To the editor:

Thrombin is central not only in procoagulatory processes like fibrinogen or platelet activation but also in other systems that are related to inflammation control.1  Recently, Flick et al characterized inflammatory responses of transgenic prothrombin mutant (F2WE) mice in a collagen-induced arthritis (CIA) model.2  Mice carrying the F2WE transgene that has dramatically reduced procoagulatory effects on fibrinogen and protease-activated receptor 1 exhibited a significantly attenuated inflammatory joint disease in CIA.

Prothrombin 20210G>A (F220210G>A) is a gain-of-function variant resulting in increased prothrombin expression and elevated risk of venous thromboembolic events (VTE).3  Based on the data of Flick et al2  we hypothesized that F220210G>A is associated with increased inflammatory responses, and we tested this hypothesis in a cohort with longitudinal measurements of C-reactive protein (CRP) levels. Study population consisted of 565 women [age, median (interquartile range), 32 years (28-36)] with 2.258 observations [observations per patient: 2 (n = 153), 3 (n = 109), 4 (n = 98), 5 (n = 86), > 5 (n = 119)] followed during pregnancy predominantly because of history of fetal loss, placental dysfunction or VTE. Pregnancy is known as a mild proinflammatory condition with moderately elevated CRP levels.4  These are increased further in case of disturbed placentation or other pregnancy complications.5  An association between CRP levels and risk of VTE has been described previously, as well.6  To adjust for intra-individual CRP level variations evaluation was restricted to patients with CRP levels of at least 2 independent times of presentation.7  Therefore, for univariate and multivariate analyses as well as nonparametric comparisons robust clustered estimates of variances were calculated to allow for intracluster correlation and to relax requirement for independent observations (Stata 10.1 Macintosh, StataCorp). F220210G>A genotypes were characterized as described,8  plasma CRP levels were quantified by an immunoturbidimetric method standardized according to International Federation of Clinical Chemistry and Laboratory Medicine (Roche Diagnostics). The study was approved by the local ethics committee. All individuals were included in this study, after informed consent had been provided.

Carrier frequency of F220210A was 5.5%. Carriers of the F220210A variant exhibited significantly more frequently CRP elevations (≥ 5 mg/L, 47.5% [65/137 observations], ≥ 10 mg/L, 25.6% [35 of 137 observations], ≥ 15 mg/L, 11.7% [16 of 137 observations]) compared with F220210GG wild-type individuals (≥ 5 mg/L, 30.7% [650/2121 observations], ≥ 10 mg/L, 10.3% [219 of 2121 observations], ≥ 15 mg/L, 4.8% [101 of 2121 observations] Table 1). CRP levels (mean CRP level [95% CI] were significantly higher in carriers of F220210A (0.75 mg/L [0.63-0.87]) than in individuals with the corresponding wild-type (0.54 mg/L [0.52-0.57]; Mann-Whitney U test, P < .0001, Padj < .05).

Table 1

Association of F220210G>A genotype with CRP levels

CRPCarriage of F220210A versus F220210GG
Univariate
Multivariate
OR95% CI (P)95% CI (P)*OR95% CI (P)95% CI (P)*
≥ 5 mg/L 2.04 1.44-2.89 (< .0001) 1.12-3.72 (< .02) 1.91 1.32-2.75 (< .0005) 1.00-3.67 (.05) 
≥ 10 mg/L 2.99 1.98-4.48 (< 10−61.49-5.98 (.002) 3.21 2.11-4.88 (< 10−71.61-6.37 (< .001) 
≥ 15 mg/L 2.64 1.51-4.62 (< .001) 1.18-5.93 (< .02) 2.86 1.62-5.06 (< .0005) 1.29-6.34 (< .01) 
CRPCarriage of F220210A versus F220210GG
Univariate
Multivariate
OR95% CI (P)95% CI (P)*OR95% CI (P)95% CI (P)*
≥ 5 mg/L 2.04 1.44-2.89 (< .0001) 1.12-3.72 (< .02) 1.91 1.32-2.75 (< .0005) 1.00-3.67 (.05) 
≥ 10 mg/L 2.99 1.98-4.48 (< 10−61.49-5.98 (.002) 3.21 2.11-4.88 (< 10−71.61-6.37 (< .001) 
≥ 15 mg/L 2.64 1.51-4.62 (< .001) 1.18-5.93 (< .02) 2.86 1.62-5.06 (< .0005) 1.29-6.34 (< .01) 

Analyses based on 565 patients and 2258 observations. Multivariate analyses were adjusted for weeks of gestation, age and ethnicity.

F220210A indicates carriage of prothrombin 20210A variant; F220210GG, prothrombin 20210GG wild-type; OR, odds ratio; and CI, confidence interval.

*

95% CI and P value after adjustment for nonindependent observations within clusters.

The F220210G>A genotype is known to influence prothrombin expression.3  In our study population prothrombin levels (mean prothrombin activity [95% CI]) were assessed in 122 patients and were significantly increased in F220210A carriers compared with (F220210GG wild-types F220210GG, 112% [109-115], F220210A, 138% [111-166], t test, P = .0005). Thus, our finding that the gain-of-function variant F220210A is associated with increased CRP levels further corroborates the assumption of Flick et al that (pro)thrombin positively is involved in inflammatory processes and that targeting (pro)thrombin activity could have the potential to modulate inflammatory disease processes.2 

Acknowledgments: This work was supported by the German Federal Ministry of Education and Research through ArthroMark (grant 01EC1009A). B.H. had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Contribution: B.H. developed the hypotheses, and conceived and designed the study; T.H. and B.H. coordinated sample acquisition and laboratory analyses and analyzed the data; G.R.B., T.H. and B.H. interpreted the data; B.H. drafted the manuscript; and G.R.B. and T.H. critically revised the manuscript for important intellectual contents. All authors had full access to all data and approved the final version of the manuscript.

Conflict-of-interest disclosure: The authors declare no competing financial interests.

Correspondence: Dr Berthold Hoppe, Institute of Laboratory Medicine, Clinical Chemistry and Pathobiochemistry, Charité – Universitätsmedizin Berlin, Campus Charité Mitte, Charitéplatz 1, 10117 Berlin, Germany; e-mail: berthold.hoppe@charite.de.

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