What is cascade testing, why is my doctor asking me to share my genetic result?

[Anonymous]

What is cascade testing, and why is my doctor asking me to share my genetic result with my family?

[Genetic Counselor]

Cascade testing is the process of offering genetic counseling and testing to the blood relatives of a person who has been found to carry a disease-causing genetic change. The first person in the family to be diagnosed is called the index patient. Once the exact genetic change in the index patient is known, relatives can be checked for that one specific change. The testing then “cascades” outward through the family: first to the closest relatives, and then, for anyone who also tests positive, on to their own close relatives.

The reason this matters is simple. You share part of your DNA with your parents, brothers and sisters, and children. If you carry a genetic change that raises the risk of a serious condition, some of them may carry it too, often without knowing. For many conditions, knowing early changes what happens next. A relative who carries a hereditary cancer gene change can begin earlier or more frequent screening. A relative with familial hypercholesterolemia, an inherited cause of very high cholesterol, can start treatment years before a heart attack. A couple who both carry beta-thalassemia can plan a pregnancy with full information.

The Centers for Disease Control and Prevention in the United States lists three groups of conditions where cascade testing has the strongest evidence of saving lives: hereditary breast and ovarian cancer (BRCA1 and BRCA2), Lynch syndrome (a hereditary colon and womb cancer condition), and familial hypercholesterolemia. But the same approach applies to many other conditions, including thalassemia, Duchenne muscular dystrophy, inherited heart rhythm and heart muscle conditions, and Fragile X syndrome.

Cascade testing is also efficient. An Indian study of beta-thalassemia families found that testing the relatives of affected children identified carriers at 5 to 6 times the rate of general population screening. Relatives of a known patient are simply much more likely to carry the same change than a random person.

Your doctor is not asking you to test your family. They are asking you to let your family know that an option exists, so each relative can decide for themselves.

[Author]

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