FAQ About Genetic Testing

National Human Genome Research Institute

National Institutes of Health
U.S. Department of Health and Human Services


Frequently Asked Questions About Genetic Testing



Genetic Testing: What It Means For Your Health and Your Family's Health
A brochure on genetic testing that explains the basics.

Overview

Genetic research is leading to the development of more genetic tests that can be used for the diagnosis of genetic conditions. Genetic testing is available for infants, children, and adults. Genetic tests can be used to diagnose a disease in an individual with symptoms and to help measure risk of developing a disease. Adults can undergo preconception testing before deciding to become pregnant, and prenatal testing can be performed during a pregnancy. Results of genetic tests can help physicians select appropriate treatments for their patients.

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What is genetic testing?

Genetic tests look for alterations in a person's genes or changes in the level or structure of key proteins coded for by specific genes. Genetic tests can also be used to look at levels of RNA that play a role in certain conditions. Abnormal results on these tests could mean that someone has a genetic disorder.

Types of genetic tests include:
What is a gene test?

Gene tests look for signs of a disease or disorder in DNA or RNA taken from a person's blood, other body fluids like saliva, or tissues. These tests can look for large changes, such as a gene that has a section missing or added, or small changes, such as a missing, added, or altered chemical base (subunit) within the DNA strand. Gene tests may also detect genes with too many copies, individual genes that are too active, genes that are turned off, or genes that are lost entirely.

Gene tests examine a person's DNA in a variety of ways. Some tests use DNA probes. A probe is a short string of DNA with base sequence complementary to (able to bind with) the sequence of an altered gene. These probes usually have fluorescent tags attached to them. During the test, a probe looks for its complement within a person's genome. If the altered gene is found, the complementary probe binds to it, and the fluorescent label can be used to identify the presence of the alteration.

Another type of gene test relies on DNA or RNA sequencing. This test directly compares the base-by-base sequence of DNA or RNA in a patient's sample to a normal version of the DNA or RNA sequence.

What is a chromosomal test?

Chromosomes are the large DNA-containing structures in the nucleus of a cell. Humans normally have 23 pairs of chromosomes: 22 pairs of autosomes (numbered 1 through 22) and 1 pair of sex chromosomes (either XX for females or XY for males). Chromosomal tests look at features of a person's chromosomes, including their structure, number and arrangement. These tests look for changes, such as pieces of a chromosome being deleted, expanded, or being switched to a different chromosomal location.

Types of chromosomal tests include:
What is a biochemical test?

Biochemical tests look at the amounts or activities of key proteins. Since genes contain the DNA code for making proteins, abnormal amounts or activities of proteins can signal genes that are not working normally. These types of tests are often used for newborn screening. For example, biochemical screening can detect infants who have metabolic conditions such as phenylketonuria (PKU). Because of a genetic defect, people with PKU lack the enzyme that breaks down a particular amino acid (protein building block) called phenylalanine. Consequently, phenylalanine builds up to higher than normal levels in the body, leading to a variety of health problems. If diagnosed early, PKU can be treated with a strict diet that is low in phenylalanine, avoiding foods that are high in protein or that contain certain artificial sweeteners.

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What information can genetic testing give?

Genetic testing can:
  1. Give a diagnosis if someone has symptoms.
  2. Show whether a person is a carrier for a genetic disease. Carriers have an altered gene, but will not get the disease. However, they can pass the altered gene on to their children.
  3. Help expectant parents know whether an unborn child will have a genetic condition. This is called prenatal testing.
  4. Screen newborn infants for abnormal or missing proteins that can cause disease. This is called newborn screening.
  5. Show whether a person has an inherited disposition to a certain disease before symptoms start.
  6. Determine the type or dose of a medicine that is best for a certain person. This is called pharmacogenetics.

People in families at high risk for a genetic disease have to live with uncertainty about their future and their children's future. A genetic test result that can show that a known alteration causing disease is not present in a person can provide a sense of relief.

A genetic test result showing that a person has a disease-causing gene alteration can also provide benefits. Such a test result might lead a person to take steps to lower his/her chance of developing a disease. For example, as the result of such a finding, someone could be screened earlier and more frequently for the disease and/or could make changes to health habits like diet and exercise. Such a genetic test result can lower a person's feelings of uncertainty, and this information can also help people to make informed choices about their future, such as whether to have a baby.

What are reasons to get different types of genetic tests?

Three diagnostic procedures are common in prenatal testing: ultrasound, amniocentesis, and chorionic villus sampling (CVS). Ultrasound uses the reflection of sound waves to create an overall picture of the developing fetus. Amniocentesis involves testing a sample of amniotic fluid from the womb surrounding the fetus. CVS involves taking a tiny sample of tissue from a region of the placenta that carries fetal cells rather than maternal cells.

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How do I decide whether to be tested?

People have many different reasons for being tested or not being tested. For many, it is important to know whether a disease can be prevented if a gene alteration causing a disease is found. For example, those who have inherited predispositions to breast or colon cancer have options such as earlier and more frequent disease screening or early treatment. Pharmacogenetic testing can indicate the best medicine or dose of a medicine for a certain person.

In other cases, there may be no treatment for the disease. For example are no preventive steps or cures for Huntington's disease (http://www.genome.gov/10001215), but test results might help a person make life decisions, such as career choice, family planning, or insurance coverage.

People can seek advice about genetic testing from a genetic counselor. Genetic counselors help individuals and families understand the scientific, emotional, and ethical factors surrounding the decision to have genetic testing and how to deal with the results of those tests. (See: Frequently Asked Questions about Genetic Counseling)

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What about direct-to-consumer genetic tests available on the Internet?

A variety of genetic tests are being offered directly to consumers, often over the Internet. Such direct-to-consumer (DTC) genetic testing usually involves the individual scraping a few cells from inside the cheek and mailing the sample to a laboratory that performs the test. If you are considering such genetic tests, it is a good idea to first discuss the issue with your health-care provider or a genetic counselor.

Here are some major types of direct-to-consumer genetic tests:

Also, your test results may show that you are at increased risk for a condition, such as Alzheimer's disease, for which there is currently no effective prevention or cure. Such knowledge may help you plan your life, but it may also make you and your loved ones anxious or depressed.

Finally, ask yourself if you are prepared to make changes in your lifestyle based on the test results. If you are not willing to take actions like stopping smoking or exercising more, such tests may not be of much benefit to you.

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Where can I find more information about genetic testing?

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Last Updated: March 11, 2014