Warfarin is a widely prescribed anticoagulant for the prevention of thromboembolic diseases for subjects with deep vein thrombosis, atrial fibrillation, or mechanical heart valve replacement. The dose requirement is highly variable, both interindividually and interethnically. Variation in the VKORC1 gene is believed to be the most important individual predictor of warfarin dose, accounting for about 30% of the variance observed in dosing. [From OMIM]