They include X-linked agammaglobulinemia (very low levels of all immunoglobulins with a B-lymphocyte count <2%) and Union of Immunological Societies (IUIS)84 hyper-IgM (normal or greatly increased values of IgM with low levels of other immunoglobulins).89 This evidence concerns the gene CD40LG and X-linked agammaglobulinemia.