UNC13D and macrophage activation syndrome: The first case of association of s-JIA and FHL-related genes was reported by Hazen et al. in 2008, who described an 8-year-old girl with s-JIA and hemophagocytosis, without complete criteria of MAS, who was found to have compound heterozygous mutations of UNC13D and reduced NK cell cytotoxic function (135).