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Abstract
Factor IX:C (FIX:C) levels vary in hemophilia B carriers even in pedigrees with a
unifying genetic defect. Analyzing the balance between pro-and anticoagulants might
increase our understanding of carriers’ bleeding potential. In this research study,
we evaluated bleeding scores (BS) and a novel mathematical model of thrombin generation
(TG) in Amish FIX:C deficient carriers and controls. Blood samples and BS were obtained
from post-menarchal females, including 59 carriers and 57 controls from the same extended
pedigree. Factors II, V, VII, VIII, IX, X, antithrombin, tissue factor pathway inhibitor
and protein C were assayed to generate mathematical models of TG in response to 5pM
tissue factor (TF) and for TF + thrombomodulin. BS was based on a modification of
the MCMDM-1VWD scoring system. Carriers had a lower mean FIX:C (68% vs. 119%), von
Willebrand factor antigen (108 vs.133) and Tissue activatable fibrinolysis inhibitor
(103 vs. 111) compared to controls; both groups had a similar mean BS. Carriers demonstrated
significantly lower TG parameters on both mathematical models compared to controls.
Carriers with FIX:C ≤ 50% had lower TG curves than those > 50% but similar BS. Thrombin
generation showed significant differences between carriers and controls, between low
(≤50%) and high (> 50%) FIX:C carriers, and specifically in the TF + thrombomodulin
model, between high FIX:C carriers and controls, although the BS were not different.