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Patient education: Genetic testing (The Basics)

Patient education: Genetic testing (The Basics)

What is genetic testing? — Genetic testing is a way to find out information about your genes. This information can help you understand your risk for things like:

Certain diseases

Reactions to certain medicines

It can also help you make decisions about screening and treatment.

What do genes do? — Genes are made of DNA, which is inside most cells in the body. The genes are basically the body's recipe book. They tell your cells how to make different proteins, and they give instructions about how your body should work. For example:

Before you are born, your genes tell your body to make different organs.

After you are born, your genes tell your body how to work normally.

Your genes also determine things like your eye color.

Genes are organized onto chromosomes. Your complete set of genes is called your "genome." Everyone's genome is unique. That's why people's bodies all look and work differently.

Humans have about 20,000 to 30,000 different genes. You receive, or inherit, your genes from both of your parents.

What are genetic variants? — Differences in a person's DNA are called genetic "variants" or "mutations." These variants sometimes affect the way that your body makes proteins. This might or might not affect your health:

In some cases, variants can put you at risk for disease.

Sometimes, they might cause a small change that is neither better nor worse.

Sometimes, these changes do not have any effect at all. Or experts might not know enough about the change to understand how it will affect you.

How does genetic testing work? — Genetic tests can look at a person's genes and find variants that are linked to lots of different conditions.

There are several ways to do the testing. The differences include:

Number of genes tested – Some tests look at 1 gene. Some tests look at a group of genes. Some tests look at a person's entire genome (all of the genes).

Type of results given – Some tests look for specific gene changes that are related to a disease. In these cases, the results are reported as "positive" or "negative." A positive result means that you have the variant, and a negative result means that you don't. Other tests look at an entire gene or a group of genes to see if any of the genes have changes.

Sometimes, a test comes back with the result "variant of unknown significance." This means that it's not known if the change is related to a disease or might increase your risk of disease. In the future, it might be known after more research is done.

Type of sample used – All of the tests require DNA, which comes from cells in your body. Some tests use blood, and some use saliva (spit). Some use other fluids. For example, there are tests that look at samples of cells from the fetus (for a pregnant person) or at tumor cells (for a person with cancer).

Why do people get genetic testing? — People get genetic testing for different reasons:

Some pregnant people have genetic testing before their baby is born. This involves testing a sample that contains cells from the developing fetus. The sample can come from your blood or from your uterus. Doctors might recommend this testing if a disease runs in your family or if you have an ultrasound (imaging test) that shows problems with the fetus.

If you develop symptoms of a disease or get abnormal lab test results, your doctor might suggest genetic testing. This can help them figure out if you have the disease.

If you already have a disease, you might want to know if you have a genetic variant related to that disease. If you do have a certain variant, knowing this might affect your treatment options. Your family members can use this information to decide if they want to get tested, too.

If you have a family member who has a disease or tested positive for a genetic variant, you might want to know if you are also at higher risk. For example, hemochromatosis is a disorder that causes your body to take in too much iron. If 1 of your family members has the abnormal genes for this, you might choose to be tested.

You might want to find out if you are a "carrier" for a certain genetic variant to see if you could pass it on to your children. For some diseases, the baby has to inherit 2 copies of an abnormal gene to actually get the disease. Examples include cystic fibrosis and sickle cell anemia. If both parents are carriers, there is a chance that their children could inherit the gene from both parents and get the disease.

Can I buy my own genetic testing kit? — Yes. There are companies that sell at-home testing kits. These are also called "direct-to-consumer" tests. You can buy the kit, then follow the instructions and mail a sample of your saliva to a lab for testing. But your doctor might not be able to use the results from these kits, or they might need to repeat the test. If you think that you might have a disease gene, talk to your doctor directly.

Some companies test for variants in certain genes. Some only test for genes that tell about your ancestry, that is, what parts of the world your relatives came from. Different companies offer different tests, and it's not always possible to know how accurate they are. If you do want to try an at-home testing kit to look at how your genes might affect your health, or if you have already tried one, talk to your doctor about it.

