title: Evidence to support IL-13 as a risk locus for psoriatic arthritis but not psoriasis vulgaris.
abstract: OBJECTIVE
  There is great interest in the identification of genetic factors that differentiate psoriatic arthritis (PsA) from psoriasis vulgaris (PsV), as such discoveries could lead to the identification of distinct underlying aetiological pathways. Recent studies identified single nucleotide polymorphisms (SNPs) in the interleukin 13 (IL-13) gene region as risk factors for PsV. Further investigations in one of these studies found the effect to be primarily restricted to PsA, thus suggesting the discovery of a specific genetic risk factor for PsA. Given this intriguing evidence, association to this gene was investigated in large collections of PsA and PsV patients and healthy controls.
  
  
  METHODS
  Two SNPs (rs20541 and rs1800925) mapping to the IL-13 gene were genotyped in 1057 PsA and 778 type I PsV patients using the Sequenom genotyping platform. Genotype frequencies were compared to those of 5575 healthy controls. Additional analyses were performed in phenotypic subgroups of PsA (type I or II PsV and in those seronegative for rheumatoid factor).
  
  
  RESULTS
  Both SNPs were found to be highly associated with susceptibility to PsA (rs1800925 ptrend = 6.1 × 10(-5) OR 1.33, rs20541 ptrend = 8.0 × 10(-4) OR 1.27), but neither SNP was significantly associated with susceptibility to PsV.
  
  
  CONCLUSIONS
  This study confirms that the effect of IL-13 risk locus is specific for PsA, thus highlighting a key biological pathway that differentiates PsA from PsV. The identification of markers that differentiate the two diseases raises the possibility in future of allowing screening of PsV patients to identify those at risk of developing PsA.
authors.affiliation: Arthritis Research UK Epidemiology Unit, Manchester Academic Health Science Centre, The University of Manchester, Manchester, UK.
authors.forename: John
authors.initials: J
authors.lastname: Bowes
authors.forename: Steve
authors.initials: S
authors.lastname: Eyre
authors.forename: Edward
authors.initials: E
authors.lastname: Flynn
authors.forename: Pauline
authors.initials: P
authors.lastname: Ho
authors.forename: Salma
authors.initials: S
authors.lastname: Salah
authors.forename: Richard B
authors.initials: RB
authors.lastname: Warren
authors.forename: Helena
authors.initials: H
authors.lastname: Marzo-Ortega
authors.forename: Laura
authors.initials: L
authors.lastname: Coates
authors.forename: Ross
authors.initials: R
authors.lastname: McManus
authors.forename: Anthony W
authors.initials: AW
authors.lastname: Ryan
authors.forename: David
authors.initials: D
authors.lastname: Kane
authors.forename: Eleanor
authors.initials: E
authors.lastname: Korendowych
authors.forename: Neil
authors.initials: N
authors.lastname: McHugh
authors.forename: Oliver
authors.initials: O
authors.lastname: FitzGerald
authors.forename: Jonathan
authors.initials: J
authors.lastname: Packham
authors.forename: Ann W
authors.initials: AW
authors.lastname: Morgan
authors.forename: Christopher E M
authors.initials: CE
authors.lastname: Griffiths
authors.forename: Ian N
authors.initials: IN
authors.lastname: Bruce
authors.forename: Jane
authors.initials: J
authors.lastname: Worthington
authors.forename: Anne
authors.initials: A
authors.lastname: Barton
mesh_terms: D000328:Adult; D017668:Age of Onset; D015535:Arthritis, Psoriatic / Q000235:genetics* / Q000276:immunology; D016022:Case-Control Studies; D005787:Gene Frequency; D020022:Genetic Predisposition to Disease; D005838:Genotype; D006801:Humans; D018793:Interleukin-13 / Q000235:genetics*; D020641:Polymorphism, Single Nucleotide; D011565:Psoriasis / Q000235:genetics; D012217:Rheumatoid Factor / Q000097:blood
chemical_list: D018793:Interleukin-13; D012217:Rheumatoid Factor