The hyperimmunoglobulin M syndrome (HIGM) is a heterogeneous group of primary immunodeficiency disease (PID) caused by the defects of immunoglobulin class switch recombination which lead to the deficiency of IgG, IgA, and IgE with preserved or elevated levels of IgM [1]. The gene discussed is CD40LG; the disease is hyper-IgM syndrome type 1.