WBR0080
| Author | PageAuthor::William J Gibson |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Genetics |
| Sub Category | SubCategory::Hematology |
| Prompt | [[Prompt::A 5 year old boy is brought to the emergency room by his parents following severe bleeding after a fall. Approximately 12 hours to presentation, the boy hit his knee on a table in his room when jumping off of his bed. Since then, his knee has swollen severely. The knee is tender to palpation and elicits pain with both active and passive flexion. Laboratory testing reveals the following: PT: 13 seconds (normal: 11-15), PTT: 65 seconds (normal: 25-40 seconds), Platelet count: 250,000 (normal: 150,000-400,000). The patient is infused with cryoprecipitate and his bleeding resolves. Which of the following proteins is most likely deficient in this patient?]] |
| Answer A | AnswerA::GpIb |
| Answer A Explanation | [[AnswerAExp::GPIb is deficient in Bernard-Soulier disease]] |
| Answer B | AnswerB::Factor V |
| Answer B Explanation | [[AnswerBExp::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.]] |
| Answer C | AnswerC::Factor VIII |
| Answer C Explanation | [[AnswerCExp::Factor VIII deficiency is responsible for Hemophilia A. Hemophilia Type A (80%) is more common than Hemophilia B (20%).]] |
| Answer D | AnswerD::Factor IX |
| Answer D Explanation | AnswerDExp::Factor XI deficiency is responsible for Hemophilia B. |
| Answer E | AnswerE::von Willebrand Factor (vWF) |
| Answer E Explanation | [[AnswerEExp::vWF deficiency causes von Willebrand’s disease, the most common bleeding disease. In contrast to hemophilia, von Willebrand’s disease is a mixed coagulation and platelet dysfunction disorder. Patients typically experience cutaneous and mucosal bleeding. von Willebrand’s disease can be treated with desmopressin, which releases stored vWF from the endothelium. von Willebrand Disease is inherited in an autosomal dominant fashion.]] |
| Right Answer | RightAnswer::C |
| Explanation | [[Explanation::The patient in this vignette has Hemophilia, as evidenced by his excessive joint bleeding and elevated PTT. Hemophilia is an X-linked recessive bleeding disorder caused by deficiency of certain clotting factors. Hemophilia A (80% of cases) is caused by deficiency of Factor VIII, and Hemophilia B (20% of cases) is caused by deficiency of Factor IX.
In both haemophilia 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 haemophilia A or factor IX in haemophilia B. One complication of factor supplementation is resistance; some patients may develop antibodies to the administered clotting factors. In milder forms of Hemophilia A, DDAVP can be used. DDAVP causes endothelial cells to release vW. The newly released vWF binds to and stabilizes Factor VIII, thereby increasing its half life in serum. |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Hemophilia, WBRKeyword::Haemophilia, WBRKeyword::Bleed, WBRKeyword::Bleeding, WBRKeyword::Blood, WBRKeyword::Coagulation |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |