Association of IL-18 gene polymorphism (-137C) with arthritis manifestations in SLE: combined effect with IFN gamma gene polymorphism (+874A)

We analyzed the association between single nucleotide polymorphisms in IL-12 and IL-18 genes in disease susceptibility and severity of SLE in Thais. A weak association was observed between A allele of the IL-12 gene at the 3' untranslated region in SLE patients with proteinuria (OR = 1.89, 95% CI = 1.05-3.40, P = 0.02, Pc = 0.06). In addition, we found a significant association between C allele of IL-18 (-137) with arthritis (OR = 6.88, 95% CI = 1.54-42.93, P = 0.003, Pc = 0.009). The presence of one C allele (C/C+C/G) was associated with significant OR of 8.72 (95% CI = 1.83-56.71, P = 0.001, Pc = 0.003). Interestingly, we found the combined effect between the G/C genotype of IL-18 (-137) and the A/A genotype of IFNG (+874) gene causing susceptibility of arthritis in SLE patients (OR = 13.22, 95% CI = 1.56-291.66, P = 0.004).