Relative risk of venous thromboembolism in first-degree family members of subjects with venous thromboembolism and factor V Arg → Gln506 mutation: S. Middeldorp1, M.M.W. Koopman1, C.M.A. Henkens2, L. van Pampus3, K. Hamulyák3, J. van der Meer2, M.H. Prins, H.R. Büller1. 1 Centrum voor Hemostase en Trombose, Academisch Medisch Centrum, Amsterdam, 2, Department of Haematology, University Hospital, Groningen, 3 Department of Haematology, University Hospital, Maastricht, Netherlands