Background: Metabolic syndrome has been suggested to have an association with C-reactive protein (CRP), a biomarker of cardiovascular disease risk. Given that genetic factors influence both metabolic syndrome and CRP, it seems necessary to examine the association with consideration of genetic influence.
Methods: We conducted a cross-sectional study and a co-twin-control study in 2555 Korean adults composed of twins and their family members. For the co-twin-control study, 113 pairs of monozygotic twins who were discordant in regard to CRP level (>0.5 mg/L) were selected. Cross-trait additive genetic correlation between CRP and metabolic syndrome and the risk for having higher CRP level associated with components of metabolic syndrome were estimated.
Results: With increasing CRP level, the prevalence of metabolic syndrome increased linearly. Among components of metabolic syndrome, high-density lipoprotein cholesterol (HDL-C) was inversely associated with CRP, whereas other components were positively associated. Most of the components of metabolic syndrome except for HDL-C had a significant genetic correlation with CRP, with the highest correlation for obesity indices. A co-twin-control study that allows full control of genetic influence showed that only obesity was significantly associated with higher CRP levels: Odds ratios (95% confidence intervals) were 1.23 (1.04,1.46) for 1 kg/m(2) increase in body mass index and 1.12 (1.03,1.22) for 1% increased in total body fat, respectively.
Conclusions: Although genetic influence played a significant role in the associations between CRP and most metabolic syndrome components, environmental influence that may be modifiable also contributed to the association, especially to the associations between the obesity indices and CRP.