Association of racially dimorphic PAR4 variants with platelet PAR4 function. (A) Manhattan plot showing association of SNPs in the F2RL3 gene with platelet PAR4-AP reactivity. Each circle represents a SNP. The circles for rs773903 and rs773904 overlap. Y-axis is –log10 of the P values for association, controlling for age, race, and sex; x-axis, chromosomal location. (B) Schematic of F2RL3 and LD plot of SNPs in F2RL3. Nonsynonymous SNPs coding changes are shown above the schematic. Red rs numbers indicate SNPs identified in quantitative trait locus analysis; blue rs number indicates a less common SNP observed only in black subjects. (C) Genotype and allele frequency of rs773902 in black and white PRAX1 subjects. (D) Worldwide allele frequency of rs773902 in HGDP data set.