The diagnoses of CVID can be made if the followings are fulfilled: decreased srum level of IgG (at least two standard below the mean), and marked decrease in IgA, with or without low IgM, inability to produce protective level of specific antibodies, especially IgG, secondary causes of hypogammaglobulinemia have been excluded such as malignancies and exclusion of other primary immunodeficiencies. Here, CD40LG is linked to agammaglobulinemia.