Genetic determinants of normal variation in coagulation factor (F) IX levels: genome‐wide scan and examination of the FIX structural gene

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