A genome-wide association study of heparin-induced thrombocytopenia using an electronic medical record

Abstract

Heparin-induced thrombocytopenia (HIT) is an unpredictable, potentially catastrophic adverse effect of heparin treatment resulting from an immune response to platelet factor 4 (PF4)/heparin complexes. No genome-wide evaluations have been performed to identify potential genetic influences on HIT. Here, we performed a genome-wide association study (GWAS) and candidate gene study using HIT cases and controls identified using electronic medical records (EMRs) coupled to a DNA biobank and attempted to replicate GWAS associations in an independent cohort. We subsequently investigated influences of GWAS-associated single nucleotide polymorphisms (SNPs) on PF4/heparin antibodies in non-heparin treated individuals. In a recessive model, we observed significant SNP associations (odds ratio [OR] 18.52; 95% confidence interval [CI] 6.33-54.23; p=3.18×10(-9)) with HIT near the T-Cell Death-Associated Gene 8 (TDAG8). These SNPs are in linkage disequilibrium with a missense TDAG8 SNP. TDAG8 SNPs trended toward an association with HIT in replication analysis (OR 5.71; 0.47-69.22; p=0.17), and the missense SNP was associated with PF4/heparin antibody levels and positive PF4/heparin antibodies in non-heparin treated patients (OR 3.09; 1.14-8.13; p=0.02). In the candidate gene study, SNPs at HLA-DRA were nominally associated with HIT (OR 0.25; 0.15-0.44; p=2.06×10(-6)). Further study of TDAG8 and HLA-DRA SNPs is warranted to assess their influence on the risk of developing HIT.

Keywords: Pharamacogenetics; heparins; thrombocytopenia.

Figure 1

Manhattan plot of genotyped SNPs associated with heparin-induced thrombocytopenia in a recessive model, adjusted for age, gender, UFH versus LMWH, and principal components 1 and 2. P values on the −log₁₀ scale are plotted on the vertical axis and the chromosomal position is plotted along the horizontal axis. Dots representing SNPs on different chromosomes have alternating orange and blue color. The red line indicates the genome-wide significance threshold of alpha=5×10⁻⁸.

Figure 2

Locuszoom plot of most strongly associated SNPs in TDAG8 (GPR65) and the surrounding region using imputed SNPs. P values were generated using logistic regression adjusted for age, gender, UFH versus LMWH, and principal components 1 and 2 in a recessive model. P values on the −log₁₀ scale are plotted on the left vertical axis and the chromosomal position is plotted along the horizontal axis along with the gene names and size of flanking region. The most strongly associated SNP rs10782473 is indicated by a purple diamond and pairwise LD (r²) with this SNP is indicated by dot color as described in the legend in the upper right corner. The right vertical axis indicates the regional recombination rate (cM/Mb) which is overlaid in light blue.

Figure 3

Locuszoom plot of most strongly associated SNPs from the candidate gene study in HLA-DRA and the surrounding region plus or minus 10,000 base pairs. P values were generated using logistic regression adjusted for age, gender, UFH versus LMWH, and principal components 1 and 2 in a recessive model. P values on the −log₁₀ scale are plotted on the left vertical axis and the chromosomal position is plotted along the horizontal axis along with the gene names and size of flanking region. Pairwise LD (r²) is indicated by dot color as described in the legend in the upper left corner. The right vertical axis indicates the regional recombination rate (cM/Mb) which is overlaid in light blue.