Warfarin pharmacogenetics : a single VKORC1 polymorphism is predictive of dose across three racial groups

• Warfarin dosing algorithms incorporating CYP2C9 and VKORC1-1639G>A improve dose prediction compared to algorithms based solely on clinical and demographic factors. However these algorithms better capture dose variability among Whites compared to Asians or Blacks. Herein we evaluate whether other VKORC1 polymorphisms and haplotypes explain additional variation in warfarin dose beyond that explained by VKORC1-1639G>A among Asians (n=1103), Blacks (n=670) and Whites (n=3113). Participants were recruited from 11 countries as part of the International Warfarin Pharmacogenetics Consortium effort. Evaluation of the effects of individual VKORC1 SNPs and haplotypes on warfarin dose employed both univariate and multivariable linear regression. VKORC1-1639G>A and 1173C>T individually explained the greatest variance in dose in all three racial groups. Incorporation of additional VKORC1 SNPs or haplotypes did not further improve dose prediction. VKORC1 explained greater variability in dose among Whites as compared to Blacks and Asians. Differences in the percent variance in dose explained by VKORC1 across race was largely accounted for by the frequency of the -1639 A (or 1173 T) allele. Thus, clinicians should recognize that although at a population level, the contribution of VKORC1 towards dose requirements is higher in Whites compared to non-whites; genotype predicts similar dose requirements across racial groups.

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