['This study aimed to identify polymorphic variants of the Periostin gene associated with disease severity and clinical course in children with juvenile idiopathic arthritis.', 'DNA genotyping of 7 single-nucleotide polymorphisms within the periostin gene was performed in 117 patients and their parents and in 102 control samples. Our patients were divided in the following 4 disease categories: 1) persistent oligoarthritis; 2) extended oligoarthritis; 3) polyarthritis; 4) systemic arthritis. Quantitative association analysis was performed in order to test for association between the 7 genetic variants and 18 selected clinical traits.', 'A harmful association was observed between the minor allele of rs17197936 and 2 clinical traits, count of joints with active arthritis and count of joints with pain on motion/tenderness, in patients with extended oligoarthritis. Furthermore, the haplotype represented by the minor allele variants of rs3829364, rs6750 and rs9547951 showed an unfavourable association with the above 2 traits plus the following 3 in the whole patient group: juvenile arthritis damage index articular score, childhood health assessment questionnaire score and disease duration.'] Are periostin gene variants associated with disease course and severity in juvenile idiopathic arthritis?