Immunoglobulin replacement therapy is indicated in all patients with a severe immunoglobulin-G deficiency (serum immunoglobulin-G < 4 g/L) and in those with a high IgM phenotype (19, 71); it should also be considered for patients with milder humoral immune defects, recurrent infections, or low specific antibody responses despite booster immunization (56). The gene discussed is CD40LG; the disease is infection.