CD40LG and selective IgA deficiency disease: In cases where IgM and IgG levels are normal and there is no other cause of hypogammaglobulinemia, the isolated IgA deficiency is defined as selective immunoglobulin a deficiency (SIgAD), which is the most common primary immunodeficiency and have a significant association with mucosal infection, increased risks of atopic disease, and a higher prevalence of autoimmune disease (43).