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::'''Incorrect:''' 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::'''Incorrect:''' 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::'''Incorrect:''' 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::'''Correct:''' 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::'''Incorrect:''' 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 387. |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::Blood, WBRKeyword::Bleeding, WBRKeyword::Circumcision, WBRKeyword::Hemophilia, WBRKeyword::X-linked, WBRKeyword::X-linked recessive, WBRKeyword::Coagulation |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |