As a genetic counselor, you are asked to assess the risk for a couple with a family history of familial adenomatous polyposis (FAP) who are thinking about having children. Neither the husband nor the wife has colorectal cancer, but the husband has a sister with FAP. What is the probability that this couple will have a child with FAP? Are there any tests that you could recommend to help in this assessment?

Key Concepts

Familial Adenomatous Polyposis (FAP)

Familial Adenomatous Polyposis (FAP) is a hereditary condition characterized by the development of numerous polyps in the colon and rectum, which significantly increases the risk of colorectal cancer. It is caused by mutations in the APC gene, and individuals with FAP typically have a 100% risk of developing colorectal cancer if untreated. Understanding FAP is crucial for assessing genetic risks in families with a history of the condition.

Autosomal Dominant Inheritance

FAP follows an autosomal dominant inheritance pattern, meaning that only one copy of the mutated gene from an affected parent can lead to the condition in offspring. In this case, the husband’s sister has FAP, indicating that the husband may carry the mutation. This concept is essential for calculating the probability of the couple's children inheriting the condition, as each child has a 50% chance of inheriting the mutated gene if the father is a carrier.

Genetic Testing and Counseling

Genetic testing can identify mutations in the APC gene, providing critical information for assessing the risk of FAP in the couple's children. Genetic counseling can help the couple understand their options, including testing for the husband to determine if he carries the mutation. This process aids in informed decision-making regarding family planning and potential surveillance strategies for early detection of colorectal cancer.