Interleukin-6 gene polymorphism in Iranian patients with systemic lupus erythematosus

Interleukin 6 (IL-6) has been shown to be related to the pathogenesis of systemic lupus erythematosus (SLE). In the present study, the relationship between two polymorphisms in the promoter region of IL-6 gene at positions -572 G/C and -174 G/C and disease susceptibility in 401 Iranian patients with SLE was investigated using polymerase chain reaction-restriction fragment length polymorphism method. The genotype distribution and allele frequencies of IL-6 gene polymorphism at -174 position showed no significant difference between SLE patients and controls. In contrary, both allelic and genotypic frequencies at the -572 position significantly differed in SLE patients and controls. At this position, GG genotype was observed in 77.9% of patients compared to 68.9% in the control group (p < 0.014). The frequency of -572 G allele in patients (87.3%) was also higher than in controls (83.2%; p = 0.034). The haplotype study showed no significant difference between patients and healthy subjects. Study of the relationship between these polymorphisms and clinical manifestations and laboratory parameters showed an association between -174 polymorphism and the presence of antinuclear antibodies in all patients and rash and hematuria in male patients (p < 0.04). At -572 polymorphism, a significant difference with regard to photosensitivity in male patients (p = 0.04) was found. In conclusion, results of this study showed that -572 polymorphism plays an important role in susceptibility to SLE and that -174 polymorphism could influence the presence of antinuclear antibodies in the patients.