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Old 10-14-2012
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Question Female with Hemophilia A

An 8-year-old girl is brought to the emergency department after experiencing sudden severe dyspnea. On examination, she has upper airway obstruction from soft tissue swelling in her neck. A radiograph shows a hematoma compressing the trachea. Laboratory studies show her prothrombin time is normal, but her partial thromboplastin time is increased. Further testing reveals less than 1% of normal factor VIII level. Both parents and two female siblings are unaffected by this problem, but a male sibling has experienced a similar episode. Which of the following genetic abnormalities is most likely to account for the findings in this girl ?

A Autosomal dominant mutation
B Autosomal recessive mutation
C Genomic imprinting
D Germline mosaicism
E Random X inactivation
F Spontaneous new mutation
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Old 10-14-2012
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E Random X inactivation i think ...........................
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Old 10-14-2012
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E
Random x inactivation..( lyonization)
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Old 10-14-2012
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Random X inactivation
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Old 10-15-2012
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Default manifesting heterozygote

This girl has features of hemophilia A. This X-linked recessive condition is expected to occur in males, however, who inherit the one maternal X chromosome with the genetic mutation, and they do not have another X chromosome with a normal functional allele, as is the case in her brother. Hemophilia in a female can be explained by the Lyon hypothesis,
which states that only one X chromosome in a female is active (the “turned off” X chromosome is the Barr body) for most genes, but this inactivation is a random event. Some individuals are out on the tail end of the Poisson distribution of random events and have few active X chromosomes with the normal allele, leading to markedly diminished factor VIII levels.
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Old 10-15-2012
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E Random X inactivation
I think carrier daughter normal X got inactivated and she got affected.
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Old 10-15-2012
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The answer is E ..... She's a manifesting heterozygote, but still how can she have the same symptoms as her brother. I thought females displaying symptoms of an X linked disorder should have milder manifestions than their male counterparts due to the fact that they still carry chromosomes with the normal allele in their cells
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