C-Reactive Protein Levels and Risk of Cardiovascular Diseases: A Two-Sample Bidirectional Mendelian Randomization Study

Abstract

Elevated C-reactive protein (CRP) levels are an indicator of inflammation, a major risk factor for cardiovascular disease (CVD). However, this potential association in observational studies remains inconclusive. We performed a two-sample bidirectional Mendelian randomization (MR) study using publicly available GWAS summary statistics to evaluate the relationship between CRP and CVD. Instrumental variables (IVs) were carefully selected, and multiple approaches were used to make robust conclusions. Horizontal pleiotropy and heterogeneity were evaluated using the MR-Egger intercept and Cochran's Q-test. The strength of the IVs was determined using F-statistics. The causal effect of CRP on the risk of hypertensive heart disease (HHD) was statistically significant, but we did not observe a significant causal relationship between CRP and the risk of myocardial infarction, coronary artery disease, heart failure, or atherosclerosis. Our primary analyses, after performing outlier correction using MR-PRESSO and the Multivariable MR method, revealed that IVs that increased CRP levels also increased the HHD risk. However, after excluding outlier IVs identified using PhenoScanner, the initial MR results were altered, but the sensitivity analyses remained congruent with the results from the primary analyses. We found no evidence of reverse causation between CVD and CRP. Our findings warrant updated MR studies to confirm the role of CRP as a clinical biomarker for HHD.

Keywords: C-reactive protein; MR-PRESSO; Mendelian randomization; PhenoScanner; bidirectional Mendelian randomization analysis; cardiovascular diseases; hypertensive heart disease; multivariable MR analysis; sensitivity analysis; two-sample Mendelian randomization.

Figure 1

(A) Study design for the CRP-CVD two-sample bidirectional MR analyses. (B) The validity of the MR method depends on the instrumental variables (IVs) being satisfied for three key assumptions. Genetic instrumental variables were obtained for C-reactive protein levels from UK Biobank. GWAS summary statistics for CVD were obtained from FinnGen or EBI GWAS catalog. Two-sample MR analyses were performed for each exposure–outcome pair.

Figure 2

Candidate IV selection using quality control steps. We used two different approaches (Approach 1 and 2) to perform the two-sample MR study.

Figure 3

Causal associations between CRP levels and CVD using Approach 1. MR estimations were performed using IVW as the primary method and PWM and WM as sensitivity analyses. The effect sizes are shown by a black square with 95% confidence intervals as black dashed lines. The number of SNPs found in the outcome GWAS is shown in the #SNPs column. Abbreviations: cardiovascular diseases: CVD, inverse-variance weighted: IVW, weighted median: WM, penalized weighted median: PWM, 95% confidence interval: 95% CI.

Figure 4

Causal associations between CRP levels and CVD using Approach 2. MR estimations were performed using IVW as the primary method and PWM and WM as sensitivity analyses. The effect sizes are shown by a black square with 95% confidence intervals as black dashed lines. The number of SNPs found in the outcome GWAS is shown in the #SNPs column. Abbreviations: cardiovascular disease: CVD, inverse-variance weighted: IVW, weighted median: WM, penalized weighted median: PWM, 95% confidence interval: 95% CI.

Figure 5

Results from the multivariable MR study between CRP and HHD. The adjusted effect sizes are shown as black squares with 95% confidence intervals presented as black dashed lines.