Correlation between interleukin-6 promoter and C-reactive protein (CRP) polymorphisms and CRP levels with the Mainz Severity Score Index for Fabry disease

Objectives: Fabry disease is a multisystem disorder with phenotypic heterogeneity only partially explained by genotype. Elevated interleukin-6 (IL-6) plasma levels and C-reactive protein (CRP) serum levels are associated with increased risk and worse outcome of ischaemic events, a serious prognostic sign in Fabry disease. Methods: 56 patients (34 hemizygous males, 22 females; 5 children) were studied. A promoter polymorphism -174G>C of the IL-6 gene associated with serum IL-6 levels was compared with the Mainz Severity Score Index (MSSI) in patients with Fabry disease. CRP levels and polymorphism 1059 G>C were evaluated as markers of inflammation to ascertain the possibility of an inflammatory mechanism of IL-6. Nonparametric ANOVA, Fisher's exact, Bonferroni, and Hardy-Weinberg (HW) statistics were used. Results: Mean age of adults = 42 (range 26-58) years; 29 patients received enzyme therapy (ERT). Mean total MSSI=26.7 (range 14.2-39.2) points, i.e. moderate disease, but females were lower (total 23.4±12.6 vs 32.2±13.6). Controls but not patients were in HW equilibrium. Significant correlation existed between all sub-scores of the MSSI and IL-6 genotypes in females but only with three MSSI sub-scores for males. The IL-6 C/C genotype was significantly correlated with the neurological, general and total MSSI sub-scores, generally twofold higher. There were no statistically significant correlations with CRP levels/polymorphisms and MSSI sub-scores nor with IL-6 polymorphisms. CRP levels decreased after ERT in patients with IL-6 G/G or G/C genotypes but increased in patients with C/C (p=0.003). Conclusions: The prevalence of the IL-6 C allele significantly influences MSSI, i.e. clinical severity, especially in females. This is unrelated to IL-6 as a pro-inflammatory marker as demonstrated by lack of correlations with CRP levels and genotypes. IL-6 -174 polymorphic C allele may be a prognostic marker in Fabry disease, especially in females.