tests are considered to be, and usually are, precise. However, as in any
other test, there are limitations in accuracy as specified below:
Therefore, in genetic screening tests:
- Molecular tests involve the use of biological substances (enzymes) intended for
research. According to the manufacturers of these substances, the level of precision
using them is about 99% rather than 100%.
- Genetic screening tests do not test for all possible errors (mutations) in the gene
responsible for a disease, only those that have been found to be common in the subjects
ethnic group. There may be other mutations for which analysis is available, but
since these are rare, this is not routinely done
- If no mutations are identified, the risk for having a child with the specific genetic
disease for which the test was performed is very low, but it still exists. This
risk depends on the carrier frequency in the subjects ethnic group, and also the
proportion of carriers that can be identified with the test performed the lower
the carrier frequency in your ethnic group or the greater the coverage of the test,
the lower the risk remaining after a negative test result for having an affected
infant. Information about carrier frequencies and the degree to which the mutations
checked cover the possibilities for a defect in a gene in your ethnic group can
be obtained at a genetic institute.
- If the subject has a relative with the disease that is being tested, it is important
to clarify which mutations (gene defects) are present in that relative. The genetic
institute that is carrying out the test on your genetic material (DNA) must ensure that the test also includes examination for
the mutation present in the patient in your family.