title: New genetic variant that might improve warfarin dose prediction in African Americans.
abstract: BACKGROUND
  Variants in the CYP2C9 (i.e. *2 and *3) and VKORC1 (i.e. 1173C/T or -1639G/A) genes have been shown to influence warfarin dose requirements. However, these factors seem to explain less of the dose variability in African Americans who have a lower prevalence of the CYP2C9*2 and *3 and VKORC1 1173T alleles.
  
  
  CONCLUSIONS
  In African Americans, the VKORC1 rs17886199 variant was statistically significantly associated with log-transformed warfarin maintenance dose, independent of the influence of VKORC1 1173C>T and CYP2C9*2 and *3. However, replication of our finding is needed to confirm the association of rs1786199 SNP in African Americans, since Limdi et al.[3] did not examine the effect of this SNP because the prevalence of the rs1786199 A-allele was too low.
  
  
  OBJECTIVE
  To raise hypotheses with regards to whether genetic variants in the VKORC1, CYP2C9, EPHX1, GGCX and ALB genes might influence warfarin dose in African Americans and Caucasians, independent of the effects of the VKORC1 1173C>T and CYP2C9*2 and *3 variants.
  
  
  METHODS
  From a prospective cohort study, we obtained additional DNA on 36 Caucasian and 22 African American warfarin users who reached maintenance dose and genotyped them for tagSNPs (r2<0.8) in VKORC1, EPHX1, GGCX and ALB genes, and one exonic CYP2C9 SNP. Linear regression models were fitted to estimate the relationship (P value) between log-transformed maintenance dose and each SNP and the amount of the warfarin dose variability accounted for by each SNP (partial R2).
  
  
  RESULTS
  In African Americans, the VKORC1 rs17886199 A-allele was associated with a lower dose (GG=46.3 mg and GA=25.6 mg; P=0.002), independent of the VKORC1 1173C>T and CYP2C9*2 and *3 variants. Even after applying Bonferroni correction, the P value would still be considered statistically significant. The VKORC1 rs17886199 variant was not found in Caucasians. In Caucasians, the EPHX1 rs1051741 T-allele was associated with a lower dose (CC=41.3 mg and CT=30.0 mg; P=0.04). The latter was no longer statistically significant after applying Bonferroni correction.
  
  
  CONCLUSIONS
  Our pilot study suggests that the VKORC1 rs17886199 variant could influence warfarin maintenance dose among African Americans, even after accounting for the influence of the VKORC1 1173C>T variant. Future studies with a larger sample size will be needed to confirm our findings.
authors: Center for Clinical Epidemiology and Biostatistics, Department of Epidemiology and Biostatistics, University of Pennsylvania School of Medicine, Pittsburgh, PA 19104-6021, USA.
authors: Hedi
authors: H
authors: Schelleman
authors: Colleen M
authors: CM
authors: Brensinger
authors: Jinbo
authors: J
authors: Chen
authors: Brian S
authors: BS
authors: Finkelman
authors: Mark J
authors: MJ
authors: Rieder
authors: Stephen E
authors: SE
authors: Kimmel
mesh_terms: D000328:Adult; D001741:Black or African American / Q000235:genetics*; D000368:Aged; D000369:Aged, 80 and over; D000483:Alleles; D000925:Anticoagulants / Q000494:pharmacology*; D001189:Aryl Hydrocarbon Hydroxylases / Q000235:genetics; D015331:Cohort Studies; D065729:Cytochrome P-450 CYP2C9; D004305:Dose-Response Relationship, Drug; D005838:Genotype; D006801:Humans; D008875:Middle Aged; D006899:Mixed Function Oxygenases / Q000235:genetics*; D011110:Polymorphism, Genetic / Q000187:drug effects*; D011446:Prospective Studies; D012044:Regression Analysis; D064417:Vitamin K Epoxide Reductases; D014859:Warfarin / Q000494:pharmacology*; D044465:White People / Q000235:genetics*; D055815:Young Adult
chemical_list: D000925:Anticoagulants; D014859:Warfarin; D006899:Mixed Function Oxygenases; C450260:CYP2C9 protein, human; D065729:Cytochrome P-450 CYP2C9; D001189:Aryl Hydrocarbon Hydroxylases; C578523:VKORC1 protein, human; D064417:Vitamin K Epoxide Reductases