Genetic testing for adenomatous polyposis syndromes is not only significant for the person tested, but for the person’s family as well.
Gene mutations in theAPC gene (leading to FAP or AFAP) are passed on to families in an autosomal dominant pattern — meaning that someone with this mutation has a 50% chance of passing it on to each of his or her children
Often an individual inherited their mutation from a parent; however, 20% to 30% of the time, an APC mutation will be new and there will be no family history of colorectal polyps or cancer
Knowing the mutation came from the mother or father is helpful, because other family members on that side of the family (aunts, uncles, cousins, etc.) may also carry the mutation
MYH mutations (leading to MAP) are passed on in an autosomal recessive pattern — meaning that a MAP-affected individual inherited mutations in both copies of the MYH genes (one from each parent)
Parents of this individual are considered “carriers” of a single MYH mutation, but are usually not affected with colorectal polyps or cancer
Children of affected individuals will usually be carriers of a single MYH mutation
Siblings of the patient are at a 25% risk of carrying the same 2 mutations in their MYH genes
The autosomal recessive pattern of inheritance means that those affected with MAP often have no family history of colorectal polyps or cancer
