AbstractObjectiveRecent reports have confirmed association of single‐nucleotide polymorphisms (SNPs) mapping to the interleukin‐23 receptor (IL‐23R) and IL‐12β genes with psoriasis susceptibility. The aim of this study was to determine whether these variants are also associated with susceptibility to psoriatic arthritis (PsA).MethodsTwo IL23R SNPs (rs7530511 and rs11209026) and 2 IL12B SNPs (rs3212227 and rs6887695) were genotyped in DNA samples from 520 white patients with PsA and 2,260 control subjects, all of whom resided in the UK. For SNP rs3212227, data on a larger group of controls (n = 4,681) were publicly available; this information was used in the analysis. Genotype counts were compared between patients with PsA and population controls, using the trend test.ResultsA haplotype comprising carriage of the common variants of both IL23R SNPs was associated with PsA susceptibility (adjusted P = 0.013 [1,000 permutations]). Both IL12B SNPs were independently associated with PsA susceptibility, and this association was strongest under a dominant model, with homozygosity for the common allele being more frequent in patients with PsA than in control subjects: for rs3212227, the odds ratio (OR) for carriage of AA versus other genotypes was 1.43 (95% confidence interval [95% CI] 1.17–1.76); for rs6887695, the OR for carriage of GG versus other genotypes was 1.43 (95% CI 1.18–1.74).ConclusionVariation within IL23R and IL12B is associated with susceptibility to both psoriasis and PsA. The effect sizes observed in patients with PsA appear to be smaller than those previously reported in patients with psoriasis, suggesting that both loci are primarily associated with psoriasis susceptibility. However, this does support the idea that the genetic etiology of the psoriasis present in patients with PsA has susceptibility loci in common with those observed in patients with uncomplicated psoriasis.