Interleukin-6 gene polymorphism and faster progression to end-stage renal failure in chronic glomerulonephritis

Interleukin-6 (IL-6) is a multifunctional cytokine produced by different cell types, including monocytes, lymphocytes, endothelial and mesangial cells. Deregulated production of IL-6 was found to be involved in mesangial proliferative glomerulonephritis. We investigated whether the single nucleotide polymorphism (SNP) in the promoter region of the IL-6 gene is associated with a development of chronic glomerulonephritis (CGN). The study group consisted of 541 patients with CGN. Of those 338 already progressed to ESRD. The control group involved 253 healthy individuals. All subjects were genotyped for the -634 C/G polymorphism of the IL-6 gene by polymerase chain reaction (PCR). PCR product was digested with BsrBI restriction endonuclease and analyzed on 3% agarose. The allele and genotype frequencies were similiar between CGN patients in a pre-dialysis stage and control subjects. Significantly increased frequency of the G allele was observed in the ESRD patients (13% vs. 6% in pre-dialysis stage, P < 0.01). After dividing ESRD patients according to time from reported disease onset to ESRD, those with time ≤5 years showed even higher G allele frequency (21% vs. 13% in entire ESRD group). Interestingly, most of the GG homozygotes were in this faster progressing group. Both subgroups were comparable for sex, age, BMI, total cholesterol and serum creatinine. The multivariate logistic regression analysis revealed that the IL-6 genotype with the G allele was an independent risk factor of progression to ESRD (P < 0.001). Our results indicate that the IL-6 -634 G/C polymorphism may be a possible risk factor for faster progression of chronic glomerulonephritis to ESRD. It is also possible that this polymorphism is in linkage disequilibrium with another functional polymorphism in the II-6 gene or its vicinity.