What is familial cascade genetic testing, and why is it important?
09.JAN.2024
Written by Anna Sanniti
Reviewed by Wendi Gill, CGC
Cascade testing is the process of telling family members about a genetic condition that has been discovered through genetic testing. This is followed by family members getting tested for the condition. This is done because inherited conditions are passed down in families. If one family member has an inherited condition, there is a chance that family members may have the same genetic condition.
Many people do not know they have a genetic condition until symptoms begin to appear. Cascade testing is important as it allows finding people with genetic conditions before they develop symptoms. This allows them to take steps to prevent disease or treat it early. [1]
In this article, we will discuss:
How cascade testing works
How to share your genetic testing results or a diagnosis with your family members
Cascade testing for Hereditary Breast and Ovarian Cancer syndrome, Lynch syndrome, and Familial Hypercholesterolemia
How does cascade testing work?
First-degree relatives (children, parents, and siblings) should be tested first. They are the most likely to have the same genetic variant identified in you. Testing then “cascades” through the family depending on the results. For example, if testing shows that your mother has the same genetic variant as you, testing would be recommended for your maternal family members. Paternal family members would likely not need to be tested. [1]
Cascade testing for Hereditary Breast and Ovarian Cancer, Lynch Syndrome, and Familial Hypercholesterolemia
Cascade testing for Hereditary Breast and Ovarian Cancer syndrome, Lynch syndrome, and Familial Hypercholesterolemia is very important, as these are inherited conditions. [2-4]
If you have a BRCA1, BRCA2, Lynch syndrome, or Familial Hypercholesterolemia genetic variant:
Your mother, father, children, and siblings have a 1 in 2 (50%) chance of having the same genetic variant. [2-4]
Your half-siblings, aunts, uncles, grandmothers, and grandfathers have a 1 in 4 (25%) chance of having the same genetic variant. [2-4]
Your cousins and more distantly related family members have as much as a 1 in 8 (12.5%) chance of having the same genetic variant. [2-4]
If you have the rare form of Familial Hypercholesterolemia (FH) called homozygous FH, your family members will have even higher chances of FH or homozygous FH. This is because you have a genetic variant in both copies of the gene, instead of just one. [4]
Let’s recap
Cascade testing is the process of letting other family members know of a genetic condition discovered through genetic testing. This is followed by family members getting tested for the condition.
Cascade testing is important as it allows finding people with genetic conditions before they develop symptoms. This allows them to take steps to prevent disease or treat it early.
Family members most likely to share your condition, such as your children, parents, and siblings should be tested first.
From there, testing “cascades” through the family depending on who has a positive test result and who does not.
A genetic counselor or healthcare provider can help with this process
You should encourage your family members to tell their provider as soon as possible. This means they can be referred to a genetic counselor and be tested.