Patient education: Genetic testing (The Basics)

What is genetic testing? — 

This is a way to find out information about your genes. This information can help you understand your risk for things like:

●Certain diseases

●How your body handles certain medicines

It can also help you decide about testing and treatment for some conditions.

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 that are different in different people, like eye color.

Genes are organized onto chromosomes. Your complete set of chromosomes is called your "karyotype." 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 sometimes affect how your body makes proteins. This might or might not affect your health:

●In some cases, genetic variants can put you at risk for disease. These are called "pathogenic variants."

●Sometimes, they might cause a small change that does not put you at risk for disease.

●Sometimes, genetic variants have not been studied enough to know how they will affect you.

How does genetic testing work? — 

The 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, while others look at a group of genes. Some look at a person's entire genome (all the genes). A karyotype looks at the number of chromosomes rather than individual 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 you have the variant, and a negative result means you don't. Other tests look at an entire gene or a group of genes to see if any have changes.

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

●Type of sample used – All the tests require DNA, which comes from cells in your body. Some tests use blood or saliva (spit). Others use different kinds of samples. 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, it might affect your treatment options. Your relatives can use this information to decide if they want to get tested, too.

●If you have a relative 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 the body to take in too much iron. If 1 of your relatives has the genetic variant for this, you might choose to be tested, too.

●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 their children could inherit the genetic variant 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 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, meaning 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.

Should I get genetic testing? — 

Your doctor or a genetic counselor can help you decide. 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 will I do with this information? – If you are planning to have children, it can help 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 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.

●How will I feel if I get a positive result? – Testing positive for some genetic variants means you might be at higher-than-average risk for a certain disease. It does not always mean you have that disease or will get it later in life. Knowing you have a genetic variant can be upsetting or stressful, 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 you will not get the disease. It only means the gene (or part of 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 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

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