Laboratory tests revealed hypogammaglobulinemia [extremely low IgG (1.88–2.75 g/L; normal range, 8.27–14.17g/L), IgM (0.114–0.159 g/L; normal range, 1.22–2.56g/L), and IgA (<0.067 g/L; normal range, 0.86–1.92g/L) levels], which did not return to normal after intravenous immune globulin. Here, CD40LG is linked to agammaglobulinemia.