Pt with h/o prolonged bleeding after tooth extraction - USMLE Forums
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  #1  
Old 07-19-2010
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Genetics Pt with h/o prolonged bleeding after tooth extraction

A 14-yr-old male had severe prolonged bleeding after having a tooth extracted. He also has a h/o multiple episodes of painful joint swellings following minor trauma; evaluation revealed he had inherited disorder, now his older sister, who
doesn't have this condition, asks about the risk that her own children will be affected. The best probabble estimate:

A) near zero
B) 1/2
C) 1/4
D) 1/8
E) 1/16
F) 1/32
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  #2  
Old 07-19-2010
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does the pt have von willibrand type 1 disease ???

am i correct ???
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Old 07-19-2010
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Search genetics q

is the answer 1/2??
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Old 07-19-2010
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how do u know if its vWB? it could be hemophilia?

if it's hemophilia i think the answer should be near zero because its x-linked.
what do u guys think?
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Old 07-19-2010
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It really could be either, but the qbanks usually give you more in the vignette so you can distinguish one bleeding problem from another. Near zero sounds good if I had to guess.

Can someone show me what I'm missing?
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Old 07-19-2010
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Post pt wit h/o prolonged bleeding

if this is the only info given in the questn we can safely assume that they are talking abt vw disease and not haemophilia because prevalence of vw is 1/100 in US population,while for hamophilia which is much rarer its 1/10,000....

and VW-A being more common,it is inherited in autosomal domnant fashion... so ans may be 1/2....pls correct me if am wrong..
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Old 07-19-2010
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I'm gonna go with D... Here is my reasoning:

I am assuming its hemophillia A because:
sister is not affected (more likely X-linked)
hemoarthorsis is present

If that is the case... the patient's mother must be a carrier (father cannot pass down to affected son)
The patient's mother has a 50% chance of passing the mutated X chromsome to the patient's sister
Now if the sister has a daugther... there is 50% chance that she will give her defected gene but this will be masked (unless unfavourable lyonisation occurs). If the sister has a son...ther is a 50% chance that she will giver defected X chrmosome and since the father gives a Y... the son will have hemophillia.
So we are dealing with two dependent events: the likely hood of having an affected child (1/4) if she is a carrier (1/2) = 1/8
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Old 07-20-2010
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inder is ryt!!!


it is hemophilia and as u know it is x linked disease ..so if brother is having disease and she doesnt that means most likely her mother is carier and father normal.. so she has 1/2 chance of being a carrier as when u cross carier mother of this girl with normal father one girl is normal and other is carrier so =1/2
now if she mates with normal male as she should coz its not mention of her husband so out of 2 gals and 2 boys only one boy will be diseased ..so = 1/4!
so probability of her children will be 1/2 * 1/4 =1/8
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Old 07-20-2010
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Help query

i get Inder's reasoning but why haemophilia in first place???why not Vw disease??
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yup i have the same question why not vW disease ??/
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  #11  
Old 07-21-2010
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Default It is hemophila

Platelet abnormality -petichae--VW disease
Coagulation abnormality-joint bleeding---hemophilia
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