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How is a molecular genetic test performed?
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These tests examine the DNA sequence in a gene in order to determine whether or not a mutation is present. In the future, it may be possible
to read the entire genetic sequence rapidly, effectively and cheaply. At present,
however, the test is slow and labor-intensive (there are hundreds of letters that
must be read for each gene), time-consuming and expensive.
These tests are therefore performed in situations where one or both partners (depending
on the inheritance pattern of the disease concerned) are at high risk for a condition
involving a specific gene.
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For example, if a family has a relative with a certain type of muscular dystrophy,
such as Duchenne,
and the gene is already known, a mutation in the gene responsible for the disease
is initially sought.
Only after a mutation has been identified are additional family members tested in
an order directed by the geneticist (according to heredity, etc.).
If the risk is also high for the fetus (because the mother is a carrier), the fetal
DNA is tested. Without the knowledge of the disease and the specific mutation in
the patient, it would not be possible to examine the fetus.
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Today, these tests are mainly performed in the following cases:
- In families with a history of a genetic disease that can be identified using DNA
methods.
- For the identification of carriers of diseases for which screening is available.
If both parents are carriers for a disease that may be expressed in their fetus,
the fetus can also be tested using these methods.
These screening tests are currently performed as a service for the population both
before and during pregnancy. A large proportion of the tests are carried out in
genetic institutes and private laboratories through geneticists, but in exceptional
cases, the sample is sent abroad to be tested. The tests are performed on peripheral
blood (taken from a vein) or fetal cells (usually from amniotic fluid or chorionic villi). The hereditary material (DNA)
is extracted from the white blood cells, and the tests are carried out using various
methods.
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