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DNA testing

DNA testing is a type of genetic test that looks for changes in the DNA molecule. The changes, called mutations, may be associated with genetic diseases. Diseases such as the inborn errors of metabolism are diagnosed this way. The changes may also be variations in the DNA molecule that occur between the genes. These changes don't cause disease, and are sometimes called innocent changes. Identifying them can be useful for such things as paternity testing.

Who is a candidate for the test? 
People with genetic diseases are candidates for DNA testing. For DNA testing to be useful, the mutation that causes the disease must be known. People with a family history of a genetic disease are also candidates for DNA testing. In these cases, the change in the DNA of the affected relative must be known for DNA testing to be useful. People who want to prove blood relationship with someone else may want DNA testing. This identity testing usually involves disputed paternity. But there are other reasons for wanting to know about blood relationships. The innocent variations between the genes on the DNA molecule are checked in identity testing.

DNA testing can be done before birth using amniocentesis. It also can be done after birth, or even after someone has died.

How is the test performed? 
DNA can be collected from many types of cells. Cells from blood, tissue biopsy, hair, bone and skin scrapings are commonly used in DNA testing. If the specimen contains enough DNA for testing, no special work has to be done to get more DNA. If the sample is small, the amount of DNA must be increased. This is done with a technique known as polymerase chain reaction (PCR). PCR accurately copies the original DNA molecule many times, giving enough DNA to test. In the laboratory, technicians look for changes in the DNA that cause the suspected disease. Or they look for innocent changes that can be used to determine blood relationship.

What is involved in preparation for the test? 
No special preparation is needed for most DNA testing. If the sample will be collected by biopsy, special care must be taken to ensure a sterile specimen. If the sample will be collected from blood cells, the person cannot have had a recent blood transfusion.

What do the test results mean? 
DNA testing is quite specific. For diagnosis, the testing is accurate. Someone who has a change in DNA that is known to cause genetic disease either has the disease already, or will develop the disease in the future.

Identity testing can prove that people are not related. But it doesn't always prove that they are. If people have key changes in their DNA that are not identical, they are not related. If enough innocent changes in the DNA molecules from different people are identical, the people are probably blood relatives.

Reviewer: HealthAnswers Australia Medical Review Panel
Editor: Dr David Taylor, Chief Medical Officer HealthAnswers Australia
Last Updated: 1/10/2001
Potential conflict of interest information for reviewers available on request

This website and article is not a substitute for independent professional advice. Nothing contained in this website is intended to be used as medical advice and it is not intended to be used to diagnose, treat, cure or prevent any disease, nor should it be used for therapeutic purposes or as a substitute for your own health professional's advice.  All Health and any associated parties do not accept any liability for any injury, loss or damage incurred by use of or reliance on the information.


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