For children dealing with rare childhood conditions and their families, whole-genome sequencing (WGS) can be a game-changer. The innovative genomic technique allows scientists and doctors to examine the genes to search for possible genetic causes for your child’s condition.
The doctors and scientists at TGen’s Center for Rare Childhood Disorders (the Center) perform exome sequencing to identify rare childhood disorders that standard tests cannot detect.
- What is the exome?
The human genome, or a person’s complete set of DNA, consists of three billion “letters” (called base pairs). The base pairs are all crammed into 23 pairs of thread-like structures called chromosomes and can be found in every cell of the body. A particular sequence of the DNA forms a gene. Genes are written in code that spell out the instructions to make a protein. People generally have two copies of most genes, one copy from each parent.
Only about one to two percent of genes provide instructions or codes for proteins, the building blocks of cells. The coding portion of the genome is called the exome.
- What is genome sequencing?
Genome sequencing is a single test used to pinpoint many genetic disorders. Scientists use high-tech machines to analyze blood (or tissue samples) from you or your child to read the genetic code of about 20,000 genes. They are searching for any changes that could lead to differences in how the body grows and develops.
Unlike some types of genetic testing, which analyzes single genes one by one, genome sequencing technology can analyze many genes all at once.
- How is genome sequencing done?
A blood sample from your child is required to perform genome sequencing. Oftentimes blood samples from parents or other family members are also tested. Occasionally, other tissue types (for example, skin cells or cheek swabs) are used.
DNA is extracted from these blood or tissue samples and then analyzed. The laboratory isolates DNA from the blood sample. The exomes (coding parts) and introns (non-coding parts) of most genes will be examined for both the person having sequencing and any family members who give DNA for comparison.
- Why perform genome sequencing?
Whole genome sequencing (WGS) is done to find a genetic cause of your child’s signs and symptoms. It’s one of the most extensive genetic tests available. Because WGS looks at more genes than most genetic tests, it may find a genetic cause for your child’s disorder even if previous genetic testing did not.
- What are the benefits of WGS?
Ideally, WGS may discover a genetic cause for your child’s condition, which can help guide medical care. It can help individuals participate in additional research focused on their specific disorder and connect with other individuals who also have the same symptoms. A genetic diagnosis may also give your family information about the chance that you could have other children affected with the same condition. This information may also be helpful for other family members.
- Are there limitations to WGS?
Although WGS is a powerful, breakthrough diagnostic tool, it’s not a perfect test, and it may not uncover the reason for your child’s disorder. In addition, WGS does not detect certain types of mutations, so WGS may not find some mutations present in the DNA. WGS also costs more than whole exome sequencing (WES) which looks specifically at the coding region of the DNA. While whole genome sequencing is not covered by insurance companies at this time and is mostly used in research settings, many insurance companies do cover the cost of WES as a clinical test.
- How accurate is WGS?
The technology is still relatively new, and it is not yet possible to capture and sequence 100 percent of the exome at high quality. However, experts estimate that it’s possible to capture approximately 99.4 percent of the exome.
- How much does WES and WGS cost?
In 2015, the cost to generate a whole-exome sequence was reported to be generally below $1,000, although that can vary. Through the generosity of donors, the Center provides genomic testing for families at no charge and continues its work to provide solutions and cures to families and their children.
Genome sequencing is an exciting solution that uncovers the complex and unsolved childhood conditions and provides hope for treatments.
