Hyper Immunoglobulin M syndromes (HIGM) are a heterogenous group of primary immunodeficiency disorder characterized by production of normal or increased levels of serum immunoglobulin M (IgM) and insufficient quantities of immunoglobulin G (IgG), immunoglobulin A (IgA) and immunoglobulin E (IgE). Here, CD40LG is linked to hyper-IgM syndrome.