PURPOSE: ORM1 is a plasma drug binding protein. Its polymorphism rs17650 (S>F) 
has been reported to be an important factor affecting the binding ability and 
effect of antiretroviral protease inhibitors. The aim of this study was to 
determine whether the ORM1 rs17650 polymorphism also influences warfarin 
therapy.
METHODS: A total of 191 Chinese patients with steady-dose warfarin therapy were 
enrolled in this study. The patients were studied for warfarin maintenance dose, 
the ORM1 rs17650 polymorphism, and two polymorphisms previously demonstrated to 
affect warfarin response [CYP2C9 rs1057910 (3) and VKORC1 rs7294 (-1639 G>A)].
RESULTS: Warfarin dose was partially correlated with the VKORC1 rs7294, CYP2C9 
rs1057910 and ORM1 rs17650 polymorphisms. Patients carrying the wild-type of 
these three genes (n = 96) took a mean dose of 3.0 ± 1.1 mg warfarin, which was 
significantly higher than that taken by the 52 S patients (2.7 ± 0.7) and 11 S S 
patients (2.5 ± 0.6 mg) (p = 0.048).
CONCLUSION: We identified ORM1 as another polymorphic gene affecting warfarin 
dose requirements. ORM1 S carriers require lower maintenance doses to achieve 
and maintain an optimal level of anticoagulation.