This variant of the hyper IgM syndrome is caused by mutation of the CD40LG gene. The genetic locus for this gene is Xq26. This gene codes for the CD40 ligand, which is expressed on T cells. When the CD40 ligand binds CD40 on B cells, then the B cell switches from producing IgM to producing IgA or IgG. In these patients a biopsy of a lymph node may show poor development of structural and germinal centers because of the lack of activation of B cells by the T cells in them.
Hyper-IgM syndrome type 1
Hyper-IgM syndrome type 5
Hyper-IgM syndrome type 2
Hyper-IgM syndrome type 3
Hyper-IgM syndrome type 4
Hyper IgM syndrome
Anti-IgLON5 disease
Wiskott–Aldrich syndrome