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Old 07-26-2014
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Default Gaucher disease

A married couple is screened to assess the risk for Gaucher disease in their children. The activities of glucocerebrosidase in the sera of the mother and father are 45% and 55%, respectively, of the reference value. The couple has one child. Which of the following is the probability of the child possessing one or more alleles of the Gaucher mutation?

(A) 0
(B) 0.25
(C) 0.5
(D) 0.75
(E) 1.0
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B
Not sure
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Quote:
Originally Posted by Dr.ann View Post
B
Not sure
Good try Dr.ann.
However it would be useful if everyone can briefly explain how they arrived at the answer. This will help everyone to develop a thought process & learn.
We had a wonderful discussion for Step 2 CK & CS here which benefited us all.
Doesn't matter if our answer is wrong since I think it's better to be wrong here and learn from our mistakes than the actual test when it's already too late to learn.
Hope I am making sense.
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Yes u are right we should discuss Qs.. Thanks for the Qs plz do share more
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Old 07-26-2014
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Micrograph showing crinkled paper macrophages in the marrow space in a case of Gaucher disease. H&E stain.
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Old 07-26-2014
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Gaucher's dz has a autosomal recessive inheritance, therefore carrier state and homozygous mutated state are both possible genotypes for the child in question.

both the mother and father have 45% and 55% functionality of glucoceribrosidase enzyme, therefore I am going to assume assume that they are both homozygous for the mutation ( are are still living, so the disease phenotype shouldn't be too severe).

If both are homozygous, the child has a 100% chance of being homozygous for the mutation.

my answer is E....i know with Gaucher's, the phenotype varies even if both copies of the allele are mutated.
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What is the correct answer?
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D. 0.75 or 3/4

Gaucher's disease is AR.

According to the question stem, both mother and father have 45% and 55% level of enzyme activity in their blood making them heterozygous carriers of the AR gene.

Now according to Punnett square, when both parents are carriers, 3 out of 4 of the offspring can have one or more of the alleles.

In other words:

1 out of 4 will be homozygous for the disease since one mutated gene is inherited from each parent.

1 out of 4 will be homozygous normal since both normal genes are inherited.

2 out of 4 will be heterozygous carriers with one abnormal gene.

3 out of 4 will have one or more alleles of the Gaucher mutation.
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can i ask for some clarification- with autosomal recessive diseases, the carriers ( heterozygous) can be symptomatic?

I thought this was only exhibited with autosomal dominant diseases, where the heterozygous carrier will show the disease with a lower severity.

lol, funny thing is, my original answer was 75%, but after thinking a bit more..I thought heterozygous carriers would be asymptomatic..lesson..always go with first instinct
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Originally Posted by USMLEgen View Post
can i ask for some clarification- with autosomal recessive diseases, the carriers ( heterozygous) can be symptomatic?

I thought this was only exhibited with autosomal dominant diseases, where the heterozygous carrier will show the disease with a lower severity.

lol, funny thing is, my original answer was 75%, but after thinking a bit more..I thought heterozygous carriers would be asymptomatic..lesson..always go with first instinct
They were never symptomatic for the disease. They were found to be heterozygous carriers based on glucocerebrosidase levels.

I agree--Never change your answer unless you clicked on the wrong choice by mistake.

But that was the whole idea of doing this question i.e. making mistakes here rather than the test.
.
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