Clinical characteristics: MUTYH polyposis (also referred to as MUTYH-associated polyposis, or MAP) is characterized by a greatly increased lifetime risk of colorectal cancer (CRC). Although typically associated with ten to a few hundred colonic adenomatous polyps, CRC develops in some individuals in the absence of polyposis. Serrated adenomas, hyperplastic/sessile serrated polyps, and mixed (hyperplastic and adenomatous) polyps can also occur. Duodenal adenomas are common, with an increased risk of duodenal cancer. The risk for malignancies of the ovary and bladder is also increased, and there is some evidence of an increased risk for breast and endometrial cancer. Additional reported features include thyroid nodules, benign adrenal lesions, jawbone cysts, and congenital hypertrophy of the retinal pigment epithelium.
Diagnosis/testing: The diagnosis is established in a proband by identification of biallelic germline pathogenic variants in MUTYH on molecular genetic testing.
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 is appropriate.
Surveillance: Colonoscopy with polypectomy every one to two years beginning at age 25-30 years; upper endoscopy and side viewing duodenoscopy every three months to four years beginning at age 30-35 years with subsequent follow up based on initial findings. Consider annual physical examination, thyroid ultrasound, and skin examination by a dermatologist.
Individuals with a heterozygous germline MUTYH pathogenic variant: offer average moderate-risk colorectal screening based on family history.
Evaluation of relatives at risk: It is appropriate to clarify the genetic status of apparently asymptomatic older and younger sibs of an individual with MAP by molecular genetic testing for the MUTYH pathogenic variants identified in the proband in order to reduce morbidity and mortality in those who would benefit from appropriate surveillance beginning at age 10-15 years and early identification and treatment of polyps.
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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