NBME 18 2 of 3 (NBME Answers)

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Retired NBME 18 Answers

nbme18/Block 4/Question#10 (reveal difficulty score)
5 to girl is brough to physician because of ...
2 of 3 🔍 / 📺 / 🌳 / 📖
tags: genetics

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submitted by ∗motherhen(69)

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Kartagener syndrome, an autosomal recessive ciliary disorder. Presents with triad of chronic sinusitis, bronchiectasis and situs inversus.

Since the brother is known to be phenotypically normal, he can either be AA, Aa or Aa. Thus, there is a 2/3 chance is a carrier.

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stefanmil Can you explain how is this Kartagener? It didn't come to my mind at all :/ thanks +

kcd0321 I thought it was Cystic fibrosis: chronic cough with "thick" green sputum, cramps in the abdomen (malabsorption issues because of pancreatic insufficiency maybe), and then the frequent respiratory infections. Its also AR so the same principle of AA, Aa, or Aa, so he has a 2/3 chance of being a carrier. +8

srmtn isn't Aa or aA the same in terms of heterozygosity? I thought about that and put 1/2 :/ +

chj7 @srmtn They represent two different events: getting the "bad" allele from the mom OR the dad. Thus, they individually contribute to the risk of being a carrier. +

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submitted by geekymle(11)

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what i dont understand of this question is that why is cystic fibrosis causing hyperinflated lungs?

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spartanmd I believe the decreased clearance of respiratory secretion causing difficulty to exhale and air trapping. Chronic air trapping causes hyperinflation of the lungs and clubbing of the hands. +

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submitted by ∗beltorres23(10)

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Sister has Cystic Fibrosis (AR), brother is "healthy" does not have Cystic fibrosis, but has asthma. Because he is "healthy" he does not have cystic fibrosis -> so he is either a carrier (2/3) or a non carrier (1/3).

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