The Phenotypic Expression of Homozygous and Compound Heterozygous Factor V R506Q (Factor V Leiden, FVL) and Factor II A20210G: Ten Years Experience At a Referral Center

Abstract 5252

Heterozygous Factor V Leiden, the most common inherited thrombotic disorder with an estimated incidence of about 5% in Caucasian population, poses a moderate risk of first venous thromboembolic (VTE) event. The homozygous and compound heterozygous states are comparatively rare but are thought to be associated with high risk of recurrent VTE. This report describes ten years experience with homozygous and compound heterozygous FVL and Factor II A20210G at a major referral center in central Pennsylvania, USA. Between January 2000 and December 2010, 31 homozygous F VL patients, 2 homozygous FII A20210G, 10 compound heterozygous FVL and F II A20210G and 6 compound heterozygous F VL and protein C (PC), protein S (PS) or antithrombin (AT) deficiency were encountered. The reasons for referral were personal or family history of VTE or a first degree relative diagnosed with any of these conditions. Among these patients, 5 homozygous F VL, 1 compound heterozygous F VL and F II A20210G, and 1 compound heterozygous factor VL and PC deficiency remained free of VTE at age 17–64 years, even though they were exposed to prothrombotic conditions, e.g., surgery, hormones or pregnancy. Two compound heterozygous F VL and PS deficient patients suffered ischemic strokes, one at age 3 ½ years and the other at age 45 years, but no VTE. The other patients suffered lower extremity deep vein thrombosis and/or pulmonary embolism or visceral thrombosis. Most had recurrent events. Our experience highlights the serious thrombotic risks associated with homozygous and compound heterozygous F VL and F II A20210G status but also indicates that some patients remain thrombosis free despite exposure to additional prothrombotic conditions. However, because of referral bias this series of patients may not truly reflect the overall occurrence of VTE in patients with homozygous or compound heterozygous inherited thrombophilia.