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Updated: Aug 7, 2026

Measurement of Factor V Activity in Human Plasma Using a Microplate Coagulation Assay
Published on: September 9, 2012
Genetic determinants of normal variation in coagulation factor (F) IX levels: genome-wide scan and examination of the
M Khachidze1, A Buil, K R Viel
1Department of Pathology and Laboratory-Medicine, Emory University, 101 Woodruff Circle, Atlanta, GA 30322, USA.
Background:
High-normal and elevated plasma FIX activity (FIX:C) levels are associated with increased risk for venous- and possibly arterial-thrombosis.
Objective:
Because the broad normal range for FIX:C involves a substantial unknown genetic component, we sought to identify quantitative-trait loci (QTLs) for this medically important hemostasis trait.
Methods:
We performed a genome-wide screen and a resequencing-based variation scan of the known functional regions of every distinct FIX gene (F9) in the genetic analysis of idiopathic thrombophilia project (GAIT), a collection of 398 Spanish-Caucasians from 21 pedigrees.
Results:
We found no evidence for linkage (LOD scores <1.5) despite genotyping more than 540 uniformly-spaced microsatellites. We identified 27 candidate F9 polymorphisms, including three in cis-elements responsible for the increase in FIX:C that occurs with aging, but found no significant genotype-specific differences in mean FIX:C levels (P-values > or = 0.11) despite evaluating every polymorphism in GAIT by marginal multicovariate measured-genotype association analysis.
Conclusions:
The heritable component of interindividual FIX:C variability likely involves a collection of QTLs with modest effects that may reside in genes other than F9. Nevertheless, because the alleles of these 27 polymorphisms exhibited a low overall degree of linkage disequilibrium, we are currently defining their haplotypes to interrogate several highly-conserved non-exonic sequences and other F9 segments not examined here.
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