CD40LG and agammaglobulinemia: The primary criteria for CVID diagnosis include: (a) low serum levels of IgG, IgA and/or IgM, greater than two standard deviations below the normal mean for the age; (b) absent isohemagglutinins and poor responses to vaccines (especially the polysaccharide ones); and (c) an exclusion of other defined causes of hypogammaglobulinemia and/or other types of IEI [7,10].