Notably, three patients with sJIA and one patient with overlap syndrome (with features of juvenile dermatomyositis, systemic lupus erythematosus and sJIA) had a persistently abnormal CD107a test with negative genetic tests (Table 3), suggesting that this assay is not entirely specific for primary forms of HLH, and that this pathway could be involved in the pathogenesis of MAS in some patients. Here, LAMP1 is linked to macrophage activation syndrome.