Deficiency in factor IX is associated with which disorder?

• A. Hemophilia A
• B. Von Willebrand disease
• C. Hemophilia B
• D. Sickle cell disease

Answer: (C)

Deficiency in a specific coagulation factor points to a classic inherited bleeding disorder. When factor IX is missing or defective, the condition is Hemophilia B, also known as Christmas disease. In the coagulation cascade, factor IX is part of the intrinsic pathway that helps generate thrombin and stabilize clots. Without enough factor IX, thrombin production is reduced, leading to a tendency for deep tissue and joint bleeding and prolonged bleeding after injuries or surgeries. Lab clues often include a prolonged activated partial thromboplastin time (aPTT) with a normal prothrombin time (PT), reflecting the intrinsic pathway defect. Hemophilia B is X-linked and typically affects males.

By contrast, Hemophilia A is due to factor VIII deficiency, and Von Willebrand disease involves a deficiency or dysfunction of von Willebrand factor, which impairs platelet adhesion and function and often presents with mucocutaneous bleeding. Sickle cell disease is a hemoglobinopathy with vaso-occlusive symptoms, not a primary coagulation factor deficiency.