Hemophilia B is characterized by a defect in which clotting factor?

• A. Clotting factor VIII
• B. Clotting factor X
• C. Clotting factor IX
• D. Dystrophin

Answer: (C)

Hemophilia B is specifically caused by a deficiency in clotting factor IX. This genetic disorder is inherited in an X-linked recessive manner, which primarily affects males. When there’s a mutation or deficiency in the gene responsible for producing factor IX, the coagulation cascade is disrupted, leading to impaired blood clotting. As a result, individuals with hemophilia B experience prolonged bleeding episodes and have a higher risk of spontaneous bleeds.

In contrast, clotting factor VIII is associated with Hemophilia A, which is a different condition. Clotting factor X plays a role in the common pathway of the coagulation cascade but is not deficient in Hemophilia B. Dystrophin, meanwhile, is a protein associated with muscular dystrophy and is unrelated to blood clotting factors. Understanding the specific role of each clotting factor helps clarify why factor IX deficiency is central to diagnosing and understanding hemophilia B.