How do I decide whether to get genetic testing? — Your doctor or a genetic counselor can help you make this decision. A genetic counselor is a person who knows about many genetic diseases and genetic testing. They can help you understand your options. They can also talk to you about what your test results might mean for you and your relatives.

Questions to think about include:

What you are hoping to learn from genetic testing

Your risk for certain diseases or conditions that run in your family

What costs might be involved in testing

What your test results might mean for you

What your test results might mean for your relatives

Your options for more testing or treatment based on the results

Lifestyle changes you can make to help lower your risk of disease

A doctor or genetic counselor can also help with some of these questions:

What genes are being tested, and what are the related diseases? – In most cases, genetic testing helps you understand if you are at a greater risk of having a disease. But it can't tell you for sure if you will get the disease. In most cases, only the most common genes for a disease are tested.

What do I plan to do with this information? – If you are planning to have children, it can be helpful to know whether you are a carrier for a genetic variant. A doctor or genetic counselor can explain the risk of your future children having the disease.

Sometimes, if you know that you have a genetic variant, you can do things to help lower your risk of getting a disease later in life. For example, you might be able to avoid alcohol or change other behaviors. It's usually not possible to completely prevent a disease.

If you already have a disease, the results might help you decide on the best treatment plan.

How will I feel if I get a positive result? – Testing positive for some genetic variants means that you might be at higher-than-average risk for a certain disease. It does not always mean that you have that disease or will get it later in life. Knowing that you have a genetic variant can be upsetting or stressful to some people, so some people prefer not to know this, especially if there's nothing they can do about it.

What does it mean if the result is negative? – A negative result does not mean that you will not get the disease. It only means that the gene the test looked at is normal. But most diseases can have other causes, including other genes or things in your environment.

Deciding to get genetic testing is not always easy. It's also not always clear what to do once you have the results. Your doctor or genetic counselor can help you talk through your feelings and worries.

What should I do about my genetic test results? — The most important thing is to discuss your results with your doctor or genetic counselor. They can help you understand what the results mean.

If you already have a disease, knowing that you have a specific variant might affect your treatment options. For example, some medicines used to treat cancer only work if the person has a certain genetic variant. Your doctor or genetic counselor can talk to you about your situation and your choices.

Where can I learn more? — Your doctor or genetic counselor can give you more information. You can also find information from the National Institutes of Health online:

What is genetic testing?

www.medlineplus.gov/genetics/understanding/testing/genetictesting

Genetic Testing FAQ

www.genome.gov/FAQ/Genetic-Testing

More on this topic

Patient education: Genetic testing for breast, ovarian, prostate, and pancreatic cancer (The Basics)
Patient education: Chorionic villus sampling (The Basics)
Patient education: Amniocentesis (The Basics)

Patient education: Genetic testing for hereditary breast, ovarian, prostate, and pancreatic cancer (Beyond the Basics)

This topic retrieved from UpToDate on: Feb 02, 2024.
Disclaimer: This generalized information is a limited summary of diagnosis, treatment, and/or medication information. It is not meant to be comprehensive and should be used as a tool to help the user understand and/or assess potential diagnostic and treatment options. It does NOT include all information about conditions, treatments, medications, side effects, or risks that may apply to a specific patient. It is not intended to be medical advice or a substitute for the medical advice, diagnosis, or treatment of a health care provider based on the health care provider's examination and assessment of a patient's specific and unique circumstances. Patients must speak with a health care provider for complete information about their health, medical questions, and treatment options, including any risks or benefits regarding use of medications. This information does not endorse any treatments or medications as safe, effective, or approved for treating a specific patient. UpToDate, Inc. and its affiliates disclaim any warranty or liability relating to this information or the use thereof. The use of this information is governed by the Terms of Use, available at https://www.wolterskluwer.com/en/know/clinical-effectiveness-terms. 2024© UpToDate, Inc. and its affiliates and/or licensors. All rights reserved.
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