The serum immunoglobulin levels were low (IgG, 34 mg/dL; IgA, 10 mg/dL; IgM, 46 mg/dL); the titers of specific antibodies against measles, rubella, pertussis, and varicella were extremely low after vaccination (Supplementary Table 1). The gene discussed is CD40LG; the disease is chickenpox.