Background  Phenotypically diverse autoimmune conditions share common genetic susceptibility loci and underlying molecular pathways.

Objectives  By systematically searching for single nucleotide polymorphisms (SNPs) associated with another autoimmune disease, rheumatoid arthritis (RA), we aimed to elucidate novel genetic markers of psoriasis.

Methods  We investigated 18 SNPs, previously confirmed as being associated with RA, in a U.K. cohort of 623 patients with early-onset psoriasis (presenting before age 40 years), comparing them with 2662 control subjects.

Results  Our findings confirm the association of early-onset psoriasis with REL (rs13031237, = 0·0027). The minor allele of REL had opposing effects upon susceptibility to disease in patients with psoriasis and RA.

Conclusion  Similar exploration of additional autoimmune loci and fine mapping of such regions may provide further insight into the genetics and molecular pathophysiology of psoriasis.