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MYH-associated polyposis (MAP) is an autosomal recessive condition that results in an excessive number of polyps in the colon (polyposis), with an increased lifetime risk of colorectal cancer
Inheritance: Autosomal recessive
→ Affected individuals have two mutated MUTYH copies.
→ Carriers (one mutation) usually have a slightly increased colorectal cancer (CRC) risk.
Typical presentation:
Dozens to hundreds of adenomatous colon polyps (often fewer than classic FAP)
bowel cancer often develops in adulthood (commonly 40s–60s)
Cancer risks:
Colorectal cancer: high lifetime risk
Increased risk (to varying degrees) of duodenal, gastric, ovarian, bladder, skin, and possibly breast cancers
Colonoscopy:
Start ~age 25–30, every 1–2 years
Upper GI endoscopy:
Start ~age 30–35, interval based on findings
Surgery:
Consider colectomy if polyp burden can’t be controlled endoscopically
Family testing:
Test siblings (25% risk if both parents are carriers)
Partners may be offered carrier testing for reproductive planning
Genetics note
MUTYH is involved in base excision repair of oxidative DNA damage. Loss of function leads to accumulation of mutations, especially G:C → T:A transversions.