The Association of Interleukin 6 Receptor Gene Variant (Rs4129267) with Susceptibility to Ankylosing Spondylitis and Soluble IL-6 Receptor Level in Iranian Patients

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Objectives: Ankylosing spondylitis (AS) is an axial skeleton-related auto-inflammatory arthritis. Interleukin 6 (IL-6) and its receptor (IL-6R) play a role in the etiopathology of AS. The recent genome-wide association studies (GWASs) revealed that rs4129267; an intrinsic variant of IL6-R is associated with the risk of AS. We aimed to study the rs4129267 IL6R variant in Iranian AS patients and the correlation of this variant with the soluble interleukin-6 receptor (sIL-6R) serum level. Materials and Methods: In this case-control study, we genotyped rs4129267 IL6-R variant in extracted DNA from 498 AS patients and 495 matched healthy controls by Amplification-Refractory Mutation System Polymerase Chain Reaction (ARMS-PCR). The serum level of sIL-6R and IL-6 was also analysed in 39 controls and 42 AS patients by the ELISA method. The correlation between rs4129267 IL-6R variants and patients’ clinical manifestations and sIL-6R level was also investigated. Results: In comparison to the AS individuals, C allele were significantly less prevalent in the healthy control group (OR = 1.23 [1.01 –1.48], P value = .034). Patients had significantly elevated levels of IL-6 serum levels. There was a significant correlation between the presence of the rs4129267 T allele and increased sIL-6R level. Conclusions: Our study confirmed the significant association between the rs4129267 T variant and the protection against AS disease susceptibility. Increased IL-6 level and reduced frequency of sIL-6R rs4129267 T allele in patients which contributes to reduced sIL-6R serum level, highlights the significant role of IL-6 signalling pathway in AS pathogenesis.