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  #1  
Old 06-09-2011
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DNA ∆F508 mutation for CF means...

Being identified as a carrier of the ∆F508 mutation for cystic fibrosis (OMIM 261600) means that:

A. An individual is likely to have Asian ancestry.
B. Clinical manifestations of CF will not occur.
C. A spouse should be studied for changes in the CF gene.
D. A sweat chloride test will be normal.
E. An individual has a 25% chance of having a child who is a carrier.
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  #2  
Old 06-09-2011
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i will go with C...
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Since CF is autosomal recessive, I'm between B and D.

I'd guess D, normal sweat chloride
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Old 06-09-2011
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i think C:sorry:
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Old 06-09-2011
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it is D i think..
Because cystic fibrosis is Autosomal recessive..
Even in pts with cystic fibrosis ,sometimes the sweat test is normal and we have to see transepithelial potential difference..(showing decreased secretion of Cl and increased resorption of H20 and Na+..
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Old 06-09-2011
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i wud go with E
reference...goljan pathology third edition page eighty two
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Old 06-09-2011
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i'm leaning towards b
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tough question bebix (i really like ur posts)
i think its B
and the D answer i think wrong coz when some is recessive it doesnt mean everything is normal same as sickle cell ..u have some sickled cells but u still without the manifestation of the disease
so i think D is gonna be somewhat abnormal but not diagnostic
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Old 06-10-2011
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B , the rest all seem to have some sort of tricky conditions to be true.
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Correct Answer correct answer

The answer is C.

Excluding common mutations does not guarantee that a rare mutation will not be present in one’s spouse. In addition, being identified as a “carrier for ∆F508” does not indicate that compound heterozygosity for it and a rare, alternative, mutation might not be present, and thus the spouse should be tested.

The ∆F508 mutation, the most common, is more frequent in northern Europeans, not Asians (choice A).
Compound heterozygotes for CF mutations may have unpredictable manifestations or age of onset (choice B).
The sweat chloride test will be normal only if the individual is not a compound heterozygote (choice D).
Any child of such an individual has a 50% chance of inheriting the gene with the ∆F508 mutation (choice E).

This question is from USMLE Roadmap Genetics
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  #11  
Old 06-10-2011
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thank y bebix!good questions
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Old 06-10-2011
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Can you explain what a compound heterozygote is?
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Star Compound heterozygotes

Inautosomal recessive inheritance, affected individuals who have the same mutation in each copy of the affected gene are known as homozygotes; those with a different mutation in each copy of the gene are compound heterozygotes.

In this particular case, the responsible gene is the cystic fibrosis transmembrane regulator (CFTR) on chromosome 7, and the most frequent mutation is loss of the entire codon for phenylalanine at position 508 (ΔF508). But unlike other AR (e.g. sickle cell disease, where all affected individuals have the same mutation), CF has a wide range of underlying mutations and compound heterozygotes are common.
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  #14  
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Thanks for the explanation!

I remember learning that there are many mutations that caused CF but over time I had forgotten that and only associated the F508 mutation with CF.

Good Question!
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