Last Modified: May 14, 2009
Dear OncoLink "Ask The Experts,"
FAP (familial adenomatous polyposis) is very prevalent in our family. I lost my husband at 33 y.o. and his brother at 38 y.o. to colon cancer, at which time it was discovered that FAP was the culprit. Two of my sons were diagnosed, one died of the disease, and one is alive and well today. I also lost one grandson at the age of 18 to the disease. I have a 37-year-old daughter who has not presented with any polyps or other symptoms of FAP. Do you feel [that] it is safe to say that she does not have the mutation? My son has had 3 genetic tests done in an effort to locate his mutation so that my daughter and her 2-year-old son could get blood tests to see if they have it, but they have not been able to locate the mutation in any of the affected family members.
Jill Stopfer, MS, CGC, Certified Genetic Counselor, responds:
Your daughter is at a 50% risk of having the gene that leads to FAP, since one parent had the gene and one does not. A woman who is at 50% risk for FAP, but who has had consistently clean colonoscopies with no polyps and who is already 37 years old,is most likely not carrying the FAP gene. There is only a very small chance that she will start to develop polyps at this point, but since there is still a small chance, she should continue to have periodic colonoscopies. If she is basing her conclusion on the lack of symptoms only, and has not had colonoscopy screening, then we cannot make any judgments at this point.
Genetic testing for mutations in the APC gene that leads to FAP has improved over the last several years, and is a little more sensitive and able to find mutations now than in the past. A genetic counselor can look at the genetic testing report and determine if testing was done by sequencing, including testing for large deletions and rearrangements. If this type of sequencing testing was done, and no mutation was detected, then there is nothing else to do at this point testing-wise. The story of your family clearly represents FAP, and hopefully there will be technological enhancements in the future that allow for more informative testing in more families. If a family member with FAP has not yet had the testing mentioned above, it would be a good idea to have the testing done. Until then, everyone at 50% risk for FAP needs to start colonoscopy screening between 10 and 12 years.