Genetic Testing
What is Genetic Testing?
Genetic testing looks for changes, sometimes called mutations or variants, in your DNA. Genetic testing is useful in many areas of medicine and can change 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 or information about your risk to develop cancer. There are many different kinds of genetic tests. Genetic tests are done using a blood or spit sample and results are usually ready in a few weeks. Because we share DNA with our family members, if you are found to have a genetic change, your family members may have the same change. Genetic counseling before and after genetic testing can help make sure that you are the right person in your family to get a genetic test, you’re getting the right genetic test, and that you understand your results.
Reasons for Genetic Testing
- To learn whether you have a genetic condition that runs in your family before you have symptoms
- To learn about the chance a current or future pregnancy will have 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 might decide it’s not right for you. Some reasons might be that it’s not relevant to you or won’t change your medical care, it’s too expensive, and the results may make you worried or anxious.
Types of Genetic Tests
There are many different kinds of genetic tests. There is no single genetic test that can detect all genetic conditions. The approach to genetic testing is individualized based on your medical history and what condition you’re being tested for
Single gene testing. Single gene tests look for changes in only one gene. Single gene testing is done when your doctor believes you or your child have symptoms of a specific condition or syndrome. Some examples of this are Duchene muscular dystrophy or sickle cell disease. Single gene testing is also used when there is a known genetic mutation in a family.
Panel testing. A panel genetic test looks for changes in many genes in one test. Genetic testing panels are usually grouped in categories based on different kinds of medical concerns. Some examples of genetic panel tests are low muscle tone, short stature, or epilepsy. Panel genetic tests can also be grouped into genes that are all associated with higher risk of developing certain kinds of cancer, like breast or colorectal (colon) cancer.
Large-scale genetic or genomic testing. There are two different kinds of large-scale genetic tests..
- Exome sequencing looks at all the genes in the DNA (whole exome) or just the genes that are related to medical conditions (clinical exome).
- Genome sequencing is the largest genetic test and looks at all of a person’s DNA, not just the genes.
Exome and genome sequencing are ordered by doctors for people with complex medical histories. Large-scale genomic testing is also used in research to learn more about the genetic causes of conditions. Large-scale genetic tests can have findings unrelated to why the test was ordered in the first place (secondary findings). Examples of secondary findings are genes associated with a predisposition to cancer or rare heart conditions when you were looking for a genetic diagnosis to explain the symptoms of a complex disease.
Testing for Changes Other than Gene Changes
- Chromosomes. DNA is packaged into structures called chromosomes. Some tests look for changes in chromosomes rather than gene changes. Examples of these tests are karyotype and chromosomal microarrays.
- 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 be used to guide chemotherapy treatment for breast cancer.
Types of Genetic Test Results
- Positive – the test found a genetic change known to cause disease.
- Negative – the test did not find a genetic change known to cause disease. Sometimes a negative result occurs when the wrong test was ordered or there isn’t a genetic cause for that person’s symptoms. A “true negative” is when there is a known genetic change in the family and the person tested did not inherit it. If your test results are negative and there is no known genetic change in your family, a negative test result may not give you a definite answer. This is because you might not have been tested for the genetic change that runs in your family.
- Uncertain – a variant of unknown or uncertain significance means there isn’t enough information about that genetic change to determine whether it is benign (normal) or pathogenic (disease causing).
A good way to think about genetic testing is as if you’re asking the DNA a question. Sometimes we don’t find an answer because we weren’t asking the right question or science just didn’t have the answer yet.
Next Steps
If you have a family history of a genetic condition, have symptoms of a genetic condition, or are interesting in learning about your chance of having a genetic condition, talk to your doctor about whether genetic testing is right for you.
Additional Resources
- Find a genetic counselor in your area through the National Society of Genetic Counselors
- Find a medical geneticist (genetic doctor) in your area through the American College of Medical Genetics and Genomics
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