A gene is a segment of DNA that provides the cell with instructions for making a specific protein, which then carries out a particular function in your body. More than 99.9% of your DNA sequence is identical to any other human. Still, we are different. Some of these differences are enough to change the shape and function of a protein, how much protein is made, when it’s made, or where it’s made. More importantly, variations in your genome also influence your risk of developing diseases and your responses to medications.

Genome is the word used to describe all your DNA. All living organisms have their own genome, and each genome contains the information needed to build and maintain that organism throughout its life. Your genome is the operating manual containing all the instructions that helped you develop from a single cell into the person you are today.

A genetic disease is caused by certain changes (also called mutations or variants) in the DNA sequence. Some diseases are caused by changes that may be inherited from the parents or may occur de novo during early development and are present in an individual at birth. Other diseases are caused by changes in a gene or group of genes that occur during a person’s life. Most changes in DNA are not expected to cause disease.

Genetic testing consists of the processes and techniques used to determine details about your DNA. Depending on the test, it may reveal changes that affect the health of you and your family. Diagnostic testing is used to confirm or rule out a suspected genetic disorder. The results of a diagnostic test may help you make choices about how to manage your or a family member’s health.

Single gene tests look for changes in one gene and are performed when there is a strong suspicion of a specific disease or condition. For example, single gene tests could be ordered to diagnose Duchene muscular dystrophy or sickle cell disease.

Gene panel tests look for changes in many genes and are usually grouped in categories based on specific types of conditions, such as epilepsy. Gene panel tests can also be grouped into genes that carry higher risks of developing certain cancers.

Whole exome sequencing (WES) involves sequencing all the pieces of an individual’s DNA that provide instructions for making proteins. These pieces of DNA are known as exons and are found within genes. Because changes in the exons are what cause most known diseases, this method can be an efficient way to identify changes that cause disease.

Whole genome sequencing (WGS) is more comprehensive than whole exome sequencing. Research has shown that some genetic disorders are caused by DNA changes that occur outside of the exons. Because of this, whole genome sequencing is useful as this type of testing can identify changes in any part of the genome.

Genomes are large and their bases cannot be ‘read out’ in order (i.e., sequenced) end-to-end in a single step. Rather, to sequence a genome, its DNA must first be broken down into smaller pieces, which can then be read, after which the whole sequence is reassembled. When an entire genome is being sequenced, the process is called “whole-genome sequencing.”

Genomics is a field of biology focused on studying all the DNA of an organism — that is, its genome. Such work includes identifying and characterizing all the genes and functions in an organism’s genome as well as how they interact.

According to the NIH, roughly 80 percent of rare disorders have genetic origins. A large majority of human ailments have some basis in our genes. Until recent decades, doctors were able to take the study of genes, or genetics, into consideration only in cases of birth defects and a limited set of other diseases. Genomic medicine has revolutionized the discovery and development of new treatments and fundamentally transformed clinical practice in many cases.

In some studies, whole genome sequencing has been show to determine the molecular cause of disease—which can include diagnoses—in greater than half of the patients tested. A genetic diagnosis gives clinicians guidance on how to care for children with that rare disease. But there are still benefits even in cases where whole genome sequencing does not yield a diagnosis or yields a diagnosis for a disease that currently lacks an approved therapy. There is clinical value in ruling out diagnoses, and therefore avoiding unnecessary testing and treatments. Additionally, diagnosis of a disease that currently lacks an approved therapy can have significant value to those studying that disease and could catalyze the development of new treatments.

According to the NIH:

“The ability to read the human genome quickly and cheaply has led to substantial advances in discovering the causes of rare disorders. Many families have gone through years of ‘diagnostic odysseys,’ going from one specialist to another trying to find the root cause for their family member’s rare disorder. It is difficult to overstate the relief that genomic testing has brought to many of these patients and families, not just for themselves but eventually for other affected families who are finally able to connect and share their challenges. [That is because] a large number of patient groups have formed after the genomic cause has been identified for a specific rare disorder. These groups allow family members and patients to communicate with each other through social media or conferences.

Perhaps more importantly, many of these patient groups are accelerating research on rare diseases by recruiting patients with the same condition to participate in scientific studies. When families band together, their efforts sometimes shrink the path for establishing the genetic basis for a rare condition from decades (and unfortunately many patient lifetimes) to a year or two.”