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NBME 20 Answers

nbme20/Block 2/Question#6 (reveal difficulty score)
An 18-year-old boy has just been diagnosed ...
50% ๐Ÿ” / ๐Ÿ“บ / ๐ŸŒณ / ๐Ÿ“–
tags: genetics

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 +27  upvote downvote
submitted by โˆ—celeste(96)
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While the lifetime risk in the general population is just below 1%, it is 6.5% in first-degree relatives of patients and it rises to more than 40% in monozygotic twins of affected people. Analyzing classic studies of the genetics of schizophrenia done as early as in 1930s, Fischer concludes that a concordance rate for psychosis of about 50% in monozygotic twins seems to be a realistic estimate, which is significantly higher than that in dizygotic twins of about 10โ€“19% (

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imnotarobotbut  How is one supposed to know this before having read this article? +37
imgdoc  This question falls under the either you know it or you dont category. It isnt in FA or Uworld +2
jaxx  So why would these A-holes put it on there as if prepping for this exam isn't stressful enough :-| +9
doodimoodi  Lol just why seriously +3
champagnesupernova3  This was mentioned in the Kaplan behavioral videos +
usmlecrasher  and there's so much unnecessarily BS instead of real questions +3
j44n  I'm just glad we're seeing this garbage now instead of having an aneurysm in the prometric center +9
feanor  This Question is a perfect example of where you just jump off your seat to demand a refund or you decide to go Antisocial Disorder on your computer screen. +
olddoc  I don't think it has to do with any extra info. The dx is FAP (mutation in APC gene) which is inherited in an AUTOSOMAL DOMINANT fashion ("A" is the mutant allele and "a" is the normal one. The girl in the question stem MUST be heterozygote "Aa", getting the mutant "A" from her sick father and "a" from her healthy mother. Assuming she marries a healthy husband (aa) (this is a normal assumption in genetics questions), their kid will be Aa (the phenotype that will 100% result in CRC) by a probability of 50%. Recall that FAP will 100% progress to CRC is not prophylactically removed. +5
olddoc  FA 2019 Page 381 +
conniea168  It sucks because in psychiatry rotation as MS3 you may come across this fact that rate is ~50% in identical twins, but other than that it's unfair for Step 1 :/ +
epiglotitties  @olddoc wrong q +

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submitted by โˆ—peachespeaches(2)
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Don't need to know this is FAP to get it right.

Father and Grandfather had it, so can assume an AD mutation in this patient. Assuming her partner is homozygous without the mutation, the risk of her AD train going to her child is 50%

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peachespeaches  *AD trait +1
jonobauer  Wrong question +1
jonobauer  Wrong question +1

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