Lymphopenia (70/μL; RV: 1400-4200*).Low CD4+ lymphocytes (13%; RV: 28.4-44.4***).Low serum IgG (252 mg/dL; RV: 639-1349**) IgA (37 mg/dL; RV: 70-312**) and IgM (24 mg/dL; RV: 56-352**).Reduced proliferation assays.Recurrent severe viral infections. The gene discussed is CD40LG; the disease is lymphopenia.