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MUTYH-Associated Polyposis.

Source

GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2018.
2012 Oct 4 [updated 2015 Sep 24].

Author information

1
Department of Clinical Genetics, Leiden University Medical Center, Leiden, Netherlands
2
Chairman, Preventive Medicine and Public Health, Professor of Medicine, Director, Hereditary Cancer Center, Creighton University, Omaha, Nebraska
3
Department of Medicine, Division of Gastroenterology, Hepatology, and Nutrition, University of Pittsburgh, Pittsburgh, Pennsylvania

Excerpt

CLINICAL CHARACTERISTICS:

MUTYH-associated polyposis (MAP), caused by biallelic pathogenic variants in MUTYH, is characterized by a greatly increased lifetime risk of colorectal cancer (CRC) (43% to almost 100% in the absence of timely surveillance). Although typically associated with ten to a few hundred colonic adenomatous polyps that are evident at a mean age of about 50 years, colonic cancer develops in some individuals with biallelic MUTYH pathogenic variants in the absence of polyposis. Duodenal adenomas are found in 17%-25% of individuals with MAP. Serrated adenomas, hyperplastic/sessile serrated polyps, and mixed (hyperplastic and adenomatous) polyps can also occur. The lifetime risk of duodenal cancer is about 4%. Also noted are a modestly increased risk for rather late-onset malignancies of the ovary, bladder, and skin, and some evidence for an increased risk for breast and endometrial cancer. Some affected individuals develop sebaceous gland tumors and more recently, thyroid abnormalities (multinodular goiter, single nodules, and papillary thyroid cancer) have been reported.

DIAGNOSIS/TESTING:

The diagnosis is established in individuals with characteristic clinical findings and biallelic germline MUTYH pathogenic variants.

MANAGEMENT:

Treatment of manifestations: Suspicious polyps identified on colonoscopy should be removed until polypectomy alone cannot manage the large size and density of the polyps, at which point either subtotal colectomy or proctocolectomy is performed. Duodenal polyps showing dysplasia or villous changes should be excised during endoscopy. Abnormal findings on thyroid ultrasound examination should be evaluated by a thyroid specialist to determine what combination of monitoring, surgery, and/or fine needle aspiration (FNA) is appropriate. Surveillance: Individuals with biallelic germline MUTYH pathogenic variants: In the US: pan colonoscopy every one to two years beginning at age 25-30 years; following colectomy, endoscopy of any remaining colon or rectum every one to two years. Upper endoscopy and side viewing duodenoscopy beginning at age 30-35 years with subsequent follow up based on initial findings, analogous to FAP using the Spigelman criteria. No consensus exists for screening for thyroid abnormalities. For extraintestinal malignancies surveillance is as for existing protocols offered to the general population. In Europe: pan colonoscopy beginning at age 18-20 years; upper endoscopy with side viewing duodenoscopy beginning at age 25-30 years; follow up depending on disease severity using the Spigelman criteria. Individuals with a heterozygous germline MUTYH pathogenic variant: offer average moderate-risk colorectal screening based on family history. Evaluation of relatives at risk: Offer molecular genetic testing for the familial pathogenic variants to all sibs of an individual with genetically confirmed MAP in order to reduce morbidity and mortality through early diagnosis and treatment.

GENETIC COUNSELING:

MAP is inherited in an autosomal recessive manner. At conception, each sib of an affected individual has a 25% chance of being affected, a 50% chance of being a carrier with a small increased risk for CRC, and a 25% chance of being unaffected and not a carrier. Carrier testing for at-risk family members and prenatal diagnosis for pregnancies at increased risk are possible if the pathogenic variants in the family have been identified.

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