-Tissues tested include blood, skin, saliva and hair follicles and, prenatally, embryo, placental tissue and amniotic fluid; DNA can be tested using blood
-Genetic screening is done for a particular condition in individuals, groups or populations without family history of the condition
-Genetic testing is done for a particular condition where an individual is suspected of being at increased risk due to their family
history or the result of a genetic screening test
-Direct gene testing looks at the presence or absence of a known gene mutation by examining the sequence of letters in the information in the gene
-The test is very accurate and used for diagnosis and screening including prenatal, genetic carrier testing and screening, presymptomatic and predictive testing
Limitations include:
*Interpretation of the test result eg. finding that a person has a faulty gene does not always relate to how a person is, or will be, affected by that condition
*The testing may be time-consuming and expensive for the health service if not for the patient
*For some complex conditions eg. cancer, the testing may have to be done on a family member with the condition to identify a family-specific mutation in the gene (mutation searching) before unaffected family members can be offered predictive testing
-Indirect gene tracking (linkage) relies on comparing DNA markers from family members with the condition to markers in unaffected relatives
-Used in situations where the gene itself has not been precisely located or where mutation(s) in a gene have not yet been defined;
-the test is not as accurate as direct gene testing but can be used in diagnosis including prenatal and presymptomatic and predictive testing.
-It may not always be possible to find DNA markers that enable the scientists to tell the difference between the faulty gene copy and the working gene copy .
