A 30-year-old man is found to have 25 colorectal adenomas. His brother had similar polyp burden, but both parents, examined by colonoscopy, are normal. Genetic analysis of APC is negative. Which genetic diagnosis best fits this pedigree?
- A Classic familial adenomatous polyposis with a de novo APC mutation
- B Lynch syndrome due to MLH1 mutation
- C MUTYH-associated polyposis inherited in an autosomal recessive pattern ✓
- D Attenuated FAP with incomplete penetrance of an APC mutation
Correct answer: C. MUTYH-associated polyposis inherited in an autosomal recessive pattern
Explanation
Biallelic MUTYH mutations cause an autosomal recessive polyposis syndrome with typically 10 to a few hundred adenomas appearing at a younger age than sporadic disease. Unaffected carrier parents with affected offspring, horizontal spread to siblings, and a normal APC gene are hallmarks of recessive inheritance. Attenuated FAP is autosomal dominant and would show vertical transmission through an affected parent.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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