Adults with COVID-19- associated “cytokine storm” syndrome also had clinical and laboratory characteristics similar to familial hemophagocytic lymphohistiocytosis or macrophage activation syndromes, such as: elevations of serum ferritin levels, liver enzymes, soluble interleukin-2 (IL-2) (sCD25) receptor, D-dimer, clotting times (prothrombin time and activated thromboplastin time) and lactic dehydrogenase (LDH), thrombocytopenia and lymphopenia.5 The gene discussed is IL2; the disease is macrophage activation syndrome.