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Background: Plasma proteins are critical mediators of cardiovascular processes and are the targets of many drugs. Previous efforts to characterize the genetic architecture of the plasma proteome have been limited by a focus on individuals of European descent and leveraged genotyping arrays and imputation. Here we describe whole genome sequence analysis of the plasma proteome in individuals with greater African ancestry, increasing our power to identify novel genetic determinants. Methods: Proteomic profiling of 1301 proteins was performed in 1852 Black adults from the Jackson Heart Study using aptamer-based proteomics (SomaScan). Whole genome sequencing association analysis was ascertained for all variants with minor allele count ≥5. Results were validated using an alternative, antibody-based, proteomic platform (Olink) as well as replicated in the Multi-Ethnic Study of Atherosclerosis and the HERITAGE Family Study (Health, Risk Factors, Exercise Training and Genetics). Results: We identify 569 genetic associations between 479 proteins and 438 unique genetic regions at a Bonferroni-adjusted significance level of 3.8×10 -11 . These associations include 114 novel locus-protein relationships and an additional 217 novel sentinel variant-protein relationships. Novel cardiovascular findings include new protein associations at the APOE gene locus including ZAP70 (sentinel single nucleotide polymorphism [SNP] rs7412-T, β=0.61±0.05, P =3.27×10 -30 ) and MMP-3 (β=-0.60±0.05, P =1.67×10 -32 ), as well as a completely novel pleiotropic locus at the HPX gene, associated with 9 proteins. Further, the associations suggest new mechanisms of genetically mediated cardiovascular disease linked to African ancestry; we identify a novel association between variants linked to APOL1-associated chronic kidney and heart disease and the protein CKAP2 (rs73885319-G, β=0.34±0.04, P =1.34×10 -17 ) as well as an association between ATTR amyloidosis and RBP4 levels in community-dwelling individuals without heart failure. Conclusions: Taken together, these results provide evidence for the functional importance of variants in non-European populations, and suggest new biological mechanisms for ancestry-specific determinants of lipids, coagulation, and myocardial function.

Platelets are critical in inflammation, wound healing, and thrombosis. Platelet count (PLT) and mean platelet volume (MPV) are heritable, frequently assessed measures for which hundreds of genetic associations have been identified, predominantly in European populations. However, causal variants are unknown at most loci, and additional genetic determinants in diverse ancestral populations remain to be discovered. We performed a multi-ancestry whole genome sequencing analysis for PLT in three Phase 1 TOPMed cohorts, the European American Framingham Heart (FHS, n=2259) and Old Order Amish (OOA, n=1095) studies and the African American Jackson Heart Study (JHS, n=3523). MPV was additionally analyzed in JHS and FHS. Heritability in JHS and FHS was 45-73%. Single variant and aggregate burden and sequence kernel association (SKAT) tests [5 and 50 kilobase (kb) sliding windows] were performed using a mixed model approach in GENESIS, with aggregate tests for variants with a minor allele frequency (MAF) < 1% only. Inverse normalized residuals were adjusted for sex, age, study, and an empirical genetic relationship matrix, allowing for heterogeneous variance by study. For PLT, several associations had the same index SNP ( ARHGEF3 , TPM4 ) or were in moderate LD ( TAOK1 , r 2 =0.46) with a previously reported signal; two associations were not in LD (r 2 -8 , MAF=16%), an intergenic variant upstream of telomerase reverse transcriptase ( TERT ), is common only in African ancestry populations (~36%, 1% in Europeans) and was significant only in JHS (p=4.7 x 10 -9 , p=0.91 FHS, absent OOA). This variant and an LD proxy (rs10052815) overlap a GATA1 binding site in erythroblasts, the sister lineage of platelet producing megakaryocytes. An intronic TERT variant (rs2736100) 17 kb away (r 2 =0.025, D’=0.418 in included TOPMed cohorts) has been associated with PLT in Europeans, as well as with red blood cell traits, telomere length, pulmonary fibrosis, and multiple cancer subtypes. The second locus (rs73437176, p=1.5 x 10 -8 , MAF=12%), an intronic variant in progestin and adipoQ receptor family member V ( PAQR5 ), is also more frequent in African ancestry populations (~25%, 4% in Europeans) and significant only in JHS (p=2.5 x 10 -8 , FHS p=0.47, OOA p=0.12); the nearest previously identified signal is ~4 Mb away and not in significant LD (D’DNM3 , ARHGEF3 , CCDC71L , JMJD1C , RHOF , TAOK1 , TPM4 ), with either the same lead variant as previously reported or a variant in close LD (r 2 >0.75). Aggregated sliding window tests did not identify any additional signals. These results show suggestive evidence for association with PLT for two novel variants common only in African ancestry populations, but larger sample sizes of diverse ancestry will be necessary for replication and further discovery of novel loci.

Background: The biology of platelets_anuclear megakaryocyte fragments required for clotting_is well defined, with abnormalities resulting in clotting disorders ranging from asymptomatic to severe. Although platelet count (PLT) is highly heritable (h 2 =0.57 in NHANES), genetic regulation of this trait remains incompletely characterized. In particular, Hispanic Latinos are a diverse population in which the genetic variability of PLT has not been analyzed. We aimed to 1) identify novel loci associated with PLT in participants of HCHS/SoL; and 2) determine if previously identified PLT loci generalize to the Hispanic Latino population. Methods: We performed a genome-wide association study of PLT in 12,491 participants of HCHS/SoL, which includes individuals with Dominican, Puerto Rican, Mexican, Cuban, South American, and Central American ancestral origins residing in the United States. Participants were genotyped on the Illumina SoL Omni2.5M array and imputed to the 1000 Genomes Phase I Reference panel. We implemented linear mixed-model regression assuming an additive genetic model, adjusting for sex, age, study center, ancestry and sample weights, and including random effects for individual relatedness, household, and block group. Results: Ten independent loci were significantly (α = 5x10 -8 ) associated with PLT in HCHS/SoL and 13 of 57 previously identified platelet-count GWAS loci generalized to HCHS/SoL (+/-500kb, α = 8.78x10 -4 ). Discovery loci included a significant association near GABBR1 (rs3131857, MAF = 40%, β = -0.16) and a suggestive association near ETV7 (rs9470264, MAF = 20%, β = -0.19). Furthermore, a noncoding variant in ACTN1 was associated with increased PLT (rs117672662, MAF = 6%, β = 0.61); ACTN1 codes for alpha-actinin, a multi-isoform actin-binding protein involved in cytoskeleton organization and platelet/megakaryocyte structural integrity. Missense mutations in ACTN1 were recently implicated in congenital thrombocytopenia; exome sequencing also associated this locus with PLT, which supports a potential functional role in PLT for this gene. Conditional regression analyses to assess secondary association signals are in progress. Conclusions: Genetic associations in two discovery loci ( ETV7 and GABBR1 ) underscore the benefit of using diverse populations in GWAS. Expanding the number of loci associated with platelet count will help elucidate disease mechanisms and develop approaches to treat platelet disorders in populations of all ancestries.