S100A9 and juvenile idiopathic arthritis: Several biomarkers (S100, S100A8, S100A9, and S100A12 proteins) have been associated with various aspects of systemic manifestations of Juvenile Idiopathic Arthritis (JIA), in predicting the phenotype, severity, and progression of the disease, for predicting flare of the disease, higher risk of poor response to methotrexate treatment (two single nucleotide polymorphisms or SNPs in the ATIC gene and one SNP in ITPA gene), predicting response to treatment (S100), and disease relapse (high S100A12 and MRP8/14) with six months of discontinuing treatment (65).