WBR0255

Author	PageAuthor::William J Gibson
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Biochemistry, MainCategory::Genetics
Sub Category	SubCategory::Hematology
Prompt	[[Prompt::A newborn male is born to a gravida 1 para 1 33 year old woman by normal vaginal delivery. The woman received proper prenatal care including folic acid supplementation. The child undergoes circumcision, but his bleeding does not cease for 4 hours. The physician orders laboratory testing which reveals: Increased PTT, normal PT, and platelets of 235,000. Further evaluation demonstrates Factor VIII activity 4% of normal. What is the mode of inheritance of the most likely condition?]]
Answer A	AnswerA::Autosomal recessive
Answer A Explanation	AnswerAExp::Hemophilia A is not an autosomal recessive disorder. An example of an autosomal recessive disease is phenylketonuria.
Answer B	AnswerB::Autosomal dominant
Answer B Explanation	AnswerBExp::Hemophilia A is not an autosomal dominant disorder. An example of an autosomal dominant disorder is von Willebrand disease.
Answer C	AnswerC::X-linked dominant
Answer C Explanation	AnswerCExp::Hemophilia is not an X-linked dominant disorder. An example of an X-linked dominant disorder is Rett syndrome.
Answer D	AnswerD::X-linked recessive
Answer D Explanation	AnswerDExp::One of the first sign of Hemophilia can be abnormally prolonged bleeding following circumcision. Hemophilia A is an X-linked recessive disorder.
Answer E	AnswerE::Mitochondrial
Answer E Explanation	AnswerEExp::Hemophilia A is not a mitochondrial disorder. An example of a mitochondrial disorder is Leber’s hereditary optic neuropathy.
Right Answer	RightAnswer::D
Explanation	[[Explanation::The patient in this vignette has Hemophilia A, an X-linked recessive bleeding disorder caused by a deficiency of Factor VIII. Factor VIII normally functions to promote the function of the intrinsic coagulation cascade and cause fibrin cross-linked clots to form. One of the earliest signs of hemophilia can be abnormally long bleeding following circumcision. In both Hemophilia A and B, spontaneous bleeding is common. On laboratory testing, these patients have a normal bleeding time, normal prothrombin time, normal thrombin time, but prolonged partial thromboplastin time. The most characteristic type of internal bleed is a joint bleed where blood enters into the joint spaces. Bleeding can be controlled with regular infusions of the deficient clotting factor, i.e. factor VIII in Hemophilia A or factor IX in Hemophilia B. Educational Objective: Hemophilia A is an X-linked recessive disease. References: First Aid 2012 page 389]]
Approved	Approved::Yes
Keyword	WBRKeyword::Blood, WBRKeyword::Bleeding, WBRKeyword::Circumcision, WBRKeyword::Hemophilia, WBRKeyword::X-linked, WBRKeyword::X-linked recessive, WBRKeyword::Coagulation
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