Someone in My Family Has FAP; Should I Also Be Tested?

Emily Malcolm, PhD avatar

by Emily Malcolm, PhD |

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You may have a family history of familial amyloid polyneuropathy (FAP) and be wondering if you might also have the disease. To make an informed choice about getting tested, it is important to understand what causes FAP, how the disease is inherited, and what a genetic test entails.

What causes FAP?

FAP is caused by mutations in a gene called TTR. Mutations in this gene cause the TTR protein to misfold. The misfolded proteins aggregate into clumps (also called amyloids), which interfere with cell functions.

How is FAP inherited?

FAP is inherited in a dominant pattern, meaning you may develop the disease if you inherit a single copy of a disease-causing mutation from one of your parents.

If a person with FAP has a child with someone who does not have the disease, their children will have a 1 in 2 chance of inheriting the disease-causing mutation and may develop the disease. If two people with FAP have children together, their children will have a 3 in 4 chance of inheriting one or more copies of a disease-causing mutation and may develop FAP. They will have a 1 in 4 chance of inheriting two healthy copies of the gene and not having FAP.

What is genetic testing?

To carry out a genetic test, your healthcare provider will collect a small amount of blood. They will send this blood sample to an independent laboratory to determine if you have disease-causing mutations in your TTR gene. It is important to note that having a disease-causing mutation does not mean you will definitely develop symptoms of FAP because of a genetic phenomenon called penetrance.

You should discuss your family history of the disease with your primary care physician to determine whether testing is necessary. Based on the results of the test, your doctor may recommend you see a genetic counselor.

When to get tested?

In cases where one of your immediate family members (parents or siblings) has FAP, it is a good idea to undergo genetic testing to determine if you might also have the disease-causing mutation.

If the family member who has the disease is a cousin, it is unlikely you will have inherited the disease-causing mutation. If the relative is an aunt or uncle, your parents may need to be tested, and if their tests are positive for mutations, you also should get tested.

 

Last updated: April 9, 2020

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