A polymorphism in the VKORC1 regulator calumenin predicts higher warfarin dose requirements in African Americans

Abstract

Warfarin demonstrates a wide interindividual variability in response that is mediated partly by variants in cytochrome P450 2C9 (CYP2C9) and vitamin K 2,3-epoxide reductase complex subunit 1 (VKORC1). It is not known whether variants in calumenin (CALU) (vitamin K reductase regulator) have an influence on warfarin dose requirements. We resequenced CALU regions in a discovery cohort of dose outliers: patients with high (>90th percentile, n = 55) or low (<10th percentile, n = 53) warfarin dose requirements (after accounting for known genetic and nongenetic variables). One CALU variant, rs339097, was associated with high doses (P = 0.01). We validated this variant as a predictor of higher warfarin doses in two replication cohorts: (i) 496 patients of mixed ethnicity and (ii) 194 African-American patients. The G allele of rs339097 (the allele frequency was 0.14 in African Americans and 0.002 in Caucasians) was associated with the requirement for a 14.5% (SD +/- 7%) higher therapeutic dose (P = 0.03) in the first replication cohort and a higher-than-predicted dose in the second replication cohort (allele frequency 0.14, one-sided P = 0.03). CALU rs339097 A>G is associated with higher warfarin dose requirements, independent of known genetic and nongenetic predictors of warfarin dose in African Americans.

Figure 1

Schematic of two-stage study design using a parent cohort of patients on stable warfarin therapy. In the discovery cohort (left panel, we sequenced CALU in patients who had the largest or smallest residual dosing errors (shaded) within the parent cohort. In the second stage, significant (P < 0.05, FDR < 0.010) SNPs from the discovery stage were then genotyped in the remainder of the parent cohort (shaded, replication cohort 1, right panel). Predicted doses were based on a validated pharmacogenetics algorithm.⁹ CALU, calumenin; FDR, false-discovery rate; SNP; single-nucleotide polymorphism.

Figure 2

Carriers of CALU SNP rs339097 require higher-than-predicted therapeutic warfarin doses in the combined discovery and replication cohort 1. Therapeutic dose vs. predicated dose (based on a validated pharmacogenetic algorithm⁹) in carriers (•) and noncarriers (+) of the G allele for CALU rs339097. In this combined cohort, 25 of 31 (83%) carriers of the G allele required a higher-than-predicated warfarin dose to achieve a therapeutic INR. CALU, calumenin; INR, international normalized ratio; SNP, single-nucleotide polymorphism; WT, wild type.