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nbme24/Block 4/Question#47

A 40-year-old man comes to the physician because of ...

HNPCC syndrome

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submitted by neonem(265),

This patient case sounds like he has iron deficiency anemia (anemia, low hematocrit, microcytic) from a GI bleed. To get this question right, you had to remember that the two major inherited GI cancer syndromes are FAP (due to mutation in APC gene, which is a tumor suppressor gene) and Lynch syndrome AKA hereditary non-polyposis colorectal carcinoma (HNPCC), caused by a mutation in a number DNA mismatch repair genes, of with MHS2 is a more common one.

The mechanisms of their carcinoma development are different; in FAP, tumors arise from a normal --> adenoma --> carcinoma sequence while in HNPCC, tumors arise from what's known as a microsatellite instability pathway, leading to spontaneous formation of a carcinoma (not preceded by a benign lesion like an adenoma)... You didn't need to know this to get this question right, but definitely good to know.

medpsychosis  To make it even simpler, if you narrowed it down to FAP vs HNPCC and looked at the image provided in the question, you'd see it's less likely to be FAP due to absence of numerous polyps which would be expected. So HNPCC would be your best choice! +  
yb_26  I always get Li-Fraumeni and Lynch syndromes confused :/ +  

 +1  upvote downvote
submitted by charlie(1),

I think there's a typo on that question. MSH2 gene mutation is the culprit for HNPCC. For MHS2 gene, according to what I just searched, causes Malignant Hyperthermia Susceptibility.

noplanb  Yeah I think it should be MSH +