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#1
05-27-2011
 USMLE Forums Addict Steps History: 1+CK+CS Posts: 160 Threads: 15 Thanked 77 Times in 57 Posts Reputation: 88
Calculating the risk of cleft palate for these parents

A male new born at 39 wks gestation has a unilateral cleft lip and palate. studies shown that concordance for this trait in MZ twins 0.40 and DZ twins 0.04. the incidence of cleft lip and palate in general population is 0.001 if the parents of this newborn have a second child the risk for unilateral cleft lip and palate in this child is approximately which?

A) 75%
B) 50%
C) 25%
D) 4%
E) 0%

hi guys iv got this Q and i need ur help in approaching the correct answer
 The above post was thanked by: bebix (05-28-2011), Claus_CU (05-28-2011), Hamada (09-30-2014)

#2
05-27-2011
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,175 Threads: 38 Thanked 854 Times in 478 Posts Reputation: 864

Assuming the parents dont have twins (can't really calculate I think), it would be comparing to the General Population where incidence is 1/1000.

I would go with D) 4%

I have no idea!
#3
05-28-2011
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,357 Threads: 194 Thanked 3,268 Times in 881 Posts Reputation: 3278

Quote:
 Originally Posted by patelMD Assuming the parents dont have twins (can't really calculate I think), it would be comparing to the General Population where incidence is 1/1000. I would go with D) 4% I have no idea!
My answer is also 4%, but I didnīt used the general population incidence.
Since the concordance for this trait in DZ twins is 0.04, this should also be for a future child...so I multiplied 0.04*100%...
 The above post was thanked by: Claus_CU (05-28-2011)

#4
05-28-2011
 USMLE Forums Veteran Steps History: Not yet Posts: 219 Threads: 18 Thanked 159 Times in 81 Posts Reputation: 158

Quote:
 Originally Posted by bebix My answer is also 4%, but I didnīt used the general population incidence. Since the concordance for this trait in DZ twins is 0.04, this should also be for a future child...so I multiplied 0.04*100%...
Exactly what I did, however i'm still not sure abt the answer..
#5
05-28-2011
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,357 Threads: 194 Thanked 3,268 Times in 881 Posts Reputation: 3278

Quote:
 Originally Posted by Amenah A male new born at 39 wks gestation has a unilateral cleft lip and palate. studies shown that concordance for this trait in MZ twins 0.40 and DZ twins 0.04. the incidence of cleft lip and palate in general population is 0.001 if the parents of this newborn have a second child the risk for unilateral cleft lip and palate in this child is approximately which? A)75% B)50% C)25% D)4% E)0% hi guys iv got this Q and i need ur help in approaching the correct answer
are we close?
#6
05-28-2011
 USMLE Forums Addict Steps History: 1+CK+CS Posts: 160 Threads: 15 Thanked 77 Times in 57 Posts Reputation: 88

hi guys ...thanks ....i took this question from kaplan q bank and the correct one is 4% ...u r totally correct ,i read the explanation but i didn't get how to approach the correct answer!!!
so we assume that the child would be DZ and we took 100% the general population and multiply 0.04 by 100% ...right?
thanks again
#7
05-28-2011
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,357 Threads: 194 Thanked 3,268 Times in 881 Posts Reputation: 3278

Quote:
 Originally Posted by Amenah hi guys ...thanks ....i took this question from kaplan q bank and the correct one is 4% ...u r totally correct ,i read the explanation but i didn't get how to approach the correct answer!!! so we assume that the child would be DZ and we took 100% the general population and multiply 0.04 by 100% ...right? thanks again
Yes..."genetically speaking", DZ twin are "just" two different sibling
 The above post was thanked by: Amenah (05-28-2011)
#8
05-28-2011
 USMLE Forums Addict Steps History: 1+CK+CS Posts: 160 Threads: 15 Thanked 77 Times in 57 Posts Reputation: 88

Quote:
 Originally Posted by bebix Yes..."genetically speaking", DZ twin are "just" two different sibling
Okay can i know why we didn't use the incidence which is 0.001 and we assume 100% for the general population. thank you again
#9
05-28-2011
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,357 Threads: 194 Thanked 3,268 Times in 881 Posts Reputation: 3278

Quote:
 Originally Posted by Amenah Okay can i know why we didn't use the incidence which is 0.001 and we assume 100% for the general population. thank you again
100% is not the general population...100% is just to convert 0.04 to percent.
I didnīt use the general population incidence of 1/1000, because this qs. is about a particular family which already have a child with unilateral cleft lip.
#10
05-28-2011
 USMLE Forums Addict Steps History: 1+CK+CS Posts: 160 Threads: 15 Thanked 77 Times in 57 Posts Reputation: 88

Quote:
 Originally Posted by bebix 100% is not the general population...100% is just to convert 0.04 to percent. I didnīt use the general population incidence of 1/1000, because this qs. is about a particular family which already have a child with unilateral cleft lip.
ha Okay i got it ,we just assume it's a DZ and pick the 4% ...thanks Bebix .
#11
05-28-2011
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,357 Threads: 194 Thanked 3,268 Times in 881 Posts Reputation: 3278

Quote:
 Originally Posted by Amenah ha Okay i got it ,we just assume it's a DZ and pick the 4% ...thanks Bebix .
Yes, in this particular question weīre assuming that the risk does not change if you are a DZ twin or a singleton.
The risk within the pair of DZ twin should be equal to the risk between two brothers.
 The above post was thanked by: Claus_CU (05-28-2011)
#12
05-28-2011
 USMLE Forums Veteran Steps History: Not yet Posts: 219 Threads: 18 Thanked 159 Times in 81 Posts Reputation: 158

Wow. You guys are seriously good with genetics.

 Tags Genetics-, Step-1-Questions

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