisable to refer the parents to a multidisciplinary clinic in a hospital
for professional counseling by a geneticist, an expert in ultrasound examinations,
a pediatric surgeon, a plastic surgeon, and a neonatologist, in order to collate
all the data and discuss the various risks in each specific case, the method of
monitoring the fetus, possible intervention if indicated, etc. The decisions taken
will depend on the severity of the problem, the presence of additional findings,
etc.
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Molecular genetic information
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The gene for the disease
No specific gene for gastroschisis is known
Location
No gene is known.
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Genetic testing
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Diagnostic testing
There is no such test for gastroschisis
Carrier testing
There is no such test for gastroschisis
Fetal testing
There is no genetic test for gastroschisis
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