title: Resequencing of VKORC1, CYP2C9 and CYP4F2 genes in Italian patients requiring extreme low and high warfarin doses.
abstract: OBJECTIVE
  The aim of the present study was to investigate the genetic variability of VKORC1, CYP2C9 and CYP4F2 genes in patients who required a very low and high warfarin dose, in order to identify novel variants that could help to explain the particular extreme dose requirements.
  
  
  METHODS
  Among patients followed and treated with warfarin at the Center of Haemostasis and Thrombosis of the PTV, we selected twelve patients showing a high divergence from warfarin standard doses required to achieve the therapeutic effect. All VKORC1, CYP2C9 and CYP4F2 coding regions, 3' and 5' UTR and exon/intron boundaries were analyzed by direct sequencing.
  
  
  RESULTS
  The 1173T and -1639A allele variants in VKORC1 gene, associated with warfarin sensitivity, were present, as expected, mostly in low dose patients while 3730A allele, linked to warfarin resistance, has been found only in high dose patients. Interestingly, we found that three out of six low dose subjects presented CYP2C9*3/*3 homozygous genotype, very rare in Caucasians. Besides these common polymorphisms, we identified 5 SNPs in CYP2C9 gene and 19 SNPs in CYP4F2 gene. Among these, all polymorphisms identified in CYP2C9 gene were present only in low dose patients and three of them resulted in linkage with CYP2C9*2 and CYP2C9*3. Regarding CYP4F2 SNPs, we did not observe differences between the high and low dose patients. At the end, the whole sequencing did not reveal any novel polymorphism/mutation.
  
  
  CONCLUSIONS
  Further studies are required to identify other genetic factors contributing to extreme warfarin requirement.
authors.affiliation: Department of Biomedicine and Prevention, Genetics Section, University of Rome Tor Vergata, Rome, Italy.
authors.forename: Davide
authors.initials: D
authors.lastname: Di Fusco
authors.forename: Cinzia
authors.initials: C
authors.lastname: Ciccacci
authors.forename: Sara
authors.initials: S
authors.lastname: Rufini
authors.forename: Vittorio
authors.initials: V
authors.lastname: Forte
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Novelli
authors.forename: Paola
authors.initials: P
authors.lastname: Borgiani
mesh_terms: D000925:Anticoagulants / Q000494:pharmacology / Q000627:therapeutic use*; D001189:Aryl Hydrocarbon Hydroxylases / Q000235:genetics*; D065729:Cytochrome P-450 CYP2C9; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics*; D000072470:Cytochrome P450 Family 4; D004305:Dose-Response Relationship, Drug; D004351:Drug Resistance / Q000235:genetics; D006801:Humans; D007558:Italy; D008661:Metabolism, Inborn Errors / Q000235:genetics*; D010597:Pharmacogenetics; D020641:Polymorphism, Single Nucleotide; D064417:Vitamin K Epoxide Reductases / Q000235:genetics*; D014859:Warfarin / Q000494:pharmacology / Q000627:therapeutic use*; D044465:White People / Q000235:genetics
chemical_list: D000925:Anticoagulants; D014859:Warfarin; D003577:Cytochrome P-450 Enzyme System; C450260:CYP2C9 protein, human; D065729:Cytochrome P-450 CYP2C9; D001189:Aryl Hydrocarbon Hydroxylases; D000072470:Cytochrome P450 Family 4; C117480:CYP4F2 protein, human; C578523:VKORC1 protein, human; D064417:Vitamin K Epoxide Reductases
keywords: CYP2C9; CYP4F2; Pharmacogenetics; Polymorphism; VKORC1; Warfarin