What is the role of factor IX inhibitors in the etiology of factor IX deficiency (FIX) (hemophilia B)?

Updated: Mar 09, 2021
  • Author: Robert A Schwartz, MD, MPH; Chief Editor: Srikanth Nagalla, MD, MS, FACP  more...
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Answer

FIX gene deletions are present in 50% of patients with FIX inhibitors. In contrast, the risk of inhibitor development is 20% in patients with mutations resulting in loss of coding information.

A study of eight alloantibodies to FIX that developed after repeated infusions of FIX in patients with hemophilia B showed that the antibodies were immunoglobulin G (IgG), predominantly IgG subclass 1 and IgG subclass 4. They were directed against the Gla and protease domains and inhibited binding of FIX to phospholipids and binding of the light chain of FVIIIa to FIXa. They also inhibited the FVIIIa-dependent activation of FX. [16]


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