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Special cytogenetic tests
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In these tests, small deletions and duplications at certain sites in a gene or chromosome
may be identified.
These deletions and duplications cannot be identified using a classic cytogenetic (chromosome)
test routinely performed on the amniotic fluid or chorionic villi.
In addition, these tests are necessary to complement regular cytogenetic tests in cases where
a structural change has been identified in one or more chromosomes.
In some cases, the position of the duplication or deletion in the chromosome can be located
using these tests.
By means of these tests, abnormalities in the number of chromosomes (e.g. Down syndrome)
can be detected in the amniotic fluid without culturing cells.
This means that an initial result can be obtained two days after the amniocentesis has
been performed.
This is a significant advantage, especially in pregnancies in which a problem arousing suspicion
for Down syndrome has been identified in the fetus in advanced weeks (see Amniocentesis:
"Additional amniotic fluid tests").
Also, there are a number of well-known genetic syndromes, such as
Prader Willi syndrome, that are caused by small chromosomal deletions.
These conditions can only be identified using this test.
Testing for these syndromes is performed in cases where there is a family history of a similar
problem or where the findings of the ultrasound scan have indicated that there may be a problem
such as a heart defect in the fetus.
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