Genetic and environmental influences on stability and change in baseline levels of C-reactive protein: A longitudinal twin study

Background and aims: Cross-sectional twin and family studies report a moderate heritability of baseline levels of C-reactive protein (CRP), ranging from 0.10 to 0.65 for different age ranges. Here, we investigated the stability and relative impact of genetic and environmental factors underlying serum levels of CRP, using a longitudinal classical twin design. Methods: A maximum of 6201 female twins from the TwinsUK registry with up to three CRP measurements (i.e. visit 1 [V1], visit 2 [V2] and visit 3 [V3]) over a 10-year follow-up period were included in this study. Structural equation modeling was applied to dissect the observed phenotypic variance into its genetic and environmental components. To estimate the heritability of CRP as well as its genetic and environmental correlations across different time points, a trivariate model was used. Results: Natural log (ln) CRP levels significantly increased from V1 to V2 (p = 4.4 x 10(-25)) and between V1 and V3 (p = 1.2 x 10(-15)), but not between V2 and V3. The median (IQR) follow-up time between V1 and V3 was 9.58 (8.00-10.46) years. Heritability estimates for CRP were around 50% and constant over time (0.46-0.52). Additionally, adjustment for BMI did not meaningfully change the heritability estimates (0.49-0.51). The genetic correlations between visits were significantly smaller than one, ranging from 0.66 to 0.85. Conclusions: The present study provides evidence for stable heritability estimates of CRP of around 50% with advancing age. However, between-visit genetic correlations are significantly lower than 1, indicating emergence of new genetic effects on CRP levels with age. (C) 2017 Elsevier B.V. All rights reserved.