title: Influence of APOE genotypes and VKORC1 haplotypes on warfarin dose requirements in Asian patients.
abstract: BACKGROUND
  Recent studies on pharmacogenetics of warfarin have implicated apolipoprotein E (APOE) polymorphisms to influence the vitamin K dependent coagulation cascade and hence the efficacy of warfarin. Studies among Caucasian and African Americans showed a significant but conflicting role of apolipoprotein E (APOE) isoforms in warfarin pharmacogenetics. The contribution of APOE isoforms in influencing variations in warfarin requirements in Asian subjects remains to be investigated.
  
  
  CONCLUSIONS
  This is the first report of a population study in Asians exploring the role of isoforms encoded by three APOE alleles (epsilon 2, epsilon 3, epsilon 4) in influencing warfarin dose requirements. The present study showed that the APOE epsilon 3/epsilon 3 isoform is the predominant genotype in the Asian population. The study also showed that APOE isoforms may not be important in affecting warfarin pharmacodynamics in Asian patients. It also suggested that the impact of different APOE isoforms depended on the frequency of APOE genotypes in the population, in particular the epsilon 4 allele containing genotypes.
  
  
  OBJECTIVE
  To investigate the influence of APOE genotypes and VKORC1 haplotypes on warfarin dose requirements in Asian patients.
  
  
  METHODS
  A total of 174 Asian patients (Chinese, n = 96; Malays, n = 50; Indians, n = 28) who had stable daily warfarin doses for at least 1 month were recruited. Following genomic DNA extraction from venous blood, pharmacogenetic analysis of APOE and VKORC1 genes was done by DNA sequencing.
  
  
  RESULTS
  The majority of the Asian patients (78%) harboured the APOE epsilon 3/epsilon 3 genotype. Different APOE genotypes were found not to have any significant influence on mean daily warfarin dose requirements. Warfarin dose requirements in the pooled Asian patients homozygous for the VKORC1 H1 haplotype were significantly lower compared with patients homozygous for the H7 haplotype (H1-H1 vs. H7-H7: 2.79 +/- 1.06 mg day(-1)vs. 5.45 +/- 2.3 mg day(-1), P < 0.001).
  
  
  CONCLUSIONS
  The present study suggests that APOE variants have minimal impact on warfarin dose requirements in Asian patients, probably due to the low frequency of epsilon 4 allele containing genotypes.
authors.affiliation: Laboratory of Clinical Pharmacology, Division of Medical Sciences, Humphrey Oei Institute of Cancer Research, National Cancer Centre, Singapore.
authors.forename: Suman
authors.initials: S
authors.lastname: Lal
authors.forename: Edwin
authors.initials: E
authors.lastname: Sandanaraj
authors.forename: Srinivasa Rao
authors.initials: SR
authors.lastname: Jada
authors.forename: Ming-Chai
authors.initials: MC
authors.lastname: Kong
authors.forename: Lai-Heng
authors.initials: LH
authors.lastname: Lee
authors.forename: Boon-Cher
authors.initials: BC
authors.lastname: Goh
authors.forename: Soo-Chin
authors.initials: SC
authors.lastname: Lee
authors.forename: Balram
authors.initials: B
authors.lastname: Chowbay
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001057:Apolipoproteins E / Q000235:genetics*; D044466:Asian People / Q000235:genetics*; D014644:Genetic Variation / Q000187:drug effects / Q000235:genetics; D005838:Genotype; D006239:Haplotypes / Q000235:genetics*; D006720:Homozygote; D006801:Humans; D008875:Middle Aged; D006899:Mixed Function Oxygenases / Q000235:genetics*; D020033:Protein Isoforms / Q000235:genetics; D064417:Vitamin K Epoxide Reductases; D014859:Warfarin / Q000008:administration & dosage*
chemical_list: D001057:Apolipoproteins E; D020033:Protein Isoforms; D014859:Warfarin; D006899:Mixed Function Oxygenases; C578523:VKORC1 protein, human; D064417:Vitamin K Epoxide Reductases