General information
Other names
| Where It's Done | Who Does It | How Long It Takes | Discomfort/Pain |
| Doctor's office, hospital, or commercial laboratory. | Doctor, nurse, or lab technician. | Less than 5 minutes. | Slight (from drawing blood or obtaining tissue sample). |
| Results Ready When | Special Equipment | Risks/Complications | Average Cost |
| 2-4 weeks. | Supplies for drawing blood or a or cheek brush (for removing cheek cells); rarely, a biopsy tool. | Almost negligible risk associated with obtaining tissue cells. | $-$$ |
None.
Purpose- To detect genes that may cause or increase the risk of disease later in life or be passed on to offspring.
- To detect a severe genetic disorder in a fetus when there is a family history of it.
DNA "markers" linked to the problem genes are identified in your chromosomes and those of your close relatives.
PreparationNone.
Test procedure- Blood is usually drawn (although other tissue samples may be taken) from the patient and several of his or her relatives.
- The DNA of affected and unaffected relatives is extracted and analyzed to determine which DNA structures are most likely to represent markers of the disease-causing gene.
- The patient's DNA is examined for the presence of the markers.
If blood has been taken, follow the normal procedure for drawing blood. Otherwise, the care you receive depends on the procedure used to obtain a tissue sample.
Factors affecting results- Correctly identifying how people in a particular family are related to each other is crucial to accurate results.
- The test will have limited value if close relatives crucial to establishing linkage relationships are not available.
- Occasionally, DNA segments may have changed places when the subjects' eggs and sperm were formed, causing the markers to move from their usual locations.
- The presence of DNA markers can help predict whether a fetus or a person with no symptoms carries the defective genes that run in the family.
- If the markers are not found, the presence of abnormal genes cannot be ruled out because DNA structures in the vicinity of the gene may have been rearranged when inherited.
- A small number of disorders have gene markers that are found in most people with the disease (and in few people without the disease), but in most cases the markers are specific to a particular family, and will differ from family to family.
- In an experimental approach with limited availability, results can be used to make cancer treatment decisions or take preventive measures.
The test makes it possible to diagnose genetic abnormalities when the gene causing the disorder has not yet been identified.
Disadvantages- It's expensive.
- It's available in only a few medical centers and for a limited number of disorders.
- Close relatives must be available for testing.
- It's laborious, more time-consuming, and less reliable than direct gene analysis.
Both positive (abnormal gene present) and negative (abnormal gene not present) findings are considered highly informative. Either result may lead to further counseling, treatment, and, if appropriate, reproductive decisions. Direct gene analysis may be suggested in the future if it becomes available for the gene in question.
