Exploring ankylosing spondylitis-associated ERAP1, IL23R and IL12B gene polymorphisms in subphenotypes of psoriatic arthritis.

OBJECTIVE To ascertain whether AS-associated polymorphisms of ERAP1, IL23R and IL12B genes associate with subphenotypes of PsA, particularly axial radiographic disease once stratified by HLA-B27 and HLA-Cw*0602 status. METHODS rs30187 (ERAP1 gene), rs6887695 (IL12B gene), rs11209026 and rs7530511 (IL23R gene) single nucleotide polymorphisms were genotyped in 263 PsA cases from a prospective cohort and compared with data from healthy controls (n = 3266-5422). ERAP1 results were stratified according to HLA-B27 and HLA-Cw*0602 status. Investigation of association with age at onset of psoriasis/PsA, arthritic joint count, axial radiographic disease, peripheral radiographic erosions, Psoriasis Area Severity Index, nail score and HAQ was made. RESULTS There was a strong association between rs6887595 (IL12B) and PsA, with homozygosity for the major allele being more frequent in PsA than controls (odds ratio 1.70; 95% CI 1.3, 2.2; P < 0.001). A trend was demonstrated for the minor allele of rs11209026 (IL23R) to be less frequent in patients with erosive joint disease than in those without erosions or controls (7%, 14% and 12%, respectively). None of the polymorphisms associated with the presence of axial radiographic disease or other clinical parameters. CONCLUSION We have confirmed a strong association between rs6887595 (IL12B) and PsA. A trend has been demonstrated between an IL23R variant and peripheral erosive disease. ERAP1 was not associated with axial radiographic disease in PsA. Spinal involvement in PsA may be genetically different from that in AS, which is in keeping with previous observations that the clinical and radiographic pattern of axial disease also differs.