Biology of factor XI

Abstract

Unique among coagulation factors, the coagulation factor (F) XI arose through a duplication of the gene KLKB1 that encodes for plasma prekallikrein. This evolutionary origin sets FXI apart structurally as it is a homodimer with two identical subunits comprised of 4 apple and 1 catalytic domain. Each domain exhibits unique affinities for binding partners within the coagulation cascade, regulating the conversion of FXI to a serine protease as well as the selectivity of substrates cleaved by the active form of FXI. Beyond serving as the molecular nexus for the extrinsic and contact pathways to propagate thrombin generation by way of activating FIX, the function of FXI extends to contribute to barrier function, platelet activation, inflammation, and the immune response. Herein we critically review the current understanding of the molecular biology of FXI, touching on some functional consequences at the cell, tissue, and organ level. We conclude each section by highlighting the DNA mutations within each domain that present as FXI deficiency. Together, a narrative review of the structure-function of the domains of FXI is imperative to understand the etiology of Hemophilia C as well as identify regions of FXI to safely inhibit the pathological function of activation or activity of FXI without compromising the physiologic role of FXI.

Rare inherited coagulation disorders: no longer orphan and neglected

“…FXI deficiency is characterized by both homozygous (1 in 10 6 ) and heterozygous (1 in 30,000) inheritance patterns [ 72 , 73 ]. Unprovoked bleeding is rare, and bleeding is more likely to occur after dental, oropharyngeal, or urogenital surgery, ie, in tissues with high fibrinolytic activity, but even individuals with low plasma FXI often remain asymptomatic, so regular prophylaxis is very seldom needed [ 73 ].…”

“…Alternatively, a combination of FFP or SD-FFP (15-25 mL/kg) and tranexamic acid (15-20 mg/kg) may be considered ( Table 3 ) [ 8 ]. Low-dose rFVIIa (15-20 μg/kg) is safe and effective for perioperative management of FXI-deficient patients who develop FXI inhibitory alloantibodies [ 72 ].…”