DNA Tests

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KEY POINTS

• DNA tests check the genetic building blocks that tell your body how to develop and work.
• DNA tests may be used to check for disease or medical conditions caused by abnormal genes, to determine parents, or to help identify criminals or their victims.

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What is a DNA test?

A DNA test looks at the deoxyribonucleic acid (DNA) in your body’s cells. DNA is a long molecule that has 4 basic building blocks: adenine (A), cytosine (C), guanine (G) and thymine (T). The human body has about 3 billion of these building blocks. The order, or sequence, of these building blocks provides the information that tells your body how to develop and work.

Each DNA sequence of building blocks that contains instructions to make a protein is known as a gene. Genes are in each cell of your body, and are passed from parents to children. Humans have between 20,000 and 25,000 unique genes.

Because all cells in the body contain exactly the same DNA, samples can be taken from skin, hair, blood, and other body organs or fluids.

When is it used?

There are several uses for a DNA test:

• Diagnostic testing. DNA may be used in some cases to find the cause of symptoms. For example, DNA tests can detect many kinds of bacteria, viruses, or other causes of infections.
• Genetic disorder testing.

  Some problems, such as sickle cell anemia or Tay-Sachs disease, can be diagnosed before birth with DNA testing of a baby's cells. This is done by:

  • Chorionic villus sampling (CVS), which takes a small sample of tissue from the placenta (the tissue that carries oxygen and food from your blood to the baby’s blood). This test is usually done between the 10th and 13th weeks of pregnancy.
  • Amniocentesis, which uses a needle put through your belly to test the fluid that surrounds your baby. This test is usually done between the 15th and 18th weeks of pregnancy.

  Genetic testing can also be done on adults to check for changes in genes that increase your risk for certain diseases. For example, if you have inherited a change in BRCA1 and BRCA2 genes, it increases your risk for breast, ovarian, pancreatic, and prostate cancer.

• Medicine testing. The makeup of your genes can affect how certain medicines work. Knowing this can help your provider find which medicine will work best for you.
• Carrier testing. This tests family members who do not have a disease, but who are at risk for passing on a genetic disorder if they decide to have children.
• Family tree testing. This is a way to research your ancestors, the part of the world they came from, and your ethnic background.
• Parent testing. This can show if a child has genes that match a possible father (paternity), mother, or other close relatives.
• Crime scene investigation. Crime teams can test blood, sperm, hair, or saliva to identify suspects or their victims.

How do I prepare for a DNA test?

Usually no preparation is needed for this test.

Talk to your healthcare provider if you have any questions about the test. Based on why you are having the test, your healthcare provider may recommend that you see a genetics counselor. A certified genetics counselor is trained to help people understand the possible results of their genetic testing before they do it. The results may have psychological, family relationship, or financial effects.

How is the test done?

For a DNA test, you usually give a blood sample; DNA is then taken out of some of the white blood cells. For some DNA tests, you may have the inside of your cheek touched with a swab to gather the DNA. This type of specialized testing is done only by certain genetic testing laboratories. It takes a week or more for results to come back.

Tests of sperm or hair are usually done only to investigate crimes.

For more information, contact:

• The Genetic Alliance
  800-336-4363
  http://www.geneticalliance.org