title: VKORC1 mutations detected in patients resistant to vitamin K antagonists are not all associated with a resistant VKOR activity.
abstract: BACKGROUND
  The VKORC1 gene codes for the VKORC1 enzyme, which is responsible for the reduction of vitamin K epoxide into vitamin K. VKORC1 enzyme is the target of vitamin K antagonists (VKA). Twenty-eight rare single mutations in the VKORC1 coding sequence have been reported from resistant patients receiving unusually high doses of VKA to achieve therapeutic anticoagulation.
  
  
  OBJECTIVE
  It has been suggested that these mutations are responsible for the resistant phenotype, while biochemical consequences of these mutations on the VKORC1 enzyme have not yet been evaluated. Therefore, the aim of this study was to investigate the causality of the VKORC1 mutations in the resistance phenotype.
  
  
  METHODS
  Wild-type VKORC1 and its spontaneous mutants were expressed in Pichia pastoris and susceptibility to VKA was assessed by the in vitro determination of kinetic and inhibition constants.
  
  
  CONCLUSIONS
  The in vitro analysis revealed that six mutations only (A26P, A41S, V54L, H68Y, I123N and Y139H) were associated with increase in K(i) , suggesting their involvement in the resistance phenotype observed in patients. A41S and H68Y led to selective resistance, respectively, to indane-1,3-dione and 4-hydroxycoumarine derivatives. The other mutations did not increase the K(i). Furthermore, 10 mutations (S52L, S52W, W59L, W59R, V66M, V66G, G71A, N77S, N77T and L128R) led to an almost complete loss of activity. These results suggest the existence of other resistance mechanisms.
authors.affiliation: USC 1233 INRA-Vetagro Sup, Veterinary School of Lyon, 69280 Marcy l'Etoile, France.
authors.forename: A
authors.initials: A
authors.lastname: Hodroge
authors.forename: B
authors.initials: B
authors.lastname: Matagrin
authors.forename: C
authors.initials: C
authors.lastname: Moreau
authors.forename: I
authors.initials: I
authors.lastname: Fourel
authors.forename: A
authors.initials: A
authors.lastname: Hammed
authors.forename: E
authors.initials: E
authors.lastname: Benoit
authors.forename: V
authors.initials: V
authors.lastname: Lattard
mesh_terms: D015153:Blotting, Western; D006801:Humans; D006899:Mixed Function Oxygenases / Q000235:genetics*; D009154:Mutation; D014812:Vitamin K / Q000037:antagonists & inhibitors*; D064417:Vitamin K Epoxide Reductases
chemical_list: D014812:Vitamin K; D006899:Mixed Function Oxygenases; C578523:VKORC1 protein, human; D064417:Vitamin K Epoxide Reductases