Compared to SJIA patients without MAS, the KFD group had a significantly higher serum IFN-γ level (p = 0.006) and IFN-γ/IL-6 ratio (p = 0.0003), and much lower levels of serum IL-6 (p = 0.007) and IL-2 (p = 0.016). The gene discussed is IFNG; the disease is macrophage activation syndrome.