It could very well be that a significant portion of our patients have MAS, which can be defined as having five of the following eight features: fever, splenomegaly, peripheral blood cytopenia, hypertriglyceridemia and/or hyperfibrinogenemia, hemophagocytosis in bone marrow, spleen, lymph node of liver, diminished NK cell activity, high ferritin levels and elevated soluble CD35 [51]. This evidence concerns the gene CR1 and Hemophagocytosis.