MUTYH-Associated Adenomatous Polyposis Factsheet

MUTYH-associated adenomatous polyposis (MAP) is a cancer predisposition syndrome caused by having two MUTYH gene mutations. Carriers of one MUTYH gene mutation have a milder clinical presentation.

Clinical Features

Individuals with MAP typically develop dozens (sometimes hundreds) of adenomatous colon polyps, although the presentation can vary from an absence of polyps to over a thousand polyps. Without surveillance, patients with MAP have a nearly 100 percent risk of developing colon cancer. In addition to colon polyps, individuals with MAP may also develop gastric and duodenal adenomas and nonadenomatous polyps, such as serrated and hyperplastic polyps. MAP is not associated with any unique physician exam findings.

Cancer Risks Associated with MAP

Individuals with MAP have nearly 100 percent risk of developing colorectal cancer by the age of 65 and a 5% risk of developing duodenal cancer. Research is ongoing to determine what other cancers may be linked to MUTYH gene mutations.

Tumor Characteristics

A molecular hallmark of cancers caused by MAP is the presence of a specific somatic KRAS variant (c.34G>T in codon 12) which is found in 64% of MAP colorectal cancers.

Prevalence of MAP

About 0.7% of all colorectal cancer is due to MAP. An estimated 1 in 20,000-40,000 individuals of northern European ancestry have MAP (carry two MUTYH gene mutations). It is estimated that 1%-2% of this population carries one MUTYH mutation. MAP may be less frequent in other specific ethnic populations.

Diagnosis

A diagnosis is established in individuals with clinical characteristics who have two mutations identified in the MUTYH gene.

Genetic testing is recommended for individuals with ≥ 20 polyps, and may be considered in individuals with 10-20 polyps with other personal and/or family features.

Genetics & Inheritance

MAP is an autosomal recessive condition caused by mutations in both copies of an individual’s MUTYH genes. Siblings of an individual with MAP have a 25% chance of also having MAP (inherit two mutations) and a 50% chance to be a carrier (inherit one mutation). Other first-degree relatives (parents, children) have a 50% chance to be a carrier. Men and women are equally likely to inherit, and pass on, a mutation.

Clinical Testing

Clinical testing includes gene sequencing and deletion/duplication analysis. Sequencing detects 99% of individuals with MAP.

Testing may be for MUTYH gene mutations alone or as part of a multi-gene panel that includes genes predisposing for other polyposis syndromes. Because MAP is autosomal recessive, MUTYH gene testing may be performed prior to APC gene or multi-gene testing if a recessive pattern is apparent, such as only siblings affected.

Management

Screening recommendations vary depending on whether an individual is affected or unaffected with cancer, has two mutations (MAP) or one mutation (carrier), has a family history of colorectal cancer, and polyp burden. Refer to NCCN guidelines for specific recommendations.

For individuals with MAP, increased colorectal and gastrointestinal surveillance (colonoscopy and esophagogastroduodenoscopy) are recommended. Subtotal colectomy or proctocolectomy may be considered depending on polyp burden.

Management of MUTYH Gene Carriers

Current guidelines recommend increased colonoscopy screening for MUTYH carriers. In a large population-based study, carriers had a moderately increased risk of colorectal cancer compared to the general population (2.5 times greater). Other studies have not shown this increased risk consistently; therefore, more research is needed to inform clinical management. 

Other Genes that Contribute to Polyposis

There are other hereditary cancer syndromes that increase the risk for polyps and colorectal cancer, including familial adenomatous polyposis (FAP), attenuated familial adenomatous polyposis (AFAP), Juvenile Polyposis syndrome, Peutz-Jeghers syndrome, and Cowden syndrome. The presentation of these syndromes in a family may overlap with that of MAP, but can sometimes be distinguished based on characteristic features, such as physical exam findings and polyp pathology. In addition, a number of common genetic susceptibility variants are thought to increase polyp and colorectal cancer risk, indicating there are likely other genes that contribute to polyp development which have not yet been identified. See GeneReviews for more information about the genetic differential diagnosis for MAP.

Select Guidelines & Resources

Resources

GeneReviews (2015): MUTYH-associated polyposis.

American Society of Clinical Oncology (2017): MYH associated polyposis.

National Cancer Institute (2015): Genetics of Colorectal Cancer PDQ – Major Genetic Syndromes.

Guidelines

National Comprehensive Cancer Network (2016): Genetic/Familial High Risk Assessment: Colorectal (Free registration required for access).

American College of Gastroenterology (2015): Clinical Guideline on Genetic Testing and Management of Hereditary Gastrointestinal Cancer Syndromes.

American College of Medical Genetics & National Society of Genetic Counselors (2014): Referral indications for cancer predisposition assessment.