Interleukin 18 (-137G/C, -607C/A) Polymorphisms as Genetic Biomarkers of Susceptibility to Systematic Lupus Erythematosus

Abstract

Background: Systemic lupus erythematosus (SLE) is an autoimmune disease of unknown etiology. Several studies have suggested that interleukin-18 (IL-18) is associated with SLE pathogenesis. The genotype distribution of IL-18 promoter polymorphisms differs among ethnic populations. The present study aimed to investigate the correlation between IL-18 polymorphisms at positions -137 and -607 in patients situated in Northeastern Iran. Methods: This case-control study examined the prevalence of IL-18 -137C/G and -607C/A polymorphic variants among 95 SLE patients referred to the Department of Rheumatology, who were referred to the general clinics of Ghaem Hospital and Imam Reza Hospital in Mashhad, Iran, were included in the study. In addition, 100 healthy individuals were included in the control group. DNA from whole blood was extracted by the salting-out method using a commercial kit (Biogene, US). Allelic and genotypic frequencies of polymorphisms (-137G/C, -607C/A) in the IL-18 promoter gene were analyzed using a polymerase chain reaction (PCR)-based amplification refractory mutation system (ARMS) method. Results: The results of this study demonstrated that the frequency of SLE patients with the homozygous C/C genotype of the IL-18 promoter gene at position -137 was significantly higher than that of the homozygous G/G genotype (P < 0.001) in normal controls. Furthermore, the polymorphism analysis performed illustrated a significant association between (-137G/C) and (-607C/A) polymorphisms in the IL-18 promoter gene and SLE (P < 0.005). Conclusion: These results indicated that the 607A/A and 137C/C polymorphisms are more prevalent in SLE. Further research involving larger sample sizes from various populations is necessary to elucidate the role of these polymorphisms and the distribution of alleles in SLE patients.