Some functional protein-coding single nucleotide polymorphisms (SNPs) have been identified in genes associated with AS, such as HLA-B, ERAP1 and IL23R. 1–4 More commonly, the associated SNPs lie in non-coding flanking sequences or intragenic regions where they may influence gene expression.1, 2, 5 Genome-wide association studies (GWAS) show convincing association between RUNX3 and AS and psoriatic arthritis, another form of SpA.1, 2, 6 This association extends to a cluster of SNPs at the RUNX3 locus,1 located from 0.5 to 2 kb upstream of the RUNX3 promoter. This evidence concerns the gene RUNX3 and psoriatic arthritis.