Polymorphisms in the PTPN22 region are associated with psoriasis of early onset

Background Psoriasis, a chronic inflammatory skin disease, affects approximately 2% of the population worldwide. Although the aetiology of psoriasis is poorly understood, patients with disease of early onset (Type I, age of onset <= 40 years) usually have a strong genetic component to the disease. Objectives The purpose of this study was to investigate the role of the protein tyrosine phosphatase nonreceptor type 22 (PTPN22) gene region in susceptibility to Type I psoriasis. Patients and methods Thirteen single nucleotide polymorphisms (SNPs) mapping to the PTPN22 region were genotyped in 647 patients with Type I psoriasis and 566 normal controls. Results The rs2476601 (R620W) SNP, widely associated with other inflammatory autoimmune diseases, showed no evidence of association with susceptibility to Type I psoriasis. Two SNPs (rs1217414 and rs3789604) demonstrated significant association with Type I psoriasis and were subsequently genotyped in a further 253 unrelated patients and 2024 normal controls. rs1217414 and rs3789604 were also significantly associated with Type I psoriasis in the combined datasets (P = 0.003 and P = 0.0002, respectively); furthermore carriage of both risk alleles was also significantly associated (P = 0.002). Conclusions This study demonstrates evidence of association of two SNPs (rs1217414 and rs3789604) in the PTPN22 region with Type I psoriasis, providing evidence for a role of this gene in Type I psoriasis that is not conferred by the R620W variant previously associated with a number of inflammatory diseases.