FTH1 and macrophage activation syndrome: Hyperferritinemia is a common feature shared by both AOSD and MAS.[13] It has been reported that it is not only a diagnostic marker of AOSD,[14] but also a prognostic marker of MAS.[9] It independently associated with severity of the clinical manifestations of AOSD[15] and MAS-related death.[16] Ferritin is not only considered as a consequence of the inflammation but also thought to be involved in pathogenic mechanisms.[13,17] The inflammatory cytokines stimulate macrophages to release H-ferritin, the heavy subunit of ferritin, via Fer2 activation.