A total of 5,393 patients were included for model development, and predictor variables were age at JIA onset (hazard ratio [HR] 0.83 [95% confidence interval (95% CI) 0.77–0.89]), ANA positivity (HR 1.59 [95% CI 1.06–2.38]), and International League of Associations for Rheumatology category of JIA (HR for oligoarthritis, psoriatic arthritis, and undifferentiated arthritis versus rheumatoid factor–negative polyarthritis 1.40 [95% CI 0.91–2.16]). This evidence concerns the gene BTG3 and polyarticular arthritis.