Similarly, monoallelic mutations in STXBP2 and LYST have been reported to occur with significantly greater frequency in patients with systemic juvenile idiopathic arthritis (sJIA) who develop clinical manifestations of HLH relative to those patients with sJIA who do not show signs of hyperinflammation (49). This evidence concerns the gene STXBP2 and systemic-onset juvenile idiopathic arthritis.