What is Genomic Testing, Know Its Uses and Procedure, Differences Between Genomic and Genetic Testing

Genomic testing is a relatively new field of genetics. Genomic testing explores the ways in which your genes interact with each other and what these interactions mean for your overall health. Genomic testing is not the same as genetic testing. There are differences between the two fields, and genomic testing can show you how the body works on a molecular level. To know more about this new field of testing, here’s everything you need to know about genomic testing.

Genomic testing is the process of looking at the entire genome of an organism. This means that this testing is used to observe all the genes that make up an organism, such as the human body. A human being has over 25,000 different genes that comprise of over three billion DNA units. Genomic testing looks for any changes in these genes or any harmful alterations present anywhere in the genetic code.^{(1, 2, 3, 4)}

Genomic testing is used to diagnose, predict, prevent, and treat different genetic diseases and ensure the good health of people. Technological advances are the backbone of genomic testing as this has made it possible to integrate genomics into healthcare purposes, including screening and molecular diagnostics to detect mutations in genes. Over the years, the use of genomic testing in the healthcare industry has increased to include testing at the preimplantation stage, prenatal, neonatal, pediatric, adult, posthumous, and even preconception tests.^{(5, 6, 7)}

Today with the help of genomic testing, it is possible to determine your disease risk, disease progression, and even the possibility of recurrence.

Genomic testing is most commonly used for cancer treatment to find out how a tumor is most likely to progress and behave. This helps doctors determine how aggressive the cancer is going to be and how likely it is to spread or metastasize to other parts of the body.⁽⁸⁾

Most people often use the two terms, genomic and genetic, interchangeably. However, they are not the same. Genomic testing is different from genetic testing since it analyzes all the genes of a person. In contrast, genetic testing looks at only specific genes or a certain set of genes to identify a particular disease or mutation.^{(9, 10, 11)}

The similarity between the two types of testing is only that they are both linked with genes. However, the end result and applications are entirely different.

Let us look at some of the differences and similarities between genomic testing and genetic testing.

Genetics is the study of what impact genes have on a person. Genes are responsible for providing all the information to the body on how to manufacture various proteins that are ultimately responsible for determining the structure and function of every cell in the body. Sometimes, one mutation in a single gene can cause many different health conditions, such as muscular dystrophy, sickle cell disease, cystic fibrosis, Down’s syndrome, and many others. Another example is the BRCA1 and BRCA2 mutations that are known to cause ovarian and breast cancer.⁽¹²⁾

Genetic tests search for these genetic mutations that are inherited from parents and sometimes run in the family as well. Genetic testing can confirm a diagnosis, predict the future risk of a disease, and even identify if you are a carrier of a certain gene that may or may not cause diseases in your children.^{(13, 14)} To do this, genetic testing analyzes specific genes to determine the risk of hereditary or genetic diseases.

Meanwhile, genomics is the study of the structure, function, and mapping of the entire DNA, which includes all the genes of the body. This genetic material is known as the genome. Genomics helps analyze the function and structure of the genome. This is done in order to:

Understand how each biological system works individually and with each other.

Predict what issues can happen if these genetic interactions get altered or start to interfere with normal biological functions in the body.

Instead of identifying just one genetic pathway that has some fault or change, genomics looks at an entire host of genetic variables that are going to impact the treatment or development of a certain disease, such as diabetes or cancer. And unlike genetics, genomics is not limited to just looking at inheritable mutations. Genomics looks at how a person’s genetic makeup influences the course of any disease and how lifestyle, environment, and treatments can cause mutations that change the progression and course of the disease. By understanding these changes, doctors can make better and more informed choices with regard to treatment. The same has already been put into practice for conditions like autism spectrum disorder, cancer, and even chronic pain.^{(15, 16, 17, 18)}

So what can genomic testing be used for? Let’s take a look.

Genomic testing is used to identify which genetic mutations lead to the development of a disease and are responsible for the characteristics of that disease. This information helps doctors understand why some people go on to develop more aggressive forms of the same cancer as compared to others, why some people live longer with fatal diseases like HIV, or why some individuals just don’t respond to certain chemotherapy. Armed with this information, doctors, and drug makers are also able to develop more appropriate and targeted forms of treatment.^{(19, 20)}

Genetic tests are used to rule out or confirm a suspected genetic condition, especially one that runs in families, while genomic testing provides more in-depth data, including:

• It determines various risk markers to screen for diseases.
• It provides prognostic markers that help predict just how aggressively a disease will progress, how likely it is to recur, and what will be the eventual outcome of the disease.
• It gives you predictive markers that help guide the exact treatment options and also avoids drug toxicity and unnecessary side effects of taking the wrong medicine that won’t help your condition.
• It provides response markers to find out just how effective some treatments will be.

Genomics is seen as being the foundation for a future where personalized medicine is a reality. Instead of following a one size fits all approach, personalized medicine based on your genomic makeup will offer a customized treatment for each disease.^{(21, 22)}

Genomic testing is usually part of a panel of targeted gene tests that either look for genetic hot spots that are known sites of mutation or complete gene sequencing. The test is performed in special laboratories that are certified by the government.

Most genomic tests require a sample of your blood or saliva or a buccal smear in which a swab is taken from the inside of your cheek. Depending on the exact purpose of the test, it might only need a few drops of blood, or it may need a couple of vials. For people with cancer, a biopsy of the bone marrow or tumor might also be required. Once the sample is obtained, it takes around one to four weeks to get the results.

Before you give the test, a genetic counselor will explain all the limitations of genomic testing, how it will be done, and what the results may or may not mean.

Genomic testing is primarily done through next-generation sequencing. Next-generation sequencing first finds and evaluates the genetic sequence of the many short DNA segments that are known as reads. There are millions of reads in the body. These reads are then put together into a whole sequence to find out which genetic variants are there and what they indicate. Next-generation sequencing is a very flexible procedure, and it can be used to sequence only a couple of genes or the entire genome that is usually used for research purposes or to screen for rare diseases. A hereditary breast cancer panel is an example of how next-generation sequencing can be used for sequencing just a few genes for specific diseases.^{(23, 24, 25)}

Most genetic variants, though, have very little or even no impact on our health. This is why these are filtered out during next-generation sequencing, and the few that are medically significant are identified and filtered out. These filtered variants are then scored against a five-point scale that is as follows:

• Benign or not causing any disease
• Likely to be benign
• Uncertain status
• Likely to be pathogenic or disease-causing
• Definitely pathogenic

Most laboratories report only the pathogenic and likely to be pathogenic findings. The test report also includes a detailed interpretation of the results by a professional geneticist.

Genomic testing is an important part of the treatment and management of various types of cancer. Genomic testing helps find the genetic markers that are typically associated with the disease and can help predict how the tumor will behave, how fast it will grow, and how likely it is that the cancer will metastasize or spread to other parts of the body.⁽²⁶⁾

It is essential to know this information since cancer cells tend to mutate rapidly and also spread equally rapidly. A genomic test tells your oncologist the most effective ways of treating that particular cancer. For example, if a tumor suddenly mutates, undergoing a genomic test can tell your doctor if that mutation can be treated effectively with targeted therapy.⁽²⁷⁾

While most genomic testing is carried out in hospital settings, there are home genomic tests available as well that help trace down a person’s ancestry. Some websites even offer customers the option to undergo genomic testing to identify the risk of numerous genetic disorders and if there is a predisposition to that condition. Genomic testing can help provide doctors and patients with a much better understanding of diseases as well as the best way to treat them. To find out if you are at risk for any disease, you can always undergo a genomic test after consulting your doctor.

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