Bluett J et al. – Results of genome–wide association studies of psoriasis and rheumatoid arthritis have been used to identify candidate genes for subsequent testing in psoriatic arthritis (PsA) and have led to the identification of additional susceptibility factors for PsA. Most show overlap with psoriasis, whereas the overlap with rheumatoid arthritis is less pronounced. However, two loci show strong evidence for association with PsA but not psoriasis: HLA–B27 and the IL–13 gene locus.

• There is convincing evidence to suggest a strong genetic component to psoriatic arthritis (PsA), with studies reporting a 40–fold risk to first–degree relatives of patients with disease.
• However, compared with rheumatoid arthritis, the understanding of the genetic etiology of PsA is less well–developed.
• Only three modestly sized genome–wide association studies of PsA have been undertaken to date, but they have identified the HLA–C region, IL12B, TRAF3IP2, and FBXL19 genes as being associated with PsA susceptibility.