Genetic and environmental contributions to plasma C-reactive protein and interleukin-6 levels--a study in twins.

Elevated baseline levels of acute-phase proteins such as C-reactive protein (CRP) or cytokines like interleukin-6 (IL-6) are known risk factors for atherosclerosis and cardiovascular disease (CVD) events. However, until today, there is only controversial information about the contribution of genetic and environmental factors. Therefore, we performed an open prospective study in 108 monozygotic (MZ) and 60 same-sex dizygotic (DZ) twin pairs to analyse the genetic and environmental contributions to plasma CRP and IL-6 levels. Heritability of IL-6 was 0.61, indicating that plasma IL-6 levels are to a major part influenced by genetic determinants; however, for CRP, heritability was only 0.22, pointing to a moderate genetic influence. Plasma CRP levels were strongly influenced by female gender, older age and especially the body mass index. Our data underline the central role of IL-6 in low-grade inflammation contributing to atherosclerosis and CVD.