An Overview of Whole Exome Sequencing (WES)
Whole exome sequencing (WES) is a process used to identify changes in your genes. This method is relatively new. As the technology advances, further research and more practical uses are expected to emerge.
Genetic testing is becoming very common. You can buy products that use hair or saliva samples to pinpoint certain genetic traits, and to learn which ethnic backgrounds are part of your ancestry. WES is a bit different because it is used to identify abnormalities in all of your genes. That’s true even if these changes were not previously linked to any disease. For example, it is not the right test to look for a specific gene change, such as the BRCA2 mutations identified in some cancers.
This article looks at how the WES works, and what role it may play in your overall health care.
How Genes Work
WES can be used to look for patterns to find the genetic cause of a medical disease. It helps to know some basics about genetics if you are thinking about using WES. Here are a few.
Your chromosomes are molecules that contain your genetic code. (You have 23 pairs of chromosomes—these are also called DNA molecules.) They are made up of long strands of nucleotide molecules. Your body reads these gene sequences in order to produce key proteins.
Genes and Genomes
All of your body’s traits are formed through the making of proteins that were coded by your genes. All of this genetic coding, for all of your 46 chromosomes, is called your genome
Exons
The parts of a DNA molecule that code for genes are called exons. They are mixed with introns, which are nucleotide sequences that do not code for traits. One gene may have several exons that code for more than one protein. Exons account for only 1% to 2% of your total DNA.
Each exon begins with a nucleotide sequence that signals a start to making protein, and ends with one that tells it to stop making proteins.
Exome
All of the exons in your entire set of chromosomes are referred to as the exome. WES, then, looks at your whole exome to identify changes that could be responsible for a disease or a health problem.
WES is quite thorough, and it looks at all of the genes in your body. Keep in mind, though, that it does not examine introns at all. Introns may have some effect on your body, but scientists do not yet fully understand this effect. It is not now thought to be as critical as the influence of exons.
Process
WES uses a blood sample to analyze your genes. Every cell in your body has a full copy of all 46 chromosomes, so blood cells work fine for this type of test.
WES testing uses a molecular technique called hybridization. It compares the nucleotide sequence of the sampled DNA with a standard or “normal” DNA sequence.
WES can pick up on mutations that are already known to cause disease. It can also detect changes in your genetic code that have not already been linked to a disease.
Where to Get Tested
There are many labs that run WES. If your healthcare provider wants this done, you might have your blood drawn at your practitioner’s office and the sample can be sent to a specialized lab for its reading.
You may decide to get the test without a healthcare provider’s order. If so, you can contact a lab that does WES testing directly and ask them for their instructions on how to do the testing.
Cost
It is important that you check the cost of testing. You should also check whether your health insurance will cover the cost of the test. Because WES is still relatively new, your insurance company may or may not cover the cost, depending on their policies.
If you are planning on paying for the test yourself, the cost can range between $400 and $1,500.
Considerations
If you or your child is going to have WES done, you need to be aware of the implications. There are a variety of things to consider before undergoing WES. They include privacy concerns, but also how you will handle what you now know about yourself. This is one area where you may wish to make a genetic counseling appointment, and have professionals discuss what the findings mean for you.
Genetic Counseling
As with other kinds of genetic tests, WES may deliver results that seem alarming or that are hard to understand. The field of genetics has grown so quickly that it feels hard to keep up, but there are professionals trained in genetic counseling to help you sort through such personal information.
Whether you’re concerned about cancer after some troubling test results, or you want to be sure about a pregnancy given your own family history, a genetic counselor can help explain why a test is needed. Many are trained in prenatal care, pediatrics, oncology, and other specific medical fields.
They are not doctors, at least in most cases. But they are a key part of your medical care, and ready to discuss the test results and what they might mean moving forward. Your healthcare provider may be able to connect you with one. You also can check with the National Society of Genetic Counselors through their online database to find one, or with a similar local or national group.