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NBME 20 Answers

nbme20/Block 3/Question#11

A 3-year-old boy is brought to the physician ...

Heterozygous mutation in the ankyrin gene

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submitted by nala_ula(35),

The histology is of spherocytes (small spherical cells w/o central pallor). Hereditary spherocytosis is due to defect in proteins interacting with RBC membrane skeleton and plasma membrane (ankyrin, band 3, protein 4.2, spectrin). Mostly autosomal dominant inheritance (so heterozygous mutation since you only need one mutant allele to get the disease).





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submitted by dr_jan_itor(10),

Can anyone answer why this one can't be F. Beta thalasemia major? I was thinking becaues of his anemia and the "european descent" which includes the mediteranian europeans. Unless NMBE writers think that european only means the ones with extra white people lol

dickass  European implies northern european (they even specified the patient was a person of pallor), mediterranean descent is usually implied by country of origin or by straight-out writing 'mediterranean'. +  




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submitted by strugglebus(68),

Auto dom disease are usually heterozygous (or so they want us to assume)

xxabi  How do you know is autosomal dominant? +1  
scpomp  Hereditary spherocytosis +  
fshowon  Isnt the mean corpuscular hemoglobin concentration increased in spherocytosis? Thats what through me off. +  
charcot_bouchard  yes, would be inc in prev NBME. But this is batshit nbme 20. U have to identify spherocytes without central pallor in PBF +1  
charcot_bouchard  yes, would be inc in prev NBME. But this is batshit nbme 20. U have to identify spherocytes without central pallor in PBF +  




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submitted by xw1984(0),

I got this Q wrong. I was wondering why this patient “has no personal or family history”. Hereditary spherocytosis should be a AD disease, so, generally speaking, this diz should be seen in each generation, right?

step1soon  I was thinking the same! +