Genetic Testing and Screening

Test Overview

A genetic test checks the DNA of your cells. It can find changes in your genes or chromosomes that may cause a genetic illness. The results may tell you about your ancestry, your health, or your risk for certain diseases.

Testing can be done on a single gene, selected genes, or all of your genes (your genome). The test can look for a single change in a gene or check the entire gene or chromosome for changes.

Genetic screening tests include prenatal screening and carrier screening. Prenatal screening checks your fetus for an increased risk for genetic conditions. Carrier screening shows if an adult carries a gene change that could be passed along to their child.

You inherit half of your genetics from each birth parent. Genes determine things like your blood type, hair color, and eye color. Genes can also affect your response to medicines.

What are the main types of genetic testing?

Genetic tests include:

• Carrier testing. This looks for gene changes that a person might pass along to their child.
• Prenatal screening and testing. This checks if a fetus is at risk for or has a condition like Down syndrome.
• Predictive testing. This is done to see if a person has a genetic change that increases their risk for developing a disease such as Huntington disease.
• Forensic testing. This is used to identify family members, crime suspects, and victims of crime, war, or disasters.
• Diagnostic testing. This may be used to confirm a specific genetic illness when a person has symptoms of a disease.
• Pharmacogenomic testing. This is done to see if a person has gene changes that might affect how their body reacts to a specific medicine.
• At-home genetic testing. This may offer information on ancestry, personal traits, lifestyle factors, and disease risks.

How can genetic counseling help?

The results of genetic testing can affect your life. Genetic counselors are trained to help you understand your risk of getting genetic diseases or having a child with an inherited disease, such as cystic fibrosis. It may be a good idea to get genetic counseling before deciding to have testing.

Genetic counseling may involve:

• Discussing what problems an inherited disease may cause.
• Teaching you and your partner about how a specific disease is inherited or passed from you to your child.
• Discussing whether and how to test for an inherited disease before you become pregnant or before your child is born.
• Discussing the likelihood that you and your partner will have a child with an inherited disease, based on test results.

Medical geneticists and genetic counselors are trained to help you and your family make informed decisions that are right for you. They are sensitive to physical and emotional aspects of these decisions. Your privacy and confidentiality are carefully protected.

Why It Is Done

Testing may be done to:

• Find out if you carry a changed (mutated) gene for an inherited disease, such as cystic fibrosis.
• Find out if your fetus is at risk for a genetic condition such as Down syndrome.
• Find out if you carry a changed gene that increases your risk for a disease later in life, such as breast cancer.
• Find out if you have an inherited heart disease called hypertrophic cardiomyopathy.
• Check for genetic changes that may affect your treatment for an existing disease.
• Find out if you have inherited gene changes that affect your response to medicines.
• Identify family members, crime suspects, or victims of war or disasters.

How It Is Done

Genetic testing can be done using almost any cell or tissue from the body. The type of sample needed will depend on the test.

Samples used in tests include:

• A blood sample from a vein. A health professional uses a needle to take a blood sample, usually from the arm.
• A cell sample from the cheek. A swab is used to scrape some tissue from the inside of the cheek.
• A saliva sample. The person being tested spits into a tube.
• A sample of amniotic fluid. This is collected using amniocentesis.
• A sample from the placenta. This is collected using chorionic villus sampling.

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How It Feels

Depending on the test, a sample of blood, saliva, amniotic fluid, or other tissue may be used.

• A blood sample from a vein may involve a quick sting or pinch from the needle.
• A saliva sample can be collected by having you spit into a tube. It isn't painful.
• A cheek swab collects cells from the inside lining of your cheek. It isn't painful.
• A sample of amniotic fluid is removed from your uterus (amniocentesis). You may feel a sharp sting for a few seconds when the needle is put in. As the fluid is taken out, you may feel some pulling or pressure in your belly. After the test, the area may be tender or sore for a few days.

Results

The results of genetic testing depend on the type of test done. For example, the results may show if you have a genetic condition or how likely it is that you will have one in the future. The results can also show if you are a carrier for a condition. The results of prenatal genetic screening may show how likely it is that your fetus will have a genetic condition.