Abstract 25: Epigenome-Wide DNA Methylation Analysis Reveals Novel Hematologic Trait Associations for African Americans in The Jackson Heart Study
Authors: Szeto Mindy D , Raffield Laura M , Nickerson Deborah A , Zakai Neil A , Klemm Dwight J , Taylor Matthew R , Yang Ivana V , Correa Adolfo , Reiner Alex P , Lange Ethan M , Lange Leslie A 
Published: March 2020

Cardiovascular disease (CVD) is the leading cause of death in the U.S. and disproportionately affects African Americans (AAs). Routinely measured circulating red blood cell traits, which are highly heritable and differ by ethnicity, are independent predictors for CVD-related traits including hypertension, stroke, coronary heart disease, and CVD mortality. Many genetic loci associated with red blood cell count (RBC), hemoglobin (HGB), hematocrit (HCT), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), and red cell distribution width (RDW) have been identified. However, identified genetic variants do not fully explain the heritability of these traits. Epigenetic alterations in DNA methylation likely also explain a portion of red cell trait variance, and detecting methylation quantitative trait loci (meQTLs) can provide critical insight into the development of CVD and CVD health disparities. We performed an epigenome-wide association analysis to identify CpG sites at which DNA methylation levels are associated with red blood cell traits in 1753 participants from the Jackson Heart Study, a population-based cohort of AAs. DNA methylation was measured by the Illumina MethylationEPIC array, interrogating approximately 850,000 CpG sites in peripheral blood mononuclear cells at the baseline exam. Associations were assessed using linear mixed models adjusted for age, sex, cell proportions, genetic ancestry, and experimental batch effects. A Bonferroni-corrected p-value of 9x10
-8
was used to assess statistical significance. We identified many significant differentially methylated CpG sites associated with red blood cell traits. Analysis of RBC, HGB, MCV, MCH, and MCHC revealed a novel highly significant association with a CpG annotated to a non-coding RNA (cg11703701; RBC P = 5.19x10
-22
, HGB P = 1.19x10
-11
, MCV P = 4.69x10
-59
, MCH P = 2.68x10
-67
, MCHC P = 2.32x10
-31
), as well as a strong signal for a reprogramming-specific differentially methylated region (cg04321267; RBC P = 1.67x10
-16
, HGB P = 3.58x10
-12
, MCV P = 2.12x10
-49
, MCH P = 1.74x10
-57
, MCHC P = 5.91x10
-30
). Multiple CpGs annotated to genes
HBA1
and
HBA2
were associated with RBC, MCV, MCH, and MCHC, while
ITPKB
(cg23740281; HGB P = 4.88x10
-10
, HCT P = 6.20x10
-11
) and
ALDH2
(cg17969951; HGB P = 3.03x10
-11
, HCT P = 8.31x10
-9
) were significantly associated with both HGB and HCT. Additional CpG sites were significantly associated with HCT (
PLXND1
cg22902177; P = 7.54x10
-11
and
ARL1
cg23903357; P = 9.86x10
-11
) and RDW (
CPNE2
cg09018739; P = 3.03x10
-22
). These findings shed light on potential hematologic and CVD mechanisms in understudied populations. Future work will explore the role of neighboring SNPs in mediating observed methylation-trait associations, and replicate results in an additional multi-ethnic cohort.