It has been shown, both in XLP-1 patients and in SAP-deficient mice models, that the absence of SAP is responsible for an immunodeficiency that is due to an absence of NKT cell development, a decrease in B cell functions and a reduced T-cell and NK-cell cytotoxic activities [7], [18], [19], [20]. The gene discussed is SH2D1A; the disease is immune system disorder.