CD40LG and agammaglobulinemia: Since 1999, according to Pan-American Group for Immunodeficiency (PAGID) and European Society for Immunodeficiencies (ESID), SIgAD is diagnosed in an individual older than 4 years with serum IgA level <7 mg/dL but a normal IgG and IgM serum level and with the exclusion of other causes of hypogammaglobulinemia, as well as with the normal response to vaccinations [22].