One brother is heterozygous (II.3) and the other (II.4) is homozygous for the TNFRSF13B/TACI C104R mutation.12 Given his asymptomatic status, the proband’s brother with the TACI C104R homozygous mutation (II.4) does not meet the Ameratunga et al.17 criteria for probable CVID; he has normal, albeit transient vaccine challenge responses despite being profoundly hypogammaglobulinemic (IgG 1.6 g l−1, NR 7–14; Table 1).12, 18 He has declined immunoglobulin replacement and remains in excellent health. Here, TNFRSF13B is linked to common variable immunodeficiency.