Genetics [315–318]

Background: Psoriatic arthritis (PsA) is a complex inflammatory arthritis with strong genetic component as suggested by family studies. Clinically, it shows overlap with ankylosing spondylitis as sacroiliitis is a feature of both diseases. Genome wide association studies have identified a single nucleotide polymorphism (SNP) at the ERAP1 locus that is associated with disease susceptibility in ankylosing spondylitis. The aim of the study was to determine if the same SNP was associated with psoriatic arthritis in the Caucasian population of UK. Methods: DNA samples were available from 911 UK cases with PsA, defined as an inflammatory arthritis associated with psoriasis. The ERAP1 SNP (rs30187) was genotyped in the DNA samples using the Sequenom MassARRAY platform. The PLINK software package (http://pngu.mgh.harvard.edu/purcell/plink/) was used to compare genotype and allele frequencies between PsA cases and data available for the same SNP in 3775 UK controls from the Wellcome Trust Case Control Consortium (WTCCC). Stratification analysis was undertaken to investigate whether effect sizes differed by gender or type of psoriasis (type 1 psoriasis = age at onset