Abstract P261: Methylation Status of VKORC1 and Warfarin Dose
Introduction: It is well known that genetic variants, especially in the VKORC1 and CYP2C9 genes, can be associated with warfarin maintenance dose. However, currently known genetic variants fail to explain a large portion of the observed variability in warfarin dose, especially in African American patients. Methylation is a heritable epigenetic modification in which conversion of cytosine residues within “CpG islands” to 5-methylcytosine is associated with reduced gene expression. To our knowledge, the effect of methylation status on warfarin dose has never been studied.
Hypothesis: We hypothesized that higher rates of methylation near the start region of VKORC1 in whole blood would be associated with lower required maintenance dose in warfarin patients.
Methods: We conducted a prospective cohort study of patients initiating warfarin at three anticoagulation clinics. All individuals with available methylation data who reached maintenance dose were included in the analysis (N = 237). Methylation status was assessed in the region from 1500bp upstream to 500bp downstream of the VKORC1 start site using the Sequenom EpiTYPER assay on DNA extracted from whole blood. Linear regression was used to assess the association between methylation levels at individual CpG sites (66 total) and required warfarin maintenance dose. Visual inspection of univariable results was used to identify potentially important CpG clusters, which were subsequently examined using univariable and multivariable linear regression, with the latter adjusting for the effects of race, presence of VKORC1 variant, and other well-known predictors of warfarin dose.
Results: Two of 66 CpG sites were nominally associated with lower maintenance dose requirement on univariable analysis. These CpG sites were identified as part of a CpG cluster located approximately 330 to 226bp upstream of the VKORC1 start site. Median methylation levels in this cluster was 16% (IQR 15%, 17%). A 1% increase in methylation in this cluster was associated with a 2.8 mg/wk reduction in weekly warfarin maintenance dose (P = 0.02). No significant interaction between methylation status and African American race was observed (P = 0.77). This association was substantially attenuated with the inclusion of VKORC1 variant status in the model (P = 0.33).
Conclusions: Preliminary evidence suggests that methylation levels in a CpG cluster in VKORC1 may be moderately associated with warfarin maintenance dose, although this association may not be independent of VKORC1 variant status. However, these results require confirmation from additional epidemiological studies and possibly functional assays in liver tissue.
Author Disclosures: B.S. Finkelman: None. L. Bershaw: None. J. Chen: None. C.M. Brensinger: None. R.C. Li: None. S.E. Kimmel: G. Consultant/Advisory Board; Modest; Served on DSMBs for Johnson and Johnson, unrelated to warfarin. G. Consultant/Advisory Board; Significant; Consulted for Pfizer, unrelated to warfarin.
- © 2014 by American Heart Association, Inc.