Though hemophilia A and B are traditionally considered clinically indistinguishable, a study published in Blood Transfusion suggests that severe hemophilia B (factor IX deficiency) may be clinically less severe than hemophilia A (factor VIII deficiency), emphasizing a need to discuss further therapeutic options for each disorder.
The authors reviewed published studies to support this claim, determining that hemophilia B was milder than hemophilia A based on the following findings:
- Hemophilia B was associated with less-severe gene mutations: Null mutations, which are associated with a more severe clinical phenotype in severe hemophilia, are more prevalent in severe hemophilia A (~80%) than in severe hemophilia B (~60%).
- Hemophilia B was associated with less-severe clinical symptoms: The hemophilia severity score is higher in patients with severe hemophilia A than in those with severe hemophilia B. This was based on evidence from a large Canadian study showing that patients with severe hemophilia B bled less frequently than patients with hemophilia A, and an Italian study demonstrating that patients with hemophilia B had fewer hemarthroses and lower World Federation of Hemophilia ultrasound scores.
- Patients with hemophilia B have less factor consumption: A clinical trial investigating long-acting factor VIII and factor IX products found that the rate of bleeding episodes during the 12 months prior to study enrollment was markedly lower in hemophilia B patients. There is also evidence to suggest that patients with hemophilia B use less replacement therapy annually compared with patients with hemophilia A.
“All in all, although the evidence presented here is not conclusive, there is a hint that severe hemophilia B may be clinically less severe than hemophilia A,” the researchers concluded. “These findings raise the question of when and at which dosages and intervals should prophylaxis be recommended to patients with severe FIX deficiency.”
Source: Franchini M and Mannucci PM. Haemophilia B is clinically less severe than haemophilia A: further evidence. Blood Transfus. 2016 October 4. [Epub ahead of print]