Abstract MP60: Investigation of Blood Pressure Genetic Loci in African Americans using the Metabochip
Authors: Carty Cara L , Hindorff Lucia A , Buyske Steven , Haessler Jeff , Fesinmeyer Megan D , Carlson Chris S , Rao DC , Chakravarti Aravinda , Fornage Myriam , North Kari E , Kooperberg Charles , Franceschini Nora ,   on behalf of the Population Architecture using Genomics and Epidemiology (PAGE) Study Investigators
Published: July 2021

Introduction.
African Americans (AA) have a higher burden of hypertension than European descent individuals, thus motivating research on blood pressure (BP) risk factors in AA, including genetic variants. Yet to date, few genome-wide association studies (GWAS) of BP have been conducted in AA and it is unclear whether genetic variants identified in mainly European descent populations are also associated with BP in AA. Furthermore, investigation of established BP loci in diverse race/ethnicity groups such as AA, who tend to have higher levels of genetic diversity, provides opportunities to narrow loci for identifying potential causal variants.

Methods.
We examined whether systolic BP (SBP) and diastolic BP (DBP) loci on the Illumina Metabochip array were associated with BP traits in 18,832 AA from the PAGE, HyperGen and GenNet studies. Only SNPs with minor allele frequency≥0.001 and passing stringent QC were tested. Using p-value<0.05 as a significance threshold for replication of GWAS SNPs in our AA population, we investigated the original GWAS SNP and all SNPs ±500 kilobases in modest linkage disequilibrium with it (r
2
≥0.3). To test SNPs in the 16 SBP and 14 DBP loci, we used a Bonferroni corrected p-value of 0.05/total SNPs per locus (the number SNPs at each BP locus ranges from 104 to 2,337).

Results.
In models adjusted for sex, age, body mass index and global ancestry, 5 prior GWAS SNPs were associated (p<0.05) with DBP: rs13107325/
SLC39A8
(non-synonymous), rs1165196/
SLC17A1
(non-synonymous), rs6495122/
CPLX3
, rs1327235/intergenic and rs6015450/intergenic. At several loci, we identified finely-mapped SNPs more strongly associated with DBP in AA than the original GWAS SNPs. Notably, we identified rs56153133 in the gene-rich 1p26 region harboring the chloride channel-voltage-sensitive-6 (
CLCN6
) gene, p=6.9E-5. This SNP is highly correlated with the GWAS SNP rs17367504/
MTHFR
in European-descent individuals (r
2
=0.98) and less so in AA (r
2
=0.64). For SBP, we replicated two GWAS SNPs: rs16998073/intergenic and rs2681472/
ATP2B1
and at many loci (10q24, 1p26, 15q26
et al
.), we identified SNPs more strongly associated with SBP in AA than the original GWAS SNPs.

Conclusions.
Overall, several BP loci originally reported in individuals of European and East Asian ancestry also generalize to AA, which confirms the relevance of specific BP susceptibility loci across diverse populations. In addition, we identified SNPs more strongly associated with BP traits in AA than the original GWAS SNPs, underlying the importance of leveraging differences in nucleotide diversity and LD patterns among populations to narrow GWAS signal boundaries. Future work will include conditional analysis to further refine GWAS loci, and to identify additional signals and population-specific variation.