Evidence for common genetic control in pathways of inflammation for Crohn's disease and psoriatic arthritis

Abstract Objective Clinical, pharmacologic, and epidemiologic evidence supports the hypothesis that common genetic pathways may underlie inflammatory diseases. In a previous study, a Crohn's disease gene, CARD15 , was demonstrated to be associated with psoriatic arthritis (PsA). Recently, a functional haplotype of 2 single‐nucleotide polymorphisms (SNPs) mapping to the organic cation transporter ( OCTN ) genes, SLC22A4 and SLC22A5 , was identified as a second Crohn's disease susceptibility locus. The SLC22A4 gene has also been associated with rheumatoid arthritis. This study was undertaken to further elucidate associations of PsA with Crohn's disease susceptibility genes. Methods Association with CARD15 and OCTN was investigated in UK Caucasian patients with PsA (n = 472) and population controls (n = 594), using 5′ allelic discrimination assays (TaqMan). Two SNPs in OCTN , forming a haplotype previously associated with Crohn's disease, were also tested in patients with psoriasis (n = 218) and patients with early undifferentiated inflammatory arthritis (n = 386). Allele and estimated haplotype frequencies were compared between patients and controls. Results No association of PsA with CARD15 was detected. In contrast, a functional SNP mapping to the promoter region of SLC22A5 (rs2631367) was associated with PsA (for CC versus GG, odds ratio 1.65, 95% confidence interval 1.13–2.41, uncorrected P = 0.005). In addition, the haplotype associated with Crohn's disease was also associated with PsA ( P = 0.001). No association was detected in the cohort with psoriasis alone or in the cohort with undifferentiated inflammatory arthritis. Conclusion The OCTN haplotype previously associated with Crohn's disease is also associated with PsA, suggesting that these 2 diseases may share some common genetic control in pathways of inflammation.