CD40LG and selective IgA deficiency disease: As stated by the European Society for Immunodeficiencies (ESID), the criteria for the definitive diagnosis of SIgAD include patients greater than 4 years of age who have serum IgA levels of less than 7 mg/dL (0.07 g/L) but normal serum IgG and IgM (also defined as isolated IgA deficiency), where other causes of hypogammaglobulinemia have been excluded, and there is normal IgG antibody response to vaccination.