Patients with 18q deletion syndrome exhibit a deficiency in at least one of the immunoglobulins, IgA, M, G, E, and IgG1 − 4 in 88% of cases [2], with IgE deficiency being the most common (52%), followed by deficiencies in the IgG subclass (42%), IgM (40%), IgG (32%), and IgA (20%) [2]. Here, CD40LG is linked to Down syndrome.