There is a large body of evidence that there are the possible interactions among selected single nucleotide polymorphisms (SNPs) in genes associated with systemic inflammation reaction [1,2]. In this context, plasma levels of systemic inflammation biomarkers might be extremely variable depending on immune phenotypes of cells (CD8dim, GZB+, CD13+ and CD56+) that are involved into immunecompromised state and regulate producing of pro-inflammatory cytokines, such as C-reactive protein (CRP) [3]. CRP blood level closely relates to CRP genetic variants (SNPs) and it could be a good candidate for personal biological marker of cardiovascular disease (CVD) because recent studies have yielded strong association of several CRP genetic variants with increased mortality risk in general population as well as in patients with established CVD (Table 1). Moreover, CRP SNPs suggest a possible role of the inflammatory system as link between CVD risk factors and poor prognosis [3,4].

Table 1: The controversial results of CRP SNPs in prediction of CVD; CRP: C-Reactive Protein; CVD: Cardiovascular Disease; SNPs: Single Nucleotide Polymorphism.

CRP is predominantly secreted by the liver and adipose tissues in response to inflammatory stress and is predominantly regulated by interleukin [IL]-6 and some chemokine produced by wide spectrum of immune cells. Despite SNP CRP rs1205 polymorphism associated with circulating plasma CRP levels and CVD susceptibility in some populations, there is evidence that several mutant alleles of IL-1 gene and IL-6 gene may promote an elevated level of CRP regardless of SNPs’ presentation in CRP gene [4].

Numerous clinical studies have revealed that SNPs in the CRP gene have associated with increased risk of cancer, atherosclerosis, diabetes mellitus, bowel disease, rheumatoid arthritis, psoriasis, obstructive pulmonary disease, periodontitis, nonalcoholic fatty liver disease and CVD [5-9]. However, CRP genotype mediated rather CRP levels at acute phase of inflammation than at constitutional levels beyond antigen stimulation that is one of intriguing fact explaining controversial results of numerous pre-clinical and clinical studies depicted this issue [10]. On the other hand, in healthy men and women the polymorphisms of CRP were found in mild-to-moderate association with the basal CRP levels. Whether SNPs in CRP genes are powerful individual predictor of CV disease and poor clinical outcomes in patients with established CV is not fully clear [11].

Current evidence confirmed that CV risk factors may correspond to CRP levels and thereby directly affect local inflammation especially in the plaques, sub-intima of vascular walls, kidney and adipose tissues. The average CRP level in plasma was significantly higher in the smokers, with the highest level found among those with the CRP rs1800947 CC genotype [12]. In Framingham Heart Study twelve clinical covariates (body mass index, diabetes mellitus, obesity, hypertension, heart failure, etc.) explained 26% of the individual variability in CRP level in the participants [13]. Moreover, triallelic SNP in CRP gene (C-->T-->A), located in the promoter sequence, explained 1.4% of total serum CRP variation, and haplotypes harboring the minor T and A alleles of the SNP were close associated with higher CRP level [13]. In meta-analysis performed by Zhu et al. [14] CRP rs3093059 (T>C) polymorphism was found as a marker of lowered risk of myocardial infarction, especially among Asian populations. However, similar associations were not observed in CRP rs1800947 (G>C) and rs2794521 (G>A) polymorphisms (all p>0.05) among both Asian and Caucasian populations [14]. González-Giraldo et al. [15] in meta-analysis of clinical trials did not find significant associations between SNPs in CRP gene reported as CRP-rs1800947 (5 studies) and CRP-rs1205 (3 studies) and a risk of ischemic stroke. In contrast, Kolz et al. [16] reported found two polymorphisms within the C-reactive protein (CRP ) gene rs1800947 and rs1205, of which the minor alleles were strongly associated with lower levels of C-reactive protein and increased survival after myocardial infarction. It has suggested that increased plasma levels of CRP were associated with higher rates of acute and/or recurrent coronary atherothrombotic events, while this was not found in stable coronary artery disease [17]. However, CRP has been reported in number of studies to be a risk factor for CV disease and to have prognostic impact in patients with coronary artery disease, although a genetic variation in CRP and risk of CV disease were related modestly. Probably, there is need to reassess the role of CRP variability as a biological marker in general population and discover novel indicators of the individual CV risk [18-20]. Future large clinical studies are required to identify additional genetic risk factors for CV disease in different populations.

In conclusion, inconsistent results in determination of the predictive role of SNPs in CRP gene as a biological marker of CV disease and CV events require more investigations. Probably, ethnic and race particularities are main factors contributing to higher individual variability in CRP concentrations in different population. Finally, it is concerned that SNPs in CRP gene are promising biomarkers for CV risk stratifications.