['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<or=40 years) usually have a strong genetic component to the disease.', '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.', 'Thirteen single nucleotide polymorphisms (SNPs) mapping to the PTPN22 region were genotyped in 647 patients with Type I psoriasis and 566 normal controls.', '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).'] Are polymorphisms in the PTPN22 region associated with psoriasis of early onset?