In two siblings with systemic JIA was found a homozygous mutation in the FAMIN gene also involved in the immune system regulation and promotion of oxidative stress [12] and a functional intronic variant in UNC13D disrupting an NF-κB enhancer was reported in a patient with systemic JIA and recurrent macrophage activation syndrome (MAS) [13]. This evidence concerns the gene UNC13D and macrophage activation syndrome.