Patients with the X-linked Hyper IgM Syndrome show deficiency of a protein CD40 ligand found on the surface of T-lymphocytes. This primary immunodeficiency disease is inherited as an X linked recessive trait, and usually establish in boys only.
As a consequence of the deficiency of this protein, T-lymphocytes are unable to instruct B lymphocytes to switch their gamaglobulins production from IgM to IgG and IgA. As a result, patients have decreased levels of IgG and IgA and normal or elevated levels of IgM. Since CD40 ligand is important to other functions of T-lymphocytes, they also have a defect in some of the protective functions of their T-lymphocytes.
Most patients with the X-linked Hyper IgM (X-HIgM) syndrome develop clinical symptoms during their first year or second year of life. Increased susceptibility to infection is the most common problem in Hyper IgM syndrome.
This unusually produced IgM antibodies behave abnormally by binding to their self antigens present on neutrophils, platelets and other elements of the blood and tissue.
In addition to immune deficiency problems contact of IgM antibodies to their self antigens results in auto immune diseases.