The sample size used in the discovery cohort was selected based on its power to detect effect sizes equivalent to the confirmed JIA susceptibility causal variant within the PTPN22 gene, but we attempted to increase the power by selecting more homogeneous JIA cases, excluding systemic-onset JIA, psoriatic JIA, and enthesitis-related JIA cases. Here, PTPN22 is linked to systemic-onset juvenile idiopathic arthritis.