Genomewide association study using a high-density single nucleotide polymorphism array and case-control design identifies a novel essential hypertension susceptibility locus in the promoter region of endothelial NO synthase

Abstract

Essential hypertension is a multifactorial disorder and is the main risk factor for renal and cardiovascular complications. The research on the genetics of hypertension has been frustrated by the small predictive value of the discovered genetic variants. The HYPERGENES Project investigated associations between genetic variants and essential hypertension pursuing a 2-stage study by recruiting cases and controls from extensively characterized cohorts recruited over many years in different European regions. The discovery phase consisted of 1865 cases and 1750 controls genotyped with 1M Illumina array. Best hits were followed up in a validation panel of 1385 cases and 1246 controls that were genotyped with a custom array of 14 055 markers. We identified a new hypertension susceptibility locus (rs3918226) in the promoter region of the endothelial NO synthase gene (odds ratio: 1.54 [95% CI: 1.37-1.73]; combined P=2.58 · 10(-13)). A meta-analysis, using other in silico/de novo genotyping data for a total of 21 714 subjects, resulted in an overall odds ratio of 1.34 (95% CI: 1.25-1.44; P=1.032 · 10(-14)). The quantitative analysis on a population-based sample revealed an effect size of 1.91 (95% CI: 0.16-3.66) for systolic and 1.40 (95% CI: 0.25-2.55) for diastolic blood pressure. We identified in silico a potential binding site for ETS transcription factors directly next to rs3918226, suggesting a potential modulation of endothelial NO synthase expression. Biological evidence links endothelial NO synthase with hypertension, because it is a critical mediator of cardiovascular homeostasis and blood pressure control via vascular tone regulation. This finding supports the hypothesis that there may be a causal genetic variation at this locus.

Figure 1. Local Manhattan plot for the NOS3 (endothelial NOS) region

Each circle represents a SNP, its y-coordinate is the −log10 association P value for hypertension, the x-coordinate represents the physical position on the chromosome (on build 36, hg18). When replication data was available the combined P value was used, otherwise the discovery P value. Circles are filled with colours according to the LD (r²) between the given SNP and the lead SNP (rs3918266, violet square). Blue line indicates the recombination rate. The second best hit with P value 2.46E-6 in discovery stage (named chr7:150,314,954 according to 1000 genome project) was imputed based on the 1000 Genomes haplotypes (release June 2010), its imputation quality was very high (r²-hat = 0.94). In validation stage the imputation quality was very low (r²-hat = 0.17).

Figure 2. Forest plot of meta-analysis between Hypergenes Discovery, Hypergenes Validation, ASCOT/AIBIII/NBS, BRIGHT, EPIC Turin, HYPEST and NORDIL/MDC studies

The squares and the horizontal lines correspond to the OR and 95% CI of each study, the size of squares is proportional to weights (also shown as percentage), the dotted red line and the diamond represent the overall combined OR and 95% CI.