Medicine

Genetic Testing

This post originally appeared on MedLine Plus.

What it is

Genetic testing looks for genetic changes, sometimes called mutations or variants, in your DNA. Some genetic changes can cause disease or other health conditions. You inherit your DNA from your parents, so any genetic changes they have can be passed down to you.

Genetic testing can give you information to help guide the decisions you make about the medical care you or your family member receives. For example, genetic testing can provide a diagnosis for a genetic condition such as fragile X syndrome or information about your risk of developing cancer. There are many different kinds of genetic tests. Genetic tests use a blood or spit sample, and results are usually ready in a few weeks.

Because we share DNA with our family members, if testing shows that you have a genetic change, your family members may have the same genetic change. Genetic counseling before genetic testing can help make sure you are the right person in your family to get a genetic test and can help make sure you’re getting the right test. Genetic counseling after genetic testing can help make sure you understand your results.

Reasons for genetic testing

There are several reasons to consider getting a genetic test, including the following:

  • To learn whether you have a genetic condition that runs in your family, before you have symptoms
  • To learn whether you could have a child with a genetic condition
  • To diagnose a genetic condition if you or your child has symptoms
  • To understand and guide your cancer prevention or treatment plan

After learning more about genetic testing, you can decide if it’s right for you.

Types of genetic tests

There are many different kinds of genetic tests. There is no single genetic test that can detect all genetic conditions. Your healthcare provider can help you decide what genetic test is right for you based on your medical and family history and the condition for which you’re being tested.

Single gene testing

Single gene tests look for genetic changes in only one gene. Your healthcare provider might recommend single gene testing if you or your child have symptoms of a specific condition or syndrome that is usually or always caused by changes in the same gene. Examples include Duchenne muscular dystrophy and sickle cell disease. If there is a known genetic change (mutation) in your family, your healthcare provider might recommend single gene testing to check for that change.

Genetic testing panels

Genetic testing panels look for genetic changes in many genes in the same test. Your healthcare provider might recommend a genetic testing panel if you or your child have symptoms of a disease or condition that can be caused by genetic changes in many different genes. Examples include primary immunodeficiency, cerebral palsy, and epilepsy. Your healthcare provider might also recommend a genetic testing panel to check for genetic changes that make you more likely to develop a disease such as breast cancer or colorectal (colon) cancer, especially if the disease runs in your family but a specific genetic change that might be causing the disease in family members has not yet been identified.

Large-scale genomic testing

There are two different kinds of large-scale genomic tests, which look for genetic changes throughout a person’s DNA:

  • Exome sequencing looks at all the genes in the DNA (whole exome) or just the genes that are related to medical conditions (clinical exome).
  • Whole genome sequencing is the largest genetic test and looks at all of a person’s DNA, not just the genes.

Your healthcare provider might recommend exome sequencing or whole genome sequencing if you or your child has a complex medical condition, or if other testing has not found a genetic cause for a disease or condition. For example, your healthcare provider might recommend whole genome sequencing if you have a rare disorder that appears to have a genetic cause, but none has been found using other tests.12 If your child has autism spectrum disorder, your healthcare provider might recommend whole exome sequencing if other testing does not find a cause.3

Large-scale genetic tests can have findings unrelated to why the test was ordered in the first place. These are called secondary findings, and they can include genetic changes related to adult-onset conditions in children. For example, a child may have exome or genome sequencing to provide a genetic diagnosis for autism spectrum disorder, and a secondary finding is that they have a genetic change that makes them more likely to develop breast cancer as an adult.

Clinical versus direct-to-consumer genetic tests‎

Clinical genetic tests are different from direct-to-consumer (DTC) genetic tests. Your healthcare provider orders clinical genetic tests for a specific medical reason—you cannot order them on your own. In contrast, you can buy DTC tests online or in a store, for example, to learn more about your ancestry. DTC test results can be used to make decisions about lifestyle choices or identify issues to discuss with your healthcare provider. However, DTC tests cannot determine for certain whether or not you will get a disease. Nor should these tests be used alone to make decisions about your treatment or medical care or in place of clinical genetic testing.

Other tests

Some tests check for changes other than gene changes.

Chromosomes

DNA is packaged into structures called chromosomes. Some tests look for changes in chromosomes rather than in genes. For example, your healthcare provider might recommend a type of chromosome testing called a chromosomal microarray if your child has autism spectrum disorder.

Gene expression

Genes are expressed, or turned on, at different levels in different types of cells. Gene expression tests compare these levels between normal cells and diseased cells, because knowing about the difference can provide important information for treating the disease. For example, these tests can guide chemotherapy treatment for breast cancer.

Understanding test results

Genetic counseling is important to help you understand what the results of your test mean for you. What results mean for you can depend on your family health history, age, and other factors.

This post originally appeared on MedLine Plus.