Haemophilia B is due to mutation of gene corresponding to factor?
First, I need to recall the basics. Hemophilia A and B are both X-linked recessive disorders. Hemophilia A is due to Factor VIII deficiency, and Hemophilia B is Factor IX. But wait, I should double-check that. Sometimes people mix them up because they're both clotting factors.
The core concept here is the genetic basis of Hemophilia B. The key point is that Hemophilia B is caused by a mutation in the Factor IX gene. The gene for Factor IX is located on the X chromosome, which is why it's X-linked. This makes sense because males, having only one X chromosome, are more commonly affected, while females are typically carriers.
Now, the correct answer is Factor IX. The explanation should mention the gene location (Xq27.1-27.2) and the role of Factor IX in the intrinsic pathway of coagulation. It's important to note that Factor IX is a serine protease that activates Factor X, which is part of the common pathway.
For the incorrect options: Hemophilia A is Factor VIII. Von Willebrand disease is related to VWF, which affects Factor VIII stability. Factor XI deficiency is called Hemophilia C, which is autosomal and less severe. Factor X is part of the common pathway but not related to Hemophilia B.
The clinical pearl should emphasize the difference between A and B, maybe using a mnemonic like "A for Eight, B for Nine." Also, remember that treatment involves replacement therapy with the respective factors.
I need to structure the explanation with the required sections, making sure each part is concise and within the character limit. Avoid jargon where possible but use precise terminology for indexing. Check that each wrong option is clearly explained as incorrect. Make sure the correct answer line is at the end.
**Core Concept**
Hemophilia B is an X-linked recessive bleeding disorder caused by mutations in the **Factor IX** gene. This gene encodes a key clotting factor in the intrinsic pathway of coagulation, essential for activating Factor X during thrombin generation.
**Why the Correct Answer is Right**
Hemophilia B results from mutations in the **F9 gene** located on the X chromosome (Xq27.1-27.2). Factor IX is a vitamin K-dependent serine protease that binds calcium to activate Factor X, bridging the intrinsic and common coagulation pathways. Deficiency leads to prolonged activated partial thromboplastin time (aPTT) and impaired clot formation, causing spontaneous bleeding episodes.
**Why Each Wrong Option is Incorrect**
**Option A:** Factor VIII deficiency causes Hemophilia A (not B).
**Option C:** Factor XI deficiency causes Hemophilia C, an autosomal recessive disorder with milder symptoms.
**Option D:** Factor X deficiency is rare and not X-linked; it affects the common pathway but is unrelated to Hemophilia B.
**Clinical Pearl / High-Yield Fact**
Remember: **"A for Eight, B for Nine"** (Hemophilia A = Factor VIII, Hemophilia B = Factor IX). Hemophilia B is also known as Christmas disease, named after the first described patient. Always check aPT