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


This is not a direct test, but a comparative one. The alleles (an allele is one member of the pair of genes at a given disease locus) that are common to patients are compared. The -shared allele- of the patients within the same family is the one in which the mutation responsible for the disease is located. So without identifying the mutation itself, additional family members can be tested, and prenatal testing by amniocentesis or chorionic villus sampling can be performed, by looking for the -shared allele- in the DNA among the affected individuals in the family.

This test is only reliable if DNA from the affected individuals in the family is already available, or if it can be obtained from a blood (or other) sample. In these cases it is possible to carry out the test if there is DNA from at least two affected individuals. The cooperation of the family members is required - 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 increases the larger the family is, and the more affected individuals there are in the family, but this indirect method always has a risk for errors of about 1% depending on the genetic counseling given.
 
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