Distribution of anti-PF4/heparin antibody titers. Antibody titer distribution by the genotype of the 2 most highly associated SNPs that passed the suggestive significance threshold in the discovery cohort and were associated in the replication cohort. Violin plots show the proportion of individuals across antibody titer values (optical density [OD]) within each genotype. The top panels show rs1555175145 in the discovery cohort (A) and replication cohort (B). The bottom panels show rs149530346 in the discovery cohort (C) and replication cohort (D). β, standard errors, and P values using linear regression adjusted for age, sex, and principal components 1 to 3 are listed at the bottom of each figure.