The causal effect of interleukin-17 on the risk of psoriatic arthritis: a Mendelian randomization study.

Objective To determine causal associations between genetically predicted TNF-α, IL-12p70 and IL-17 levels and risk of PsA. Methods The publicly available summary-level findings from genome-wide association studies (GWAS) was used to identify loci influencing normal physiological concentrations of TNF-α, IL-12p70 and IL-17 (n  = 8293) among healthy individuals as exposure and a GWAS for PsA from the UK Biobank (PsA = 900, control = 462 033) as the outcome. A two-sample Mendelian randomization (MR) analysis was performed using the inverse-variance weighted (IVW), weighted median and MR–Egger regression methods. Sensitivity analysis and MR–Egger regression analysis were performed to evaluate the heterogeneity and pleiotropic effects of each variant. Results Single-nucleotide polymorphisms (SNPs) at genome-wide significance from GWASs on TNF-α, IL-12p70 and IL-17 were identified as the instrumental variables. The IVW method indicated a causal association between increased IL-17 level and risk of PsA (β = −0.00186 per allele, s. e. = 0.00043, P  = 0.002). Results were consistent in the weighted median method (β = −0.00145 per allele, s. e. = 0.00059, P  = 0.014) although the MR–Egger method suggested a non-significant association (β = −0.00133 per allele, s. e. = 0.00087; P  = 0.087). Single SNP MR results revealed that the C allele of rs117556572 was robustly associated with risk of PsA (β = 0.00210, s. e. = 0.00069, P  = 0.002). However, no evidence for a causal effect was observed between TNF-α, IL-12p70, decreased IL-17 levels and risk of PsA. Conclusion Our findings provide preliminary evidence that genetic variants predisposing to higher physiological IL-17 level are associated with decreased risk of PsA. [ABSTRACT FROM AUTHOR]

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