| Summary: | Aim: Most of the patients with Psoriatic Arthritis (PsA) develop arthritis following the onset of psoriasis. The aim of the project is to identify genetic and environmental risk factors for PsA among psoriasis patients.
Methods: PsA and psoriasis patients from two prospective cohorts were analyzed. The incidence of PsA among a prospective cohort of psoriasis patients was assessed. The distribution of Human Leukocyte Antigen (HLA) alleles and Killer Cell Immunoglobulin like Receptors (KIRs) and their combinations was compared between PsA, psoriasis and healthy controls. In addition, the association between a wide range of environmental exposures and PsA was evaluated by comparing the frequencies of exposed individuals among patients with recent onset PsA and psoriasis. The association between smoking and PsA was further investigated. The prevalence of smoking was in PsA, psoriasis and the general population. The interaction between HLA-C*06 and smoking was also tested.
Results: The genetic analysis revealed several HLA-B alleles and HLA haplotypes that are associated with PsA compared to psoriasis and can potentially serve as independent markers for PsA. Furthermore, several combinations of KIR genes and their respective HLA ligands were also found to be associated with PsA compared to psoriasis. The incidence of PsA among psoriasis patients was found to be higher than previously reported and its rate was constant over time. HLA-C*06 was associated with increased interval between psoriasis onset and PsA. Several environmental factors including occupational exposures, infections, injuries and smoking were associated with development of PsA. The prevalence of smoking was decreased among PsA patients compared to psoriasis. The interaction between HLA-C*06 and smoking was found to be significant.
Conclusions: Genetic and environmental factors are associated with the development of PsA in patients with psoriasis. These factors may serve as specific markers to identify psoriasis patients at increased risk for PsA.
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