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Skip Navigation LinksHome Page    >    Tests during the pregnancy    >    Indirect testing for genetic markers in a family that has a single patient – when there is only one gene that can cause the disease – autosomal dominant diseases
 
 
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Indirect testing for genetic markers in a family that has a single patient - when there is only one gene that can cause the disease - autosomal dominant diseases


This is not a direct test, but a comparative one. It is based on the fact that many patients with this inheritance pattern are the first ones in their family to be affected (a -new- mutation). Such individuals are known as probands. Usually in this situation the mutation is in the gene that has been transmitted to the affected child by his or her father. A DNA test of the patient-s parents along with that of the patient can determine which of the patient-s two genes is the one he inherited from his father (the paternal gene). This gene probably carries the mutation, and if transmitted to the patient-s offspring it will probably cause a similar disease (there is a varying confidence margin from disease to disease, reaching 95% in some cases).

So without identifying the mutation itself, prenatal diagnosis by amniocentesis or chorionic villus sampling can be performed in each pregnancy of the patient or the patient-s partner. The patient-s parents and partner must cooperate, as they must be examined by a physician in order to ascertain whether they have signs of the disease, and must agree to give a blood sample. The test is relatively simple and rapid compared to tests for reading the full sequence of the gene. Its reliability depends on the type of disease and on the likelihood that the new mutation has occurred in the paternal gene, and this is determined in genetic counseling.
 
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