Hemophilia B is due to deficiency of-
**Core Concept**
Hemophilia B, also known as Christmas disease, is a rare genetic disorder caused by a deficiency of a specific clotting factor. This deficiency leads to impaired blood coagulation, resulting in prolonged bleeding episodes.
**Why the Correct Answer is Right**
Hemophilia B is caused by a deficiency of the clotting factor IX, also known as Christmas factor. This factor plays a crucial role in the intrinsic pathway of blood coagulation, where it helps to activate factor X to factor Xa. Without sufficient factor IX, the coagulation cascade is disrupted, leading to bleeding complications. The deficiency of factor IX is usually due to a mutation in the F9 gene, which encodes for the factor IX protein.
**Why Each Wrong Option is Incorrect**
**Option A:** Factor VIII is actually the clotting factor deficient in Hemophilia A, not Hemophilia B.
**Option B:** Factor XIII is a clotting factor involved in stabilizing fibrin clots, but its deficiency does not cause Hemophilia B.
**Option C:** Factor VII is a clotting factor involved in the extrinsic pathway of blood coagulation, and its deficiency is associated with bleeding disorders other than Hemophilia B.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that Hemophilia B is an X-linked recessive disorder, meaning it primarily affects males. However, females can be carriers of the disease and may exhibit mild symptoms.
**Correct Answer: D. Factor IX.**