WBR0254

Author	PageAuthor::William J Gibson
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Biochemistry, MainCategory::Genetics
Sub Category	SubCategory::Hematology
Prompt	[[Prompt::A 16 year old male with cystic acne presents to his dermatologist after noting several large bruises spread across his body. The patient denies any history of trauma and cannot recall any previous history of easy bruising. He has been maintained on isotretinoin and clindamycin for the past six months without incident. The mechanism of the most likely clotting abnormality in this patient is most similar to which of the following bleeding conditions?]]
Answer A	AnswerA::Factor V Leiden
Answer A Explanation	[[AnswerAExp::Incorrect: Factor V can be mutated to a prothrombotic isoform termed Factor V Leiden. This is the most common cause of hereditary prothrombotic syndrome. The Factor V Leiden mutation produces a gene product that cannot be degraded by protein C, resulting in increased Factor V levels. The vitamin K deficiency of this patient results in decreased coagulability by decreasing the levels of coagulation factors 2,7,9,,10 as well as protein C and S.]]
Answer B	AnswerB::Glanzman’s Thrombosthenia
Answer B Explanation	AnswerBExp::'''Incorrect:''' While Glanzman’s thrombosthenia may cause increased bleeding, it is an abnormality of platelet function and not the coagulation cascade (like vitamin K deficiency).
Answer C	AnswerC::Hemophilia A
Answer C Explanation	AnswerCExp::'''Correct:''' Hemophilia A is caused by a deficiency of Factor IX. This factor is also decreased in Vitamin K Deficiency.
Answer D	AnswerD::Thrombotic Thrombocytopenic Purpura
Answer D Explanation	AnswerDExp::'''Incorrect:''' Thrombotic Thrombocytopenic Purpura is primarily a disorder affecting platelet function.
Answer E	AnswerE::Protein C deficiency
Answer E Explanation	AnswerEExp::'''Incorrect:''' While Protein C is decreased by vitamin K deficiency, the main symptom of vitamin K deficiency is a decrease in coabulability. Pure protein C deficiency causes hyper coagulability.
Right Answer	RightAnswer::C
Explanation	[[Explanation:: Educational Objective: References: ]]
Approved	Approved::Yes
Keyword	WBRKeyword::Vitamin K, WBRKeyword::Hemophilia, WBRKeyword::Haemophilia, WBRKeyword::Bruising, WBRKeyword::Bleed, WBRKeyword::Bleeding, WBRKeyword::Coagulation
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