A study to investigate whether single nucleotide polymorphisms (SNPs) mapping to locus 4 on chromosome 1q21, comprising two genes of the late cornified envelope gene cluster, are risk factors for psoriatic arthritis (PsA) in U.K. and Irish populations was undertaken. Three SNPs (rs4112788, rs4085613 and rs6701216) with prior evidence of association with psoriasis vulgaris (PsV) susceptibility were genotyped in 1,057 PsA patients and 5,575 healthy controls. No association with PsA was found with rs6701216. However, rs4112788 and rs4085613 were found to be enriched in cases compared with controls (69 vs. 65%, respectively), and significantly associated with increased PsA risk (P = 0.001). Thus these data suggest that locus 4 on chromosome 1q21 ...