Genome Sequencing

All of our DNA together is called the genome. This includes our genes as well as the genetic material between our genes. Genome sequencing is a type of genetic test that sequences every letter of your DNA. In this section, we explain genome sequencing and the different types of results.


All of our DNA together is called the genome. About 1 % of the genome is called the exome; which includes over 20,000 genes.

There is also a lot of genetic material between these genes, but that is still part of the DNA sequence. The parts between the genes are also important for the body to function and they make up the remainder of the genome.

Sequencing every letter of your DNA is called “genome sequencing.” Genome sequencing can have different types of results.

A positive result means that a genetic test identified a change in a gene that we are confident causes the features in you or your child. Another word that you may see on a report to describe a positive result is “pathogenic”.

A likely positive result means that a genetic test identified a change in a gene that is suspected to cause the clinical findings in you or your child, but there may not be enough scientific information known at this time to say it is definitively positive.

A negative result means that there were no gene changes identified by the testing method that could explain your or your child’s clinical findings.

A variant of unknown clinical significance is a genetic change that, based on the currently available scientific knowledge, cannot be interpreted as pathogenic or negative.

In the future, scientists are likely to discover what these variants of unknown clinical significance mean. Until then, receiving results with a variant of unknown clinical significance can be understandably frustrating as we can’t interpret what the DNA change means for your child or family.

A candidate gene change means that there is a change in a gene that is likely to affect the function of the protein encoded by this gene, but changes in the specific gene have not been linked to any human disease to date. These gene changes are like variants of unknown clinical significance in that we cannot usually act on these changes. As scientists learn more about a candidate gene, this result may be better understood. As other individuals are identified with mutations in the same “novel” genes, a candidate gene may, in time, become a known disease-causing gene.

Keep in mind, genetic testing does not always find an explanation for medical symptoms.

The absence of a positive genetic testing result does not take away an individual’s clinical diagnosis.

Also, a non-diagnostic genetic testing result does not mean that the condition is not genetic. Instead it may mean that the testing completed was not able to identify a genetic cause at this time.*

Since genome sequencing looks at all of our genes, we may also find variants in genes that are unrelated to the reason for doing this test. These are called “secondary findings.”

The laboratory will only report secondary findings that are medically actionable if they are identified in the primary patient. Medically actionable means that a mutation in a specific gene can lead to a medical condition for which there are well-defined medical management guidelines with a potential to improve the outcome. Changes in medical management range from starting a new medication, to undergoing screening tests to detect a specific condition at its earliest presentation when treatments can be most effective.

It is your choice whether or not you and your family want to learn about secondary findings. You can either opt in to get results, or opt out if you’d rather not receive these secondary findings. Unexpected secondary findings are identified in approximately 4-5 percent of families undergoing a genome sequencing test. Please remember, that there is no right or wrong choice about secondary findings. Each family makes their own choice that is right for them. Your genetic healthcare provider will help you through this decision-making process.