156 q 2001 Blackwell Science Ltd SHORT REPORT High factor VIII antigen levels increase the risk of venous thrombosis but are not associated with polymorphisms in the von Willebrand factor and factor VIII gene Pieter W. Kamphuisen, 1 Jeroen C. J. Eikenboom, 1 Frits R. Rosendaal, 1,2 Ted Koster, 2 Andrew D. Blann, 3 Hans L. Vos 1 and Rogier M. Bertina 1 1 Haemostasis and Thrombosis Research Centre and 2 Department of Clinical Epidemiology, Leiden University Medical Centre, Leiden, and 3 Thrombosis, Haemostasis and Vascular Biology Unit, University Department of Medicine, The City Hospital, Birmingham, UK Received 18 January 2001; accepted for publication 19 June 2001 Summary. High factor VIII levels increase the risk of venous thromboembolism, but the mechanisms that cause high factor VIII levels are unclear. In 301 thrombosis patients and 301 matched healthy controls, factor VIII antigen (VIII:Ag) levels $ 150 IU/dl increased the thrombosis risk more than fivefold. We investigated whether high factor VIII:Ag levels result from a genetic variation in the factor VIII or von Willebrand factor (VWF) genes. Six polymorphisms in the VWF gene and two CA-repeats in the factor VIII gene were not associated with plasma VWF levels, factor VIII:Ag levels, or thrombosis risk. Our data do not support the hypothesis that a single functional sequence variation in the factor VIII or VWF gene explains the majority of high factor VIII levels and thrombotic risk. Keywords: factor VIII, von Willebrand factor, venous thrombosis, polymorphisms. High factor VIII coagulant activity (factor VIII:C) levels are associated with an increased risk of deep vein thrombosis (Koster et al, 1995; Kraaijenhagen et al, 2000; Kyrle et al, 2000). The relative risk associated with levels $ 150 IU/dl was 4´8 (95% CI 2´3±10´0) compared with levels , 100 IU/dl (Koster et al, 1995). The prevalence of such high factor VIII:C levels is 25% in thrombosis patients and 11% in healthy control subjects (Koster et al, 1995). The mechanisms that lead to high plasma factor VIII levels are unclear. Von Willebrand factor (VWF), as carrier protein of factor VIII, is an important determinant of the factor VIII level (Wise et al, 1991). Previously, we reported familial clustering for factor VIII:C and VWF antigen (VWF:Ag) levels, even after adjustment for blood group (Kamphuisen et al, 1998). This strongly suggests the existence of additional genetic components controlling both VWF and factor VIII levels. In the present study, we investigated whether high factor VIII levels are associated with a single common variation in the factor VIII or VWF gene, and whether this variation is associated with an increased thrombosis risk. PATIENTS AND METHODS We studied 301 patients and 301 age-matched controls from the Leiden Thrombophilia Study (LETS) (Koster et al, 1995). Factor VIII:C and VWF:Ag levels were measured using a one-stage clotting assay (Koster et al, 1995) and an enzyme-linked immunosorbent assay (ELISA) (Blann et al, 1995) respectively. Factor VIII antigen (VIII:Ag) was measured using a sandwich-type ELISA with two mono- clonal antibodies directed against different epitopes on the light chain of factor VIII. Two CA-dinucleotide repeat polymorphisms within intron 13 (Lalloz et al, 1991) and intron 22 (Lalloz et al, 1994) of the factor VIII gene were analysed. We studied six single nucleotide polymorphisms in the VWF gene: four poly- morphisms in the promoter region of the VWF gene (Zhang et al, 1994) (21793C/G, 21234C/T, 21185 A/G and 21051G/A) and two polymorphisms in the region coding for the factor VIII-binding domain [2365A/G (Thr/Ala 789; exon 18) and 2555G/A (Arg/Gln 852; exon 20)]. Linear regression was used for comparisons between British Journal of Haematology , 2001, 115, 156±158 Correspondence: Rogier M. Bertina, Haemostasis and Thrombosis Research Centre, Leiden University Medical Centre, C2-R, PO Box 9600, 2300 RC Leiden, The Netherlands. E-mail: r.m.bertina@ lumc.nl