What Can 23andMe Results Tell You About Your Colorectal Cancer Risk?

By Eleanor Griffith, MS, CGC · Jan 2019

23andMe announced FDA approval to report on the two most common variants in the MUTYH gene. For most people — the answer, once again, is not too much.

What Is MAP and Who Has It?

Carrying mutations in both copies of the MUTYH gene confers significantly increased colorectal cancer risk — this autosomal recessive condition is called MAP (MUTYH-Associated Polyposis). Since MAP is recessive, individuals with MAP typically don't have a strong family history of colorectal cancer. Learning you have MAP could be life-saving: with colorectal cancer, removing polyps can actually prevent cancer from developing, unlike breast cancer where the goal is early detection and treatment.

The Math

About 1-2% of individuals of European ancestry are estimated to carry one MUTYH mutation. To have MAP, you need mutations in both copies. Assuming a 2% carrier rate: 1/50 × 1/2 × 1/50 × 1/2 = 1/10,000. The odds of having MAP are very low in the absence of family history. If you have a family history of colorectal cancer, this test probably isn't what you need — most familial colorectal cancer is not due to MUTYH. Lynch syndrome is a far more common culprit, and comprehensive clinical testing would be a more appropriate starting point.