Left ventricular (LV) remodeling and hypertrophy occurs frequently in the general population and is a strong predictor of myocardial infarction, heart failure, and stroke. Data previously collected in the HyperGEN and GENOA studies of the Family Blood Pressure Program (FBPP) have pointed to genetic loci contributing to LV hypertrophy and dimensional traits through linkage studies and genome-wide association studies. Despite these advances, a large portion of variation in LV traits is unaccounted for. We hypothesize that, in part, rare variants account for this variation. We propose the following aims.
Aim 1. Whole exome sequence (WES) 1,200 AA unrelated hypertensives with extreme values for echocardiographic LV mass/hgt2.7 to identify rare and low-frequency variants contributing to LV mass and related structural and functional phenotypes. We will select unrelated individuals from the top and bottom quartile of LV mass index. Because the distribution of LV mass/hgt2.7 in the FBPP is shifted to higher values than the general population, the cutpoint for the upper quartile is approximately equal to the definition of LVH. We will sequence at a density sufficient to capture rare variants. We will conduct extreme phenotype-based analysis, weighted by function and conservation, to identify high-impact coding variants. A gene list will be ranked for selection in Aim 2 based on evidence from statistical and bioinformatic analyses and expression experiments in induced pluripotent stem cell- (iPSC-)derived cardiomyocytes.
Aim 2. Validate variants detected in Aim 1 by resequencing 40 candidate genes in all AA HyperGEN/GENOA family members, and subsequently validate 768 most significant variants in external cohorts. We will sequence all exons and regulatory regions in the remainder of the FBPP families and siblings not sequenced in Aim 1 (n=2,266). We will conduct association analysis followed by bioinformatic filtering to identify high-impact coding variants and rank the 768 most significant variants for further external replication. We will genotype these in 9,160 AA (5,623 hypertensive) participants from population-based studies using Illumina assays (ie, JHS, CARDIA, ARIC, CHS, WUSTL). Gene-based associations will be examined within and meta-analyzed among cohorts. Genes will be ranked by statistical and biological evidence to move to Aim 3.
Aim 3. Use human iPSC cardiomyocytes to functionally validate variants replicated in Aim 2. Using hypertrophy-induced cardiomyocytes, we will test the direction of effect and clinical characterization of associated genes with rare variants from Aim 2. We will use siRNA transfections to test whether knock down of candidate genes influences hypertrophy in the cell-based model. The research proposed herein, if successful, will continue the success of HyperGEN and GENOA in identifying novel genes contributing to LV hypertrophy, and evaluate their relevance in a cell-based system to identify new pathways for future treatment.
Black people tend to have an enlarged left ventricle (the heart chamber that pumps oxygenated blood throughout the body) more commonly than those in other race groups, putting them at greater risk for having potentially fatal cardiovascular diseases. Enlarged left ventricles are caused, at least in part, by a person's genes. This study seeks to discover which genetic factors may cause an enlarged heart; this may ultimately lead to new diagnoses and treatments to help lower cardiovascular disease risk in blacks.
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