Dna Testing

Definition of 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, sometimes called "innocent" changes, do not cause disease. 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. However, other reasons exist 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, thus providing enough DNA to test. In the laboratory, technicians look for changes in the DNA that cause the suspected disease, or 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 must not 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 cannot always prove that they are. If people have certain changes in their DNA that are not identical, they are not related. If the DNA molecules from two different people show the same series of innocent changes, the people are probably blood relatives.