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wuagbe
To add to this: homozygous HS presents with hemolysis even in absence of stressors. this patient is only presenting with pale skin, and there are no schistocytes on the peripheral smear, so it's a heterozygous ankyrin mutation.
+9
pg32
I wanted to pick hereditary spherocytosis but the mean corpuscular concentration was normal and I thought it was supposed to be elevated? Also, why are there so many RBCs that are way bigger than the spherocytes?
+8
nephroguy
I'm assuming that the MCC is normal because the patient is heterozygous for HS. Not sure if this is correct, but that was my thought process
+1
draykid
Are there any papers that explain the difference in expression of homozygous vs heterozygous HS?
+25
waterloo
I don't know if that matters as much, like the phenotype difference of homozygous or heterozygous for this question. Since you only need one allele to show this, play odds. Is he more likely to have AA or Aa. That was my thought process.
Also if you see spherocytes you'd be going for ankyrin right, not B-globin bc that should be target cells - regardless of MCHC.
+1
alimd
as I remember AD are always heterzygous. Because homozygous are always lethal.
+5
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wuagbe
Several genetics questions on NBME20 appear to be trying to throw us off by changing the descriptions of inheritance, leaving us to assume incomplete penetrance, smh.
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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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poisonivy
The MCV is normal, thalassemias are microcytic anemias, that hint helps to rule out the thalassemias. However, I got it wrong, not sure why it cannot be a homozygous mutation in the ankyrin gene
+2
adong
@poisonivy, other commenter pointed out it's autosomal dominant so best answer would be heterozygous
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victor_abdullatif
edit #1: made a typo. meant to say "the patient's symptoms are NOT severe"
sorry about that!
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l0ud_minority
Yes I don't understand why the MCHC is normal that is still not what is expected. I wish NBME provided answer keys and cited their sources for their rationale.
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ibestalkinyo
This is what threw me off; I figured with 2 unaffected parents, it's more likely he had an autosomal recessive mutation.
+1
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xxabi
How do you know is autosomal dominant?
+3
scpomp
Hereditary spherocytosis
+1
fshowon
Isnt the mean corpuscular hemoglobin concentration increased in spherocytosis? Thats what through me off.
+5
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
+4
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 โnala_ula(127)
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).