De T, et al. – In this preliminary, case-control, genome-wide association study involving patients of African descent taking warfarin at an international normalized ratio (INR) of < 4, researchers identified genetic factors related to warfarin-related bleeding. Findings showed that four single-nucleotide polymorphisms (SNPs) in linkage disequilibrium on chromosome 6 were related to an increased risk of major bleeding at INR of < 4.

Methods

• This investigation involving patients of African descent taking warfarin was conducted in a discovery cohort (University of Chicago [2009-2011] and the University of Illinois at Chicago [2002-2011]), and associations were confirmed in a replication cohort (University of Chicago [2015-2016]).
• By principal component analysis, potential population stratification was examined in the discovery cohort.
• By logistic regression analysis, odds ratios (ORs) and 95% CIs were computed for bleeding risk.
• With a fixed effects meta-analysis, summary statistics from the discovery and the replication cohorts were analyzed.
• Using luciferase expression assays, the investigators examined the potential influence of SNPs on gene expression.
• The exposures analyzed included SNPs associated with warfarin-related bleeding.
• The main outcomes and measures analyzed included major bleeding—characterized as bleeding requiring hospitalization, causing a decrease in hemoglobin level > 2 g/dL, requiring blood transfusion, or any combination of the three—while taking warfarin at an INR of < 4.

Results

• The discovery cohort consisted of 31 cases (mean age, 60.1 years [SD, 14.9 years]; 26 women [83.9%]) and 184 warfarin-treated control participants (mean age, 57.1 years [SD, 15.7 years]) with no documented bleeding.
• The replication cohort consisted of 40 cases (mean age, 55.6 years [SD, 17.3 years]; 27 women [67.5%]) and 148 warfarin-treated control participants (mean age, 55.4 years [SD, 17.1 years]; 98 women [66.2%]) with no documented bleeding.
• Four SNPs in linkage disequilibrium on chromosome 6 (rs115112393, rs16871327, rs78132896, and rs114504854) were found to be related to warfarin-related bleeding but did not reach genome-wide significance in the discovery cohort.
• Findings revealed that the SNP rs78132896 occurred in 11 cases (35.5%) and 9 control participants (4.9%) in the discovery cohort (OR, 8.31; 95% CI, 3.2-21.5; P < 6.21 × 10⁻⁸), and the association was confirmed in the replication cohort (the SNP was present in 14 cases [35.0%] and 7 control participants [4.8%]; OR, 8.24; 95% CI, 3.1-25.3, P=5.64 × 10⁻⁵).
• When the cohorts were combined by meta-analysis (OR, 8.27; 95% CI, 4.18-16.38; P=2.05 × 10⁻¹¹), genome-wide significance of this SNP was achieved.
• These SNPs were only found in those of African descent.
• In vitro luciferase expression assays showed that rs16871327 (enhancer SNP) and rs78132896 (promoter SNP) risk alleles together increased EPHA7 gene (Entrez Gene 2045) transcription by a mean of 14.95 (SD, 1.7) vs wild-type alleles (mean, 9.56 [SD, 0.84]; difference, 5.39; 95% CI, 4.1-6.6; P < 0.001).