Which statement correctly identifies Hemophilia B?

Which statement correctly identifies Hemophilia B?

• A. Factor VIII deficiency
• B. Factor IX deficiency
• C. Factor X deficiency
• D. Factor XI deficiency

Answer: (B)

Hemophilia B is caused by a deficiency of Factor IX, a vitamin K–dependent clotting factor in the intrinsic pathway. Without enough Factor IX, the tenase complex (Factor IXa with Factor VIIIa) can’t effectively activate Factor X, so thrombin generation and clot formation are impaired. This produces a bleeding tendency with a prolonged aPTT while the PT tends to be normal, reflecting that the extrinsic pathway is unaffected. The condition is classically X‑linked recessive, mainly affecting males. Factor VIII deficiency causes Hemophilia A, which presents similarly but is due to Factor VIII deficiency. A deficiency of Factor X would disrupt the common pathway and typically prolong both PT and aPTT. Factor XI deficiency (Hemophilia C) is autosomal recessive and usually milder with variable bleeding. Thus, the statement describing a deficiency of Factor IX identifies Hemophilia B.

Hemophilia B is caused by a deficiency of Factor IX, a vitamin K–dependent clotting factor in the intrinsic pathway. Without enough Factor IX, the tenase complex (Factor IXa with Factor VIIIa) can’t effectively activate Factor X, so thrombin generation and clot formation are impaired. This produces a bleeding tendency with a prolonged aPTT while the PT tends to be normal, reflecting that the extrinsic pathway is unaffected. The condition is classically X‑linked recessive, mainly affecting males.

Factor VIII deficiency causes Hemophilia A, which presents similarly but is due to Factor VIII deficiency. A deficiency of Factor X would disrupt the common pathway and typically prolong both PT and aPTT. Factor XI deficiency (Hemophilia C) is autosomal recessive and usually milder with variable bleeding.

Thus, the statement describing a deficiency of Factor IX identifies Hemophilia B.