Genetic testing for adenomatous polyposis syndromes may have significant meaning not only for the individual initially tested, but also for his/her family members.

Gene mutations in the APC gene (leading to FAP or AFAP) are passed on in families in an autosomal dominant pattern. This means that an individual with an APC mutation has a 50% (or 1 in 2) chance of passing that mutation on to each of his or her offspring. Often, an individual inherited their mutation from a parent. Knowing if the mutation came from the mother or father is helpful, because other, more distant family members on that side of the family (aunts, uncles, cousins, etc.) may also carry the same mutation. However, 20-30% of the time, an APC mutation will be a new mutation and there will be no family history of colorectal polyps or cancer.

Gene mutations in the MYH genes (leading to MAP) are passed on in families in an autosomal recessive pattern. This means that, in order for an individual to be affected with MAP, he or she would have inherited mutations in both copies of the MYH genes, one from each parent. Parents of this individual are considered "carriers" of a single MYH gene mutation but are usually not affected with colorectal polyps or cancer. In most cases, children of affected individuals will be "carriers" of a single MYH gene mutation as well. Siblings of the patient are at 25% risk to carry the same two mutations in their MYH genes. Due to the autosomal recessive pattern of inheritance, individuals affected with MAP will often have no family history of colorectal polyps or cancer.

» Adenomatous Polyposis Syndromes: Frequently Asked Questions

A genetic test for adenomatous polyposis syndromes