Patient A displayed a poor Streptococcus pneumonia anti-capsular IgG response despite the fact that repeated culture proven pneumococcal infections led to high titers of IgM antibodies against these antigens (Fig 1A), resulting in a ratio of IgG- to IgM-Pn23-antibody serum titer of 0.03, well below the values observed in healthy adults either before or after Pn23 vaccination (ratio of IgG- to IgM-Pn23-antibody serum titer in 41 healthy adults [median, q5-q95]: before Pn23 vaccination, 2.00, 0.35–22.77; six-eight weeks after Pn23 vaccination ̧ 0.95, 0.17–45.89). The gene discussed is CD40LG; the disease is pneumococcal infection.