PAR4 variants and platelet function. Platelet PAR4 reactivity by rs773902 genotype for (A) all participants and (B) each race individually. P = 9.15 × 10⁻¹⁶, association of PAR4 reactivity with rs773902 genotype by linear regression. (C) Platelet ARS of PRAX1 subjects for AA, adenosine 5′-diphosphate, collagen-related peptide, α-CD9 antibody (CD9), PAR1-AP (PAR1), and PAR4-AP (PAR4), segregated by rs773902 genotype. One-way ANOVA showed no association between rs773902 and any agonist except PAR4-AP (PAR4-AP [A] is shown again for ease of comparison). (D) Platelet calcium flux from subjects genotyped for rs773902 (cohort 2). Platelets were treated with 50 μM PAR4-AP. n = 10 GG; n = 5 AA/AG. P = .03 1-tailed t test. (E) Platelet PAR4 reactivity by rs773902 and rs2227346 genotypes among self-identified black subjects in PRAX1. P = 1.75x10⁻⁸, association of PAR4 reactivity with rs2227346 genotype partial F-test after controlling for rs773902 genotype. For all panels, the box represents the interquartile range, the horizontal line in box is the median, and the whiskers represent 1.5 times interquartile range